Climate change is an incessant global phenomenon and has turned contentious in the present century. Malaysia, a developing Asian country, has also undergone significant vicissitudes in climate, which has been projected with significant deviations in forthcoming decades. As per the available studies, climate changes may impact on the fertility, either via direct effects on the gonadal functions and neuroendocrine regulations or via several indirect effects on health, socioeconomic status, demeaning the quality of food and water. Malaysia is already observing a declining trend in the Total fertility rate (TFR) over the past few decades and is currently recorded below the replacement level of 2.1 which is insufficient to replace the present population. Moreover, climate changes reportedly play a role in the emergence and cessation of various infectious diseases. Besides its immediate effects, the long-term effects on health and fertility await to be unveiled. Despite the huge magnitude of the repercussion of climate changes in Malaysia, research that can explain the exact cause of the present reduction in fertility parameters in Malaysia or any measures to preserve the national population is surprisingly very scarce. Thus, the present review aims to elucidate the possible missing links by which climate changes are impairing fertility status in Malaysia.
Global climate change is the biggest threat to biodiversity and is severely affecting natural population of species via various mechanisms , . It has both direct and indirect impacts on human health as all the physiological adaptation strategies are failing in the face of shifting environmental phenomena , . Climate change may directly affect health by disrupting physiological functions or indirectly by impairing the overall environmental and sociodemographic factors indispensable for health, such as degradation of air and water quality, causing insecurity of food and shelter etc. . The major climate change is attained by global warming that induce high risk of disease outbreaks, sensitive to changes in weather, for example, cholera, malaria, malnutrition and natural disasters combined , , . Malaysia is also experiencing distubances of annual rainfall and gradual increase in surface warming, mainly since the past two decades . Moreover, Malaysia is also suffering from increasing trends of altered sea level, surface temperatures, and extreme weather events , . Therefore, changes in climate and their consequences should be paid research attentions.
The long-term effects of climate change on health and fertility of a population often get ignored while several factors independently or in combinations, are silently declining the overall fertility rate in Malaysia. Malaysia has observed a declining trend in the Total fertility rate (TFR) over the last three decades. In women, within the age range of 15–49 years, TFR is showing a decline from 4.9 babies per woman in 1970 to 1.8 babies in 2018 .
Considering high importance of reproductive health in persistence of a nation’s population, it is crucial in the present scenario to apprehend how climate change is affecting fertility parameters. This article is the first ever published review to present the possible impacts of climate changes in Malaysia over the fertility parameters. The article has individually addressed the most essential factors associated with climate change and carved out the possible pathways by which they may affect male and female reproduction. It provides a predictive outlook of the extent to which climate changes can modulate fertility status in Malaysia and aid preventive measures to be taken with adequate perception of the magnitude of this scenario.
Fertility status of Malaysia: current scenario
Malaysia is suffering from a gradual decline in fertility rate most prominently over the past 30 years. This is evidenced from the report depicting a reduction in TFR in Malaysia from 4.9 babies in 1970 to 1.8 babies in 2018 (per woman within the reproductive age) . In fact, since 2013, the recorded national TFR is below the replacement level of 2.1 which is definitely alarming. This suggests that the average number of babies born per woman in the country do not suffice the number required to replace herself and her partner in the population . The number of live births was 501,945 in 2018, a decrease of 1.3 percent as compared to 508,685 in 2017. The crude birth rate (CBR) declined from 15.9 (2017) to 15.5 (2018) per 1,000 population . To regulate the long-term effects of climate change on a population, the nation urgently needs strong predictive models that can effectively unveil the current impacts on the fertility status in both men and women as well as project future scenario of climate-change-mediated fertility modulations.
Malaysian government demographic reports of 2016 show the distribution of Malaysian population in the country with 80% living in Peninsular Malaysia, 11% in Sabah, while only 9% in Sarawak. Distribution of population according to ethnicity shows that population in Peninsular Malaysia bears about 61.8% Malays, 21.4% Chinese and 6.4% Indians and others make up the rest 0.9% .
Even before the implementation of the National Family Planning Program in 1966, fertility transformation in Peninsular Malaysia had already started. In 1960, Indians had 7.3 babies per woman, the highest TFR, followed by Chinese (6.3) and Malay (5.8) . However, the trend of TFR among the ethnic groups in Malaysia changed over time with Malays having highest fertility rate followed by the Chinese and then Indians since 1965. In Malaysia, the TFR declined from 5.7, in 1965, to 3.6, between 1966 and 1985, the TFR in Peninsular Malaysia declined from 5.7, in 1965, to 3.6, in 1985, and this was associated with high increase in use of contraceptive or the contraceptive prevalence rate (CPR) from 8 to 50%. CPR determines the proportion of married women using some form of contraception. CPR is defined as ‘the percentage of currently married women using any contraceptive method’ . The prevalence of contraception stagnated over the next two decades and even decreased, but the overall fertility rate decreased significantly through 3.0 in 2000, 2.5 in 2005 and further decreased to 2.3 in 2008.
The predicted TFR in Peninsular Malaysia, which is adequate to replace the current population, would be 3.8, based on the regression equation (TFR=7.27–0.07 CPR) from a study by Tsui (2001). The observed TFR of 1.8 in 2018 is below the expected value by 2.0, given a moderate CPR of about 50% . Such statistics pose a threat as Malaysia becomes an ageing nation with increased elderly population by 2030, with circumstances the increasing costs of health care and reduced youth force. As for the discrepancies in the association of TFR with CPR, it is reported for various other countries as well , . However, the lower than anticipated TFR has led to speculation that abortion and sterility are on the rise, along with increasing concern in understanding the reasons for this phenomenon.
Based on the statistics given by the Department of Statistics, Malaysia, in 1957, Chinese population contributed to 37.4% of the whole Malaysian population with TFR of 7.4 which declined to about 1.1 in 2018. The Malay and Indian population in Malaysia are facing similar drop in their TFR from 6.1 in 1957 to 2.4 in 2018 for Malay, and 8.0 in 1957 to 1.25 in 2018 for Indians. The overall TFR of Malaysian population declined from 2.1 in 2014, to 2.0 in 2015 and 1.8 in 2018 in women aged between 15 and 49 (Figure 1) , . Previous couple of studies in Malaysia had put forth links among the socioeconomic factors, ethnicity and fertility rate , . While intermediate variables are important to explain differences and reduction in fertility status in Malaysia, there is a serious lack of research on the subject.
How climate change may impact fertility?
To date, multiple studies have reported that ‘climate change is the greatest threat to global health in the 21st century’ , . Climate change poses an urgent and significant risk to human health and human survival worldwide. Everyone is at danger, whether affected via heatwaves, severe weather events, drought, starvation, altered illnesses and water pollution leading to diarrhoea, hunger, mass migration or any subsequent issues . Developing countries are likely to be most heavily affected by climate change, with women bearing the greatest toll.
In Malaysia, very little work has been done on projecting potential impacts of climate change on health burdens. Climate change affects human health through a range of direct or indirect exposures. In tandem with obvious and visible extreme events of floods, forest fires and heat waves, there exist certain silent factors like global warming having chronic effects on health and fertility . The reproductive tissues function only within a range of temperature. Thus, when the ambient temperature exceeds that critical temperature, it adversely affects reproductive functions via common mechanisms of gonadal heat shock, oxidative stress (OS) and alterations in endocrine milieu. Heat stress can be an environmental as well as an occupational hazard that can lead to chronic illnesses and even death, from the after effects of heat stroke , . Besides temperature changes, accumulation of toxic contaminants in air also contribute to various reproductive disorders and can also induce OS. These environmental cues can induce unregulated production of free radicals, reactive oxygen species (ROS) and reactive nitrogen species (RNS). The chain of oxidative damage severely affects gonadal functions such as impairment of gametogenesis, gamete chromatin integrity, mitochondrial functions as well as increased germ cell apoptosis. This leads to decreased semen quality in men and reduced oocyte quality and uterine receptivity in females. The disruption in the hypothalamic–pituitary–gonadal (HPG) axis alter the release of gonadotropin releasing hormone (GnRH) and subsequent tropic hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH), thereby leading to decreased testosterone levels in males, oestrogenic and progesterone in females, impairing gonadal functions (Figure 2). Natural calamities like storms, floods, draught and changes in rainfall pattern can affect socioeconomic status of a nation inflicting malnutrition, poor sanitation, increased food and water-borne diseases, emergence and spread of infectious diseases affecting overall health and thereby indirectly posing threat to fertility.
Climate change in Malaysia and its impacts on fertility
Temperature change and reproductive health
Climate change adversely affects global thermal environment and will continue to increase local temperature as well as frequency of heat waves . The set-point temperature in humans is 37 °C and potentially lethal effects associated with hyperthermia are usual at body temperatures above 40–41 °C . Regulation of core body temperature is, therefore, not surprisingly a priority over several other physiological functions.
In Malaysia, the approximate rate of increase in mean temperature has been reported to be 0.25 °C per decade in the peninsular Malaysia, 0.20 °C per decade in Sabah and 0.14 °C per decade in Sarawak . The high spikes in ambient temperature in 1972, 1972, 1991, 1997–1998 and 2015–2016 were suggested owing to El Nino which was probably the strongest in the 2015–2016 . Intergovernmental Panel on Climate Change (IPCC) had reported that global mean surface temperature has increased 0.74 °C between 1905 and 2005 and predicts an increase of 2–4.5 °C over the next 100 years. In Malaysia, surface temperature of last four decades has increased between 2.7 and 4.0 °C per century . Tang (2019) has reported that the yearly moving average of mean daily temperature shows an uptrend in different parts of Malaysia, including, Kota Kinabalu, Kuching, Malacca, Kuantan and Subang Jaya. Increase in the annual moving average of mean daily temperature, was shown to be lowest in magnitude for Kuching, followed by slightly higher in Kota Kinabalu, Malacca, Kuantan and Subang Jaya . The information here is in line with the reports put forth by the Malaysian Meteorological Department (2009) which also depicted that Kuching has the least rise in temperature owing to its slower development pace .
There is available literature that emphasizes the impact of environmental temperature on the viability of a population. The lethal limit of temperature is termed as the “critical thermal limit” (CTL). But a sublethal level of ambient temperature can impair the reproductive functions rendering a population with compromised fecundity .
Temperature change and male reproductive functions
Reproductive functions in both the genders are immensely affected by temperature changes . Data on the alterations in Malaysian men reproductive functions due to temperature changes are not available. However, studies on animal shows that high ambient temperature impairs spermatogenesis, effects the quality of sperm, leads to abnormal sperm morphology and reduces sperm motility , . In most of the animals including human, testes are suspended outside the body cavity in a scrotum such that the intratesticular temperature is much lower than the core body temperature. In the testis, there is a complex thermoregulatory mechanism that is mediated by counter-current heat exchange between blood with higher temperature that enters testes and the ones with lower temperature exiting testes via the pampiniform plexus . Therefore, the scrotum is so built because of the need for low temperatures for either spermatogenesis, sperm storage or for reducing mutations in gamete DNA . An increase in testicular temperature in mammals with external testes result in decreased sperm production, decreased sperm motility and increased morphologically abnormal sperm in the ejaculate . Two muscles further monitor this degree of cooling: the scrotum’s tunica dartos that regulate the area of the scrotum and the muscle of the cremaster that regulates the location of the scrotum compared with the body. The testicular cells that are reportedly most vulnerable to get damaged by increase in ambient temperature are primary spermatocytes and early spermatids, but effects on spermatogonia and Sertoli cells have also been observed . Among the major causes of thermal damage to sperm, oxidative stress (OS) plays a pivotal role inducing lipid peroxidation of sperm membrane, apoptosis of germ cells, disruption of mitochondrial functions as well as sperm chromatin disintegration by DNA fragmentation , , , , , , .
The developmental competency of the resulting embryo can also be impaired if the fertilization is attained via spermatozoon affected by heat stress . These include epigenetic alterations in embryonic development. A recent study reported the effects of increased environmental temperature on sperm quality and embryo development in Holstein bulls. It has showed reduced rates of blastocyst formation on insemination sperm exposed to high temperature .
In another context, it is significant to put forth that Malaysia is a highly epidemic region for dengue, malaria, chikungunya and other vector borne diseases , , . It is reported that prevalence of these diseases increases with increased ambient temperature . Thus, an indirect prediction can be made on these infection-induced alterations in semen quality and male fertility status. Reports have shown the effects of various microorganisms on semen quality deterioration and altered male fertility , , , , . Though, studies reporting direct relations of these infection-induced male sub- or infertility in Malaysian peninsula are scanty, this could be presumed that these may impact significantly in reproductive health of Malaysian men.
Temperature change in female reproduction and pregnancy outcomes
As discussed earlier, overall TFR of Malaysia is declining in a significant rate and is below the replacement level of 2.1 (1.8 in 2018) implying that offspring produced by each women in reproductive age do not suffice the number required to replace herself and her male counterpart in the Malaysian population . Both male and female factors contribute to this decline in fertility rate. Amongst various factors affecting fertility parameters, ambient temperature changes do play critical role . The ovarian follicle pool and the enclosed oocytes are very susceptible to hyperthermia among the components of the female reproductive tract. Heat-induced changes within small antral follicles can later be expressed as impaired maturation and developmental capabilities of the ovulating oocyte . The recent climate changes and exposure to elevated ambient temperatures are curbing normal oogenesis, menstrual cycle, impregnation rates, pregnancy outcomes as well as offspring development , , . Heat stress can disrupt the production and function of the oocyte for female gametes. The ability of oocyte to get fertilized and grow in lactating cows has been shown to deteriorate during the periods of the year in conjunct with heat stress . There is plenty of evidence that heat stress can affect the oocyte and follicle encasing it .
Extreme ambient temperatures also affect embryonic development. Study on cow model shows that hyperthermia at day-1 of pregnancy impairs early embryonic development. In mice, high ambient temperatures for one day following mating disrupted normal embryonic development . Elevated temperatures during mid-gestation also reduced foetal weights . An animal study conducted by Hamid et al. (2012) in Universiti Putra Malaysia has reported the effects of elevated ambient temperature on reproductive outcomes during different stages of pregnancy and the prenatal heat stress on offspring growth. They have reported from that exposure to elevated ambient temperature during pre- and peri-implantation has stronger adverse effects on reproductive outcomes and offspring growth than post-implantation exposure .
Temperature and reproductive hormones
Reproductive hormones and their crosstalk with other hormones intricately regulate the male and female reproductive functions. Few studies are available, although none from Malaysia, on the effects of elevated environmental temperature on the secretion of reproductive hormones. Initially studies performed in bulls and boars have put forth that heat stress leads to an initial reduction in the levels of testosterone concentrations , . Recent studies have shown that extreme heat can lead to compromised levels of luteinizing hormone, follicle-stimulating hormone besides diminished levels of testosterone. These in turn cause damage to the spermatogenic cell lineage, reduced semen quality and sperm DNA fragmentation in males , . In females, the reproductive hormones are associated intricately with endogenous temperature regulation of the autonomic nervous system, such that, oestradiol and progesterone have both central and peripheral influence on thermoregulation, where oestradiol is used to facilitate heat dissipation and progesterone mediates heat storage and increased body temperatures . High ambient temperature affects the secretion of both gonadotropins (LH and FSH) and gonadotrophin-releasing hormone (GnRH) which disrupt development and maturation of oocyte, early embryonic development, fetal and placental growth as well as lactation. Such deleterious effects of heat stress are either the result of heat stress hyperthermia or the physiological changes made to regulate body temperature by heat-stressed animals .
Thus, we need effective research on the effects of ambient temperature changes on Malaysian population with particular emphasis to exposure-time adversely affecting male and female fertility.
Haze, air pollution and its impact on fertility
Episodes of haze in Southeast Asia in 1983, 1984, 1991, 1994 and 1997 caught the attention of the environmental management of Malaysia and began to enhance awareness of air pollution owing to climate change . This followed the establishment of Malaysian Air Quality Guidelines, the Air Pollution Index, and the Haze Action Plan to improve air quality . The predominant air pollutants in Malaysia include carbon monoxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3) and Suspended Particulate Matter (SPM). Several big cities in Malaysia also possess high levels of CO, O x , SO2 and Pb . A very concerning factor for diminished air quality in Malaysia is the frequent high amounts of smoke and haze that drift into Malaysia for the past 40 years, caused by the uncontrolled fires across Indonesia. The haze negatively correlates with human health, climate and economy . Reports from a wildlife rescue centre in Borneo on orangutans depicted that haze results in respiratory tract infection, dehydration, malnourishment and it is predicted that the long-term effects can lead to birth defects and reproductive failure. A recent study by Tajudin et al. (2019) on the health effects of air pollution of Kuala Lumpur city has reported that exposure to air pollutants and trace gases can lead to both immediate and delayed effects on cardiovascular, respiratory and other health issues. Not adequate number of studies are available that depicted the impact of air pollution upon health of Malaysian population, thereby making it arduous to postulate the impact of air pollution over reproductive health in Malaysia . However, there are few studies that can be mentioned, such as the one analysing the health impact of the forest fire of 1997. Another study had showed that at the peak time of smoke haze, there is many fold increase in outpatients mainly suffering from respiratory diseases, in the hospitals of Sarawak, Kuching as well as in the Kuala Lumpur General Hospital . There is also evidence of air-pollution madiated increased cases of acute respiratory infection, conjuctivitis and asthma, in hospitals in Kuala Lumpur, between August–September, 1997 .
It is high time to generate extensive evidences on the actual impacts of haze of reproductive health of Malaysian population that is crucial for population persistence.
Female reproductive system has a unique way to respond to toxic exposure, particularly towards the pollutants with oestrogenic potential  such as, polycyclic aromatic hydrocarbons, which mimic natural hormone activities and varying regulation and function of the endocrine system . Impacts of air pollutants on reproductive health often result from short-term exposure during the vulnerable phases of ovulation or foetal organogenesis. Effects of certain toxicants can remain hidden for years due to accumulation in parental tissues and later may be during pregnancy, lactation or even post-natal development . It is shown that particulate matter of size less than 10 μm can affect pregnant women mainly at the first trimester of pregnancy and affect pregnancy duration, impaired foetal growth as well as negative or undesired pregnancy outcome . The knowledge about mechanisms of these phenomena is limited. Menstrual disturbances, most prominently luteal phase shortening, have been documented as a common health hazard from fossil fuel combustion .
In terms of sperm production, motility and/or morphology, numerous animal- and human-based research on exposure to environmental toxins indicate a negative impact on the semen quality , , . Such toxins can have oestrogenic and/or anti-androgenic effects, which in turn modify the hypothalamic–pituitary–gonadal (HPG) axis, trigger damage to sperm DNA or cause epigenetic changes in sperms , , .
Heavy rainfall, flood and its impact on fertility
Heavy rain and runoff may contribute to surface water pollution and may again endanger the supply of clean water. After floods, the risk of disease outbreaks such as hepatitis-E, gastrointestinal disease and leptospirosis was found to increase, particularly in areas with poor hygiene and displaced populations . Malaysia has witnessed several major floods in the last two decades , , , , ,  (Table 1).
|Occurrence||Description and consequences|
|26 December 2001||Tropical Storm Vamei was a tropical Pacific cyclone developed closer to the equator than any other tropical cyclone. Vamei (also known as the Typhoon Vamei) originated in the South China Sea at 1.4°N on 26 December as the last storm in 2001 during the Pacific typhoon season. This was called as a typhoon as it had sustained wind speed of 120 km/h (75 mph) and appeared like an eye. It caused landslides and severe flooding in eastern Peninsular Malaysia, with five deaths and a huge economic damage of $3.6 million (2001).|
|December 2006–January 2007||Typhoon Utor passed across the central Philippines in December 2006, while its residual moisture indirectly led to immense flooding in Malaysia. This series of floods affected the region for a long duration till it ceased in February 2007 . The tropical moisture together with high velocity monsoon winds continued to persistent precipitation over Malaysia, especially the states of Johor, Pahang and Malacca. Peak rainfall of 567.8 mm (22.35 in) was recorded in Bandar Muadzam Shah with almost similar records in surrounding region, over a four-day period of the rainfall spree . Segamat and Kota Tinggi were adversely affected by the floods and turned inaccessible by land. There were eight deaths recorded from this historical flooding.|
|October–November 2010||A devastating flood series was observed in Thailand and Malaysia in 2010, due to abnormal late arrival of monsoon moisture over the Bay of Bengal. This development led to overflow of Chao Phraya, the meeting zone of rivers and affected Bangkok, and subsequently after two weeks, it induced a tropical depression in the further south causing floods in Malaysian states of Kedah and Perlis. These flash floods severely affected health, food supply, education sectors, transportation and overall economy in Malaysia. This contaminated water supply in Kedah and Perlis, which compelled these states to thrive on water supplies from the neighbouring Perak state. As per the reports from the federal government, the floods damaged over 45,000 ha of rice fields in Kedah alone, for which the government pledged a compensation of 26 million ringgit to the farmers . Almost 50,000 people were evacuated, and four deaths were recorded as the consequence of this flood series .|
|January–February 2014||Various regions of Sabah including Menggatal, Penampang and Tuaran were flooded due to heavy rainfall and flash flooding. As of 15 February 2014, more than 4,000 people had been evacuated to 22 relief centres in Beaufort and Tenom. There were two reported deaths and property damage scored to millions of ringgits .|
|October–November 2014||The Peninsular Malaysia tornado outbreak of 2014 is a natural phenomenon that took place in the state of Kedah and Selangor, Malaysia from 14 October to 12 November 2014. Kedah and Selangor were hit by episodes of EF3 tornado, each lasting for 10–15 min with wind speed up to 240 km/h. The frequent tornado formation was speculated to have been due to changes in monsoon. This calamity rendered 6,000 homeless (1,883 homes destroyed) and economic damage of about $1.5 billion (USD) (as per the currency rate of the time in 2014).|
|December 2014–January 2015||The series of floods in affected most of the Southeast Asian countries and reportedly caused by the northeast monsoon, affecting more than 417,000 people and at least 21 reported deaths. Malaysian East Coast were severely affected by the flooding, the regions included Pahang, Terengganu and Kelantan states. Moreover, states in Peninsular Malaysia including Johor, Perak, Selangor and Perlis and a state in East Malaysia, Sabah also experienced the floods due to the heavy rainfalls with peak of 255 mm. These floods have been described as the most severe floods in past few decades .|
|January–February 2015||Heavy intensity rainfall from 17 January 2015 till the end of February, led to flooding across the Eastern Malaysia, mainly in Sarawak and Sabah. The number of evacuated people were estimated to be around 13,878 people, with property damage of almost $1.03 billion (USD) and one casualty of a teenage girl was reported, a teenage girl .|
|February–March 2016||Heavy rainfall occurring in the first half of February 2016, led to immense flood in Malaysian states including Bau, Samarahan and Serian in Sarawak, Tangkak, Ledang and Segamat in Johor and Alor Gajah, Central Malacca and Jasin in Malacca and parts of Negeri Sembilan. Three casualties were reported, and property damage were estimated to be $550 million (USD) .|
|December 2016–early 2017||Flooding that occurred in southern Thailand had significant effects on Malaysian states of Kelantan and Terengganu. Changes in the annual monsoon season was the major cause of this flood and led to an estimated loss of USD 4 billion, contributing to severe damage in agriculture, infrastructure and tourism .|
|October 2017||Typhoon Paolo, originated from a tropical cyclone, stroked across Sabah. It was characterised by strong wind and heavy rain. It had dreadful consequence rendering 100 deaths, more than 200 missing cases and about 4,000 people became homeless .|
|November 2017||A sudden flood in Penang lead to evacuation of approximately 3000 people. The calamity was accompanied by strong winds and long duration torrential rain and was reportedly developed from tropical cyclone. This calamity resulted in at least 7 deaths and over 10,000 after floods swept through the northern states of Penang and Kedah in peninsular Malaysia .|
|December 2017||Strong wind blew across the west coast of Sarawak, Sabah and Labuan at 40–50 km/h and was caused by Tropical Storm Kai-Tak that originated in the Western Pacific Ocean .|
|Jan 2018||The annual northeast monsoon caused high intensity rainfall that led to floods in Malaysia particularly in the states of Terengganu, Johor, Pahang and Sabah. The flood killed two in Pahang and caused about 12,000 people to be displaced nationwide. Kuantan and Rompin districts in Pahang were the most affected regions. Malaysia’s National Disaster Management Agency (NDMA) reported that 9 relief centres were set in two districts, which sheltered more than 2,725 displaced people .|
There is no direct Malaysian report elucidating the impact of flood and water quality on male and female reproductive health. However, flood causes decreased water quality , which affects reproductive health in both . Floods can affect the health of new-borns by affecting the pregnanat women in terms of both mental and physical health and diminishing their capability to avail health services. Studies of women with prenatal disaster exposure have revealed that high levels of prenatal stress positively correlate with poor pregnancy outcomes  and poor health outcomes in offspring, that include their behavioural and psychiatric features . The risk of adverse effects on birth outcomes and child’s health increase with magnitude and duration of disaster exposure within the gestational period . Floods and changes in rainfall pattern severely creek into socioeconomic status of the population inflicting malnutrition, poor sanitation, food- and water-borne infectious diseases, which individually or as combined factors exert their toll on fertility.
Climate change, infectious diseases and infertility
Increasing global temperatures will shorten the length of winter, facilitating potential disease-carrying agents and aid further spread of diseases . Climate change may render the habitats unsuited for animals, compelling them to migrate more to urban areas and thus enhancing the risk of transmission of zoonotic diseases . The World Health Organization (WHO) warned in 2007 that emerging infectious diseases are becoming a growing threat in the face of increasing urbanization, resistance to antimicrobials and climate change .
Dengue is a prevalent disease in Malaysia. It was projected that climate changes have great influence over the dengue prevalence in Malaysia . The influence of climate change on monsoon seasons bring about variation in transmission of dengue in Malaysia , . Institute for Medical Research (IMR) model depicted that high rainfall leads to higher dengue transmission. The vector-borne diseases, mainly dengue and malaria also increase with temperature fluctuations due to increased availability of the vector breeding habitats. For example, between January 1 and August 20, 2016, a total of 71,590 dengue cases were reported in Malaysia with 162 deaths. The bulk of the cases were in the states of Selangor, Kelantan, Johor and Kuala Lumpur. Climate change would have a direct effect on vector distribution and consequently in diseases, such as, dengue, malaria, filariasis and Japanese encephalitis (JE) as well , . Food and water-borne diseases also are predominant in tropical and subtropical countries which may be the indirect health impacts of climate change. These include: (i) diarrhoeal diseases caused by a variety of organisms (such as, Escherichia coli, Vibrio cholera, salmonellae and viruses), (ii) other viral diseases (such as, hepatitis A and poliomyelitis) and (iii) protozoan diseases (such as giardiasis and amoebic dysentery) .
Dengue may significantly contribute in impairment of reproductive parameters , . A single centred study was conducted to analyse the patterns and outcomes of dengue infection amongst pregnant women in Malaysia. It suggested that dengue infection during pregnancy may result in maternal morbidity and death, particularly in premature baby delivery. In the case of febrile pregnant women, dengue infection should be strongly suspected .
The recently emerged novel coronavirus, SARS-CoV-2 causing the disease COVID-19, has raised waves of fear across the globe and Malaysia is one of the countries moderately affected by the same. A correlation between metrological parameters and COVID-19 cases has already been reported . As reported till 23 July 2020, a total of 15.1 million people around the world have been infected with COVID-19 since the coronavirus outbreak began over a couple of months ago. The Ministry of Health (MoH) of Malaysia has confirmed that COVID-19 cases in Malaysia have increased to 8,831 (as per reports on 23 July 2020) . This is not the first time in recent history that the world has struggled with a global epidemic—there was the severe acute respiratory syndrome (SARS) in 2003, the Middle East coronavirus respiratory syndrome (MERS) first identified in 2012 and the Zika virus in 2015–2016—and this coronavirus is unlikely to be the last . However, unlike coronavirus infections in pregnant women caused by SARS and MERS, COVID-19 have not yet posed threat to maternal survival. At this point in the global pandemic of COVID-19 infection, there is no evidence that SARS-CoV-2 undergoes intrauterine or transplacental transmission from infected pregnant women to their foetus. A very recent study has suggested that the SARS-CoV-2 might directly bind to receptors in the reproductive tissues of patients  and may impair gonadal functions. The study encourages long-term interventions and follow up over the COVID-19 affected men, to unveil the exact effects of this virus on male fertility , , , , .
Climate changes, socioeconomic and demographic factors and infertility
Malaysia is a fast-growing developing country. So, there are scopes of regular shifts in economic variables that would impact food security. There is a wide range of economic channels through which climate change can affect fertility rate of a nation, that includes sectoral reallocation, wage inequalities among gender, longevity and child mortality . Through its economic effects, climate change could have a substantial impact on population growth, primarily by influencing behaviour of people towards increasing family size. It influences their decision on whether to devote more time and money for child-rearing, or channelize those to have more children . The cross-relations among climate change-sociodemographic factors-infertility are subject for detailed interventions at different strata in Malaysian population which is presently lacking. However, a recent study on 300 men attending the Fertility Clinic, International Islamic University Malaysia (IIUM), demonstrated significant associations between critical sociodemographic factors, such as household income, educational attainment and others, with levels of seminal abnormalities in the subjects .
The climate conditions in Malaysia are evolving very rapidly and have had adverse effects on food production . Even that, food insecurity in households is not only related to social and economic factors, but also linked significantly to the direct and indirect effects of climate factors . Previous studies have shown that 50% or more of the rural low-income households face certain food insecurity. A recent study showed that 23.3% of poor and low-income households are poorly food-insecure, 14.3% are moderately food-insecure and 9.6% are seriously food-insecure in Malaysia . The global food supply system faces serious new threats from economic and related crises and climate change, which have a direct effect on poor people’s nutritional well-being by reducing their access to nutritious food. In deal with this, vulnerable populations prefer calorie-rich, but nutrient-poor, food consumption. The consequence is a decrease in dietary quality and ultimately in quantity, rising micronutrient malnutrition (or secret hunger) and exacerbating pre-existing inequalities that contribute to poorer health, lower incomes and decreased physical and intellectual ability . Inadequate nutritional intake is undeniably associated with poor reproductive health in both men and women. In men, it correlates with increased testicular and seminal oxidative stress and associated sperm DNA fragmentation and impaired chromatin condensation. Epigenetic modulation has been reported, with transmission to the offspring . However, direct causality has not been demonstrated.
Inadequate nutrition is closely linked to female reproductive pathophysiology . Deficient food intake, insufficient nutritional diets, extreme dietary restrictions and general lack of nutrients result in loss of both body weight and physical performance, delayed puberty, postpartum time lengthening to pregnancy, lower levels of gonadotropin secretion with hormonal cyclicity changes and increased infertility. Poor intakes of proteins, micro- and macro-minerals and vitamins are associated with reduced reproductive efficiency, as the altered energy balance is directly correlated with reduced ovulatory maturation in women. It was reported that maternal malnutrition adversely affects foetal health, resulting in poor development and altered body composition with low muscle mass, poor brain development and metabolism , , modulations at the hormonal crosstalk, receptor expressions as well as genetic and epigenetic constitutions , . In the long term, these alterations will result in low cognitive development, incompetency in education, low immunity, inadequate working potential and an increased risk of several chronic diseases . It was also proposed that there exist “proximal levers” to facilitate positive attitudes and measures to ensure optimal foetal, infant and childhood nutrition .
Future perspectives and conclusion
The projections of climate change in Malaysia over the next few decades are worrying enough with speculation of extreme variations in rainfall, increase in ambient temperature and lack of clean water (Table 2: , , , , ). These, even at less than extreme levels may affect the fertility parameters of Malaysian population which is already following a declining trend and the climate change may be an essential role player in the process, either directly or indirectly. The direct impact of climate change on reproductive functions may involve heat-induced physiological alterations that impair the structure and functions at the tissue or cellular levels or disrupt the orchestration of hormones regulating the reproductive functions. There are number of indirect means by which climate change can affect fertility. Flood, drought or even fluctuations in ambient temperature may facilitate emergence of novel infectious micro-organisms that can cause and spread both systemic and reproductive infections leading to subfertility or infertility. In addition, climate changes, national socio-economic status and food supply are closely linked, and sociodemographic or economic alterations are in turn important determinants of fertility rate in a population. Moreover, deterioration in quality or quantity of food in any region, may severely affect overall health as well as fecundity of the population. Since, Malaysia lacks proper research to support the possible effects of climate change on fertility, the present report provides a probable scenario based on worldwide evidence of the mechanism by which Malaysian fertility is and will fall victim of the ongoing climate changes, and thereby, further studies should be encouraged in this direction.
|Malaysian Meteorological Department (2009) ||The estimated rise in temperature till 2019 is between 1.0 and 3.5 °C for East Malaysia and between 1.1 °C and 3.6 °C for the Peninsular Malaysia. Owing to its highly variable precipitation-modulating factor, no certain precipitation pattern was reported. During the 21st century, the precipitation on the West Coast increased and precipitation on the East Coast of the Peninsular Malaysia decreased. Until the end of 21st century, major rises in precipitation were expected over west Sarawak.|
|Kwan et al. ||Between 2070 and 2099, increased probability of intense rains on the west coast of Malaysia was expected in September to November. In some areas of Malaysian Borneo, early monsoon rainfall was predicted. Higher frequency of extreme warm temperatures and small decreases in cold extremes were forecast.|
|Loh et al. ||The rise in temperature between 2.5 and 3.9 °C, 2.7–4.2 °C and 1.7–3.1 °C was projected at the national level by the end of the 21st century in three different emission scenarios (A2, A1B and B2). For drier months from December to May, and rain months from June to November, a high rainfall variability was expected.|
|Syafrina et al. ||RCP 6.0 scenarios were used to predict increase in rainfall in hours and 24 h from the year 2081–2100, with a wider spatial distribution.|
|Amin et al. ||In November from 2030 to 2070, and also in November and December from 2070 to 2100, the simulation showed a substantial increase in mean monthly flows in the Dungun watershed. The rise in flow from April to May and July to October has been projected between 2040 and 2100 for Muda Watershed. (GCM for climate projection and watershed hydrology model (WEHY) for hydrologic simulations over Muda and Dungun watershed in the Peninsular Malaysia)|
Research funding: None declared.
Author contributions: R Jegasothy: Conceptualization, Manuscript editing and review. P Sengupta: Literature search, Manuscript writing, Manuscript editing and review. S Dutta: Literature search, Manuscript writing, Manuscript editing and review. R Jeganathan: Manuscript editing and review. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
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