As coronavirus disease 2019 (COVID-19) pandemic continues, an increasing number of countries and territories are adopting restrictive measures based on physical (“social”) distancing, aimed at preventing human-to-human transmission and thereby limiting virus propagation. Nationwide lockdowns, encompassing mass quarantine under stay-at-home ordinances, have already been proven effective to contain the COVID-19 outbreak in some countries. Nevertheless, a prolonged homestay may also be associated with potential side effects, which may jeopardize people’s health and thus must be recognized and mitigated in a way without violating local ordinances. Some of the most important undesirable consequences of prolonged homestay such as physical inactivity, weight gain, behavioral addiction disorders, insufficient sunlight exposure and social isolation will be critically addressed in this article, which also aims to provide some tentative recommendations for the alleviation of side effects.
Coronavirus disease 2019, abbreviated to COVID-19, is a viral infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) , . As with other members of the Coronaviridae family, inter-human transmission of this microorganism is mostly due to respiratory tract infection, mediated by the so-called respiratory droplets, which are formed by water and various inclusions, and can be generated while talking, breathing, coughing or sneezing . Human droplets are circular elements with ~5 μm diameter that rapidly fall to the ground under gravity after being produced, which usually limits the transmission distance at less than 1 m during normal breathing (Figure 1) . Some additional vehicles of potential contagion have been identified (e.g. direct contact with infected environmental or biological materials such as feces or saliva) , , , though respiratory droplets remain the largest source of contagion.
The most recent statistics of the World Health Organization (WHO) attests that SARS-CoV-2 has already infected nearly 635,000 persons around the world, causing over 30,000 deaths . These numbers are inevitably destined to grow as definitive vaccines and cures for COVID-19 are unlikely to be identified soon . As such, a combination of contact tracing and social isolation seems to be the most effective strategy to control the COVID-19 outbreak , as this strategy will be effective for flattening the curve of new infections due to human-to-human transmission, limiting morbidity, mortality and the ensuing surge of demand on healthcare system.
Lockdown, a term conventionally used as surrogate for “mass quarantine”, is typically based on “stay-at-home” or “shelter-in-place” ordinances given by a public (either national or regional) government or authority, for imposing social distancing and hence limiting or completely abolishing the movement of the population inside and outside a specific area. It is hence mostly used as for counteracting an ongoing outbreak, mandating residents to stay inside their homes, except for carrying out essential activities (health visits, tending to a vulnerable person, purchasing medicines, food and beverages) or providing essential work (e.g. healthcare and social care sectors, police and armed forces, firefighting, water and electricity supply, critical manufacturing). Other non-essential activities are hence stopped or carried out from home , .
At the time of writing this article (March 30, 2020), nationwide restrictions for limiting the spread of SARS-CoV-2 infections have been established by over 50 countries around the world, including the UK, Italy, Spain, France, Germany, Austria, South Africa, India, Colombia, New Zealand and several US states, with many others to follow as soon as the numbers of COVID-19 cases continue to rise exponentially. Currently, we can estimate that over 280 million people are under lockdown throughout Europe, 150 million in the US, nearly 1.3 billion in India and still 50–60 million in China. Overall, it can hence be estimated that over one-third of humanity is subjected to some form of restrictive measures . This strategy has been proven effective for containing the COVID-19 outbreak in China, also limiting the exportation of infected cases outside the country , . Nevertheless, stay-at-home orders may also be associated with numerous side effects, especially when the lockdown is protracted for months, thereby disrupting social habits and jeopardizing personal health. Strategies, which do not violate local ordinances, need to be urgently identified and established for preventing these derangements.
To that end, the most important undesirable effects of prolonged homestay such as physical inactivity, weight gain, behavioral addiction disorders, insufficient sunlight exposure and social isolation will be critically addressed in this article, which also aims to provide some tentative recommendations for the alleviation of side effects. These problems and our recommended remedies are summarized in Table 1.
|Risk factor||Most relevant health consequences||Remedies|
|Physical inactivity||– Osteoporosis
– Cardiovascular disease
|– Keep enough distance while exercising outside
– Practice indoor exercise
– Use video- or app-guided equipment-free training
– Use the stairs
– Avoid sports injuries
|Weight gain||– Diabetes
– Cardiovascular disease
– Pulmonary embolism
– Low back pain
|– Hypocaloric diets
– Reduced total fat content
– Prefer low-carbohydrate and high-protein foods
– Increase intake of dietary fiber
– Supplement diet with immunomodulatory foods
|Behavioral addiction||– Psychological disturbances
– Neurological complications
– Musculoskeletal disorders
|– Controlled and balanced usage of electronic devices
– Use of external stoppers
– Software programs controlling usage time
– Development of personal inventories
|Insufficient sunlight exposure||– Low vitamin D levels||– Vitamin D dietary supplementation
– Diet enriched in foods with high vitamin D
|Social isolation||– Depression
– Misidentification of health deterioration
|– Delivering groceries and essential medicines
– Reinforce social care measures
– More frequent contacts with smartphone or social media
The dramatic reduction of physical activity due to mandatory homestay is perhaps one of the most apparent consequences of complete lockdown, not only for active individuals habitually practicing recreational sports, but also for those who go to work by walking or cycling, or whose job includes physical activity of some sorts.
It has already been defined that the combination of abrupt interruption of physical exercise and prolonged inactivity may promote many adverse health changes, including development of insulin resistance, muscle atrophy and bone loss, decreased aerobic capacity, increased blood pressure and heart frequency, fatty liver disease and/or nonalcoholic steatohepatitis, dyslipidemia, as well as higher risk of collapsing upon resuming exercise . The important biological and metabolic adaptations would hence translate into a considerable higher risk of developing osteoporosis , diabetes , cardiovascular disease , cancer , dementia  as well as overweight/obesity , among others. Overall, the enhanced physical inactivity-attributable disease burden not only fosters a remarkably higher risk of disability, but is also associated with a nearly 24% increased risk of all-cause mortality among the general population .
The current WHO global recommendations on physical activity for health promotion and maintenance indicate that adults should engage in not less than 150 min per week of moderate-intensity aerobic physical activity, or not less than 75 min per week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity activity . This most frequently translates into the practice of recreational or leisure activities such as walking, cycling, swimming, gardening, hiking, dancing and household working. Additionally, the WHO recommends performing some muscle-strengthening activities, involving major muscle groups, for 2 or more days on a weekly basis.
Fulfillment of these recommendations is inherently challenging for citizens residing in lockdown areas, as movements outside one’s residence are almost totally banned. People not involved in essential services are forced to stay inside their houses for weeks (or even months), only allowed to move sporadically for health or alimentary purposes. Nevertheless, the shelter-in-place orders established by some countries, like Italy and Germany, for example , enable some outdoor physical activity, provided that a sufficient interpersonal distance can be guaranteed (i.e. >1 m, >1.5 m or >2 m depending on local ordinances), and that the exercise is completed in close proximity of one’s home residence. The maintenance of a sufficient interpersonal distance is crucial, almost unavoidable, as SARS-CoV-2 is mostly transmitted by droplets . The risk of infection may hence be enormously magnified in subjects practicing narrow sports activities, such as contact sports or side-by-side running or cycling, as a consequence of increased ventilatory demand, which is then accompanied by increase of respiratory frequency (i.e. from 15 to 20, up to 50 breaths per min) and enhanced volume of exhaled air , . An exception to total stay-at-home rule for performing some forms of outdoor exercise may contribute to counteract the detrimental changes resulting from prolonged physical inactivity. Engagement in some forms of indoor physical activity is another viable solution. Although fast (power) walking, running and cycling are unfeasible for the vast majority of subjects who are lacking indoor exercise equipment (e.g. treadmills, stationary bikes, etc.), strength or aerobic workout without the need of very specific and expensive equipment other than exercise bands, fitness ball or weights can still be performed, driven by video- or app-guided equipment-free training . Basic things that can be found at home may also help, such as the stairs for climbing, performing step exercise or even strength training.
Another important aspect is the absolute need to avoid any type of sports injury (direct, indirect or overuse) while practicing exercise . As most healthcare resources, especially emergency departments (EDs) and intensive care units (ICUs), are now overwhelmed managing the massive number of COVID-19 patients requiring urgent care , preventing any additional strain of care due to unwarranted injuries on an already exhausted system is vital.
The risk of weight gain, up to developing overweight or obesity, is one of the most significant implications of physical inactivity . Overweight and obesity, defined by the WHO as a body mass index (BMI) ≥25 and ≥30 kg/m2, respectively , are accompanied by a kaleidoscope of metabolic derangements, ultimately increasing the risk of many pathologies such as diabetes, cardiovascular disease, pulmonary embolism, cancers, low back pain, osteoarthritis and disability . Nonetheless, as weight gain is also commonplace during leave periods , it is reasonable to hypothesize that prolonged shelter-in-place ordinances will predispose to weight gain, an aspect magnified by the unhealthy dietary habits that very frequently accompany prolonged television viewing . Some specific measures should be recommended to people forced into a prolonged indoor stay, which would include caloric restriction through hypocaloric diets (encompassing also reduced portion size), reduction of total fat content, low-carbohydrate and high-protein foods, combined with increased intake of dietary fiber .
As COVID-19 is characterized by considerable derangement of the immune response, especially involving and injuring helper and suppressor T cells , a diet enriched with immunomodulatory foods such as pro- and pre-biotics and some vitamins (i.e. vitamin A, C and D) may also be advisable , .
Prolonged indoor stay is unavoidably accompanied by longer time spent watching television, online gaming or social networking, thus potentially worsening behavioral (i.e. internet, screen, or television) addiction disorders. The most common side effects encompass psychological disturbances (e.g. sleep deprivation, self-harm), neurological complications (e.g. eye strain, headache), musculoskeletal disorders (i.e. low back pain, carpal tunnel syndrome) ,  as well as increased risk of immobility-related venous thrombosis (i.e. the so-called e-thrombosis) . Remedies for this problem are more challenging to identify than those for managing the classic forms of behavioral addiction disorders, as a pre-existing organic cause (e.g. psychological vulnerability, psychoticism) is mostly lacking during prolonged lockdowns. The most effective measures would hence encompass a controlled and balanced usage of electronic devices, the adoption of external stoppers (events or activities persuading the user to log off), software programs controlling user’s time and development of inventories to track personal activities .
Insufficient sunlight exposure is another obvious consequence of prolonged indoor stay, which would then be accompanied by reduced level of circulating vitamin D [25-hydroxycholecalciferol; 25(OH)D]. It has now been established that sunlight exposure [especially to ultraviolet B (UVB) light] is the major limiting step in the endogenous generation of vitamin D, whereby sunlight mediates the conversion of precholecalciferol (previtamin D3) into cholecalciferol (vitamin D3), which is then converted into 25(OH)D by the liver enzyme vitamin D 25-hydroxylase . Several lines of evidence now attest that vitamin D not only is essential for bone health , but may also produce a vast array of pleiotropic (beneficial) effects, including lowering the risk of developing pathologies such as cardiovascular and autoimmune diseases, cancer, allergy and asthma, mental disorders, metabolic syndrome and diabetes, among others . The intricate interplay of vitamin D with immune system and infectious diseases is another important aspect, which has been the focus of many recent studies. Vitamin D receptors are highly expressed by many immune cells, including monocytes, and T and B lymphocytes . As the function of these cells is modulated by vitamin D, deficiency in this hormone is frequently associated with increased susceptibility to, and severity of, many infectious diseases . In particular, some recent studies provided credible evidence that subjects with vitamin D deficiency may be at significantly higher risk of developing respiratory tract infections . As SARS-CoV-2 is a coronavirus primarily causing a respiratory viral infection , vitamin D insufficiency due to inadequate sunlight may occur, especially in those countries where food fortification has not been introduced . As such, guidelines preventing the risk of vitamin D insufficiency seem advisable. Increased vitamin D intake can be achieved either by administering vitamin D as a dietary supplement (carefully weighing the risk of causing toxicity from hypervitaminosis D) or enriching the diet with foods that have a relatively high content of vitamin D, such as fatty fish, cod liver oil and egg yolks .
As the outbreak progresses with an increasing number of countries implementing restrictive measures, the number of people isolated at home increases in parallel. It is now established that social isolation must be regarded as a primary public health concern in the elderly, as it amplifies the burden of neurocognitive, mental, cardiovascular and autoimmune problems, as well as depression and anxiety . Moreover, recent evidence has demonstrated that sedentary behaviors in the youth may also be an important cause of depression and anxiety . As such, self-isolation should be seen as a global healthcare and societal issue.
Besides the need to find some reliable and sustainable means for delivering adequate amounts of groceries and essential medicines to those who may be unable to leave their homes autonomously during prolonged lockdown periods, counteracting the mounting burden of depression and anxiety becomes vital. Direct contact with relatives and friends is unfeasible where very restrictive measures have been applied, such that other forms of social contact should be urgently established for alleviating the unfavorable psychological consequences. This would also enable the timely identification of any potential health deteriorations, especially among individuals with pre-existing diseases. The obvious solutions to all these problems encompass a reinforcement of social care measures, as well as more frequent use of smartphones or online contacts, which shall be made available to those who lack sufficient economic resources.
As the COVID-19 outbreak continues its seemingly unstoppable course, and social distancing becomes the norm worldwide at least until a vaccine against SARS-CoV-2 becomes available, we are strongly persuaded that nationwide lockdowns are a kind of “necessary evil” for preventing an otherwise wide-reaching disaster. It can be reasonably estimated that COVID-19 may kill over 50 million people around the world if appropriate restrictive measures are not urgently established , thus potentially causing more causalities than the notorious Spanish (years 1918–1920), Asian (years 1957–1958) and swine (years 2009–2010) flu pandemics combined . As social distancing and homestay remain the most effective restrictive measures to stop the exponential growth of this contagion, efficient remedies must be identified and readily put into action to prevent the risk of developing unwarranted health consequences from prolonged indoor gatherings during nationwide lockdowns.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Research funding: None declared.
Employment or leadership: None declared.
Honorarium: None declared.
Competing interests: Authors state no conflict of interest.
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