Giuseppe Lippi , Brandon M. Henry , Chiara Bovo and Fabian Sanchis-Gomar

Health risks and potential remedies during prolonged lockdowns for coronavirus disease 2019 (COVID-19)

De Gruyter | Published online: April 7, 2020


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) [1], [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 [3]. 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) [4]. Some additional vehicles of potential contagion have been identified (e.g. direct contact with infected environmental or biological materials such as feces or saliva) [5], [6], [7], though respiratory droplets remain the largest source of contagion.

Figure 1: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) propagation by droplets.

Figure 1:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) propagation by droplets.

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 [8]. These numbers are inevitably destined to grow as definitive vaccines and cures for COVID-19 are unlikely to be identified soon [9]. As such, a combination of contact tracing and social isolation seems to be the most effective strategy to control the COVID-19 outbreak [10], 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 [11], [12].

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 [13]. This strategy has been proven effective for containing the COVID-19 outbreak in China, also limiting the exportation of infected cases outside the country [14], [15]. 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.

Table 1:

Health risks and potential remedies during prolonged nationwide lockdown for coronavirus disease 2019 (COVID-19).

Risk factor Most relevant health consequences Remedies
Physical inactivity – Osteoporosis

– Diabetes

– Cardiovascular disease

– Cancer

– Dementia
– 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

– Cancer

– Low back pain

– Osteoarthritis

– Disability
– 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

– E-thrombosis
– 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

– Anxiety

– Misidentification of health deterioration
– Delivering groceries and essential medicines

– Reinforce social care measures

– More frequent contacts with smartphone or social media

Physical inactivity

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 [16]. The important biological and metabolic adaptations would hence translate into a considerable higher risk of developing osteoporosis [17], diabetes [18], cardiovascular disease [19], cancer [20], dementia [21] as well as overweight/obesity [22], 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 [23].

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 [24]. 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 [25], 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 [26]. 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 [27], [28]. 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 [29]. 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 [30]. 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 [31], preventing any additional strain of care due to unwarranted injuries on an already exhausted system is vital.

Weight gain

The risk of weight gain, up to developing overweight or obesity, is one of the most significant implications of physical inactivity [22]. Overweight and obesity, defined by the WHO as a body mass index (BMI) ≥25 and ≥30 kg/m2, respectively [32], 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 [33]. Nonetheless, as weight gain is also commonplace during leave periods [34], 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 [35]. 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 [36].

As COVID-19 is characterized by considerable derangement of the immune response, especially involving and injuring helper and suppressor T cells [37], 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 [38], [39].

Behavioral addiction disorders

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) [40], [41] as well as increased risk of immobility-related venous thrombosis (i.e. the so-called e-thrombosis) [42]. 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 [40].

Insufficient sunlight exposure

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 [43]. Several lines of evidence now attest that vitamin D not only is essential for bone health [44], 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 [45]. 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 [46]. 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 [47]. 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 [48]. As SARS-CoV-2 is a coronavirus primarily causing a respiratory viral infection [49], vitamin D insufficiency due to inadequate sunlight may occur, especially in those countries where food fortification has not been introduced [50]. 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 [51].

Social isolation

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 [52]. Moreover, recent evidence has demonstrated that sedentary behaviors in the youth may also be an important cause of depression and anxiety [53]. 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 [2], thus potentially causing more causalities than the notorious Spanish (years 1918–1920), Asian (years 1957–1958) and swine (years 2009–2010) flu pandemics combined [54]. 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.


1. Coronaviridae Study Group of the International Committee on Taxonomy of V. The species Severe acute respiratory syndrome-related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2. Nat Microbiol 2020;5:536–44. Search in Google Scholar

2. Lippi G, Sanchis-Gomar F, Henry BM. Coronavirus disease 2019 (COVID-19): the portrait of a perfect storm. Ann Transl Med 2020; doi: 10.21037/atm.2020.03.157. Search in Google Scholar

3. Guo YR, Cao QD, Hong ZS, Tan YY, Chen SD, Jin HJ, et al. The origin, transmission and clinical therapies on coronavirus disease 2019 (COVID-19) outbreak – an update on the status. Mil Med Res 2020;7:11. Search in Google Scholar

4. Atkinson J, Chartier Y, Pessoa-Silva CL, Jensen P, Li Y, Seto WH, editors. Natural ventilation for infection control in health-care settings. Geneva: World Health Organization; 2009. Annex C, Respiratory droplets. Available at: Last accessed: March 25, 2020. Search in Google Scholar

5. van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med 2020; doi: 10.1056/NEJMc2004973. Search in Google Scholar

6. Zhang J, Wang S, Xue Y. Fecal specimen diagnosis 2019 novel coronavirus-infected pneumonia. J Med Virol 2020; doi: 10.1002/jmv.25742. Search in Google Scholar

7. To KK, Tsang OT, Chik-Yan Yip C, Chan KH, Wu TC, Chan JM, et al. Consistent detection of 2019 novel coronavirus in saliva. Clin Infect Dis 2020; doi: 10.1093/cid/ciaa149. Search in Google Scholar

8. World Health Organization. Coronavirus disease 2019 (COVID-19) Situation Report – 65. Available at: Last accessed: March 25, 2020. Search in Google Scholar

9. Han Q, Lin Q, Jin S, You L. Coronavirus 2019-nCoV: a brief perspective from the front line. J Infect 2020;80:373–7. Search in Google Scholar

10. Hellewell J, Abbott S, Gimma A, Bosse NI, Jarvis CI, Russell TW, et al. Feasibility of controlling COVID-19 outbreaks by isolation of cases and contacts. Lancet Glob Health 2020;8:e488–96. Search in Google Scholar

11. Babic B, Gerke S, Evgeniou T, Cohen IG. Algorithms on regulatory lockdown in medicine. Science 2019;366:1202–4. Search in Google Scholar

12. MacIntyre CR. On a knife’s edge of a COVID-19 pandemic: is containment still possible? Public Health Res Pract 2020:30. pii: 3012000. Search in Google Scholar

13. The Brussels Time. Coronavirus: nearly a billion people in lockdown. Available at: Last accessed: March 25, 2020. Search in Google Scholar

14. Lau H, Khosrawipour V, Kocbach P, Mikolajczyk A, Schubert J, Bania J, et al. The positive impact of lockdown in Wuhan on containing the COVID-19 outbreak in China. J Travel Med 2020; doi: 10.1093/jtm/taaa037. Search in Google Scholar

15. Wells CR, Sah P, Moghadas SM, Pandey A, Shoukat A, Wang Y, et al. Impact of international travel and border control measures on the global spread of the novel 2019 coronavirus outbreak. Proc Natl Acad Sci USA 2020; doi: 10.1073/pnas.2002616117. Search in Google Scholar

16. Lippi G, Henry MB, Sanchis-Gomar F. Physical inactivity and cardiovascular disease at the time of coronavirus disease 2019 (COVID-19). Eur J Prev Cardiol 2020; in press. Search in Google Scholar

17. Castrogiovanni P, Trovato FM, Szychlinska MA, Nsir H, Imbesi R, Musumeci G. The importance of physical activity in osteoporosis. From the molecular pathways to the clinical evidence. Histol Histopathol 2016;31:1183–94. Search in Google Scholar

18. Bhaskarabhatla KV, Birrer R. Physical activity and diabetes mellitus. Compr Ther 2005;31:291–8. Search in Google Scholar

19. Lippi G, Sanchis-Gomar F. An estimation of the worldwide epidemiologic burden of physical inactivity-related ischemic heart disease. Cardiovasc Drugs Ther 2020;34:133–7. Search in Google Scholar

20. Sanchis-Gomar F, Lucia A, Yvert T, Ruiz-Casado A, Pareja-Galeano H, Santos-Lozano A, et al. Physical inactivity and low fitness deserve more attention to alter cancer risk and prognosis. Cancer Prev Res (Phila) 2015;8:105–10. Search in Google Scholar

21. Lee J. The relationship between physical activity and dementia: a systematic review and meta-analysis of prospective cohort studies. J Gerontol Nurs 2018;44:22–9. Search in Google Scholar

22. Pietilainen KH, Kaprio J, Borg P, Plasqui G, Yki-Jarvinen H, Kujala UM, et al. Physical inactivity and obesity: a vicious circle. Obesity (Silver Spring) 2008;16:409–14. Search in Google Scholar

23. Mok A, Khaw KT, Luben R, Wareham N, Brage S. Physical activity trajectories and mortality: population based cohort study. Br Med J 2019;365:l2323. Search in Google Scholar

24. World Health Organization. Physical activity and adults. Available at: Last accessed: March 25, 2020. Search in Google Scholar

25. Lazzerini M, Putoto G. COVID-19 in Italy: momentous decisions and many uncertainties. Lancet Glob Health 2020; doi: 10.1016/S2214-109X(20)30110-8. Search in Google Scholar

26. Yuen KS, Ye ZW, Fung SY, Chan CP, Jin DY. SARS-CoV-2 and COVID-19: the most important research questions. Cell Biosci 2020;10:40. Search in Google Scholar

27. McKenzie DC. Respiratory physiology: adaptations to high-level exercise. Br J Sports Med 2012;46:381–4. Search in Google Scholar

28. Aliverti A. The respiratory muscles during exercise. Breathe (Sheff) 2016;12:165–8. Search in Google Scholar

29. Sullivan AN, Lachman ME. Behavior change with fitness technology in sedentary adults: a review of the evidence for increasing physical activity. Front Public Health 2016;4:289. Search in Google Scholar

30. Maffulli N, Del Buono A, Oliva F, Giai Via A, Frizziero A, Barazzuol M, et al. Muscle injuries: a brief guide to classification and management. Transl Med UniSa 2015;12:14–8. Search in Google Scholar

31. Fisher D, Heymann D. Q&A: the novel coronavirus outbreak causing COVID-19. BMC Med 2020;18:57. Search in Google Scholar

32. World Health Organization. Obesity and overweight. Available at: Last accessed: March 25, 2020. Search in Google Scholar

33. Djalalinia S, Qorbani M, Peykari N, Kelishadi R. Health impacts of obesity. Pak J Med Sci 2015;31:239–42. Search in Google Scholar

34. Diaz-Zavala RG, Castro-Cantu MF, Valencia ME, Alvarez-Hernandez G, Haby MM, Esparza-Romero J. Effect of the holiday season on weight gain: a narrative review. J Obes 2017;2017:2085136. Search in Google Scholar

35. Harris JL, Bargh JA. Television viewing and unhealthy diet: implications for children and media interventions. Health Commun 2009;24:660–73. Search in Google Scholar

36. Astrup A. Dietary management of obesity. JPEN J Parenter Enteral Nutr 2008;32:575–7. Search in Google Scholar

37. Qin C, Zhou L, Hu Z, Zhang S, Yang S, Tao Y, et al. Dysregulation of immune response in patients with COVID-19 in Wuhan, China. Clin Infect Dis 2020; doi: 10.1093/cid/ciaa248. Search in Google Scholar

38. Wichers H. Immunomodulation by food: promising concept for mitigating allergic disease? Anal Bioanal Chem 2009;395:37–45. Search in Google Scholar

39. Azad MA, Sarker M, Wan D. Immunomodulatory effects of probiotics on cytokine profiles. Biomed Res Int 2018;2018:8063647. Search in Google Scholar

40. Cash H, Rae CD, Steel AH, Winkler A. Internet addiction: a brief summary of research and practice. Curr Psychiatry Rev 2012;8:292–8. Search in Google Scholar

41. World Health Organization. Public health implications of excessive use of the internet, computers, smartphones and similar electronic devices. Geneva, Switzerland: WHO Press, World Health Organization, 2014. Search in Google Scholar

42. Lippi G, Mattiuzzi C, Favaloro EJ. e-thrombosis: epidemiology, physiopathology and rationale for preventing computer-related thrombosis. Ann Transl Med 2018;6:344. Search in Google Scholar

43. Lippi G, Cervellin G, Danese E. Indoor tanning a Gianus Bifrons: vitamin D and human cancer. Adv Clin Chem 2018;83:183–96. Search in Google Scholar

44. Lippi G, Targher G. Are we overrating the extra-skeletal benefits of oral vitamin D supplementation? Ann Transl Med 2019;7:499. Search in Google Scholar

45. Targher G, Pichiri I, Lippi G. Vitamin D, thrombosis, and hemostasis: more than skin deep. Semin Thromb Hemost 2012;38:114–24. Search in Google Scholar

46. Prietl B, Treiber G, Pieber TR, Amrein K. Vitamin D and immune function. Nutrients 2013;5:2502–21. Search in Google Scholar

47. Aranow C. Vitamin D and the immune system. J Investig Med 2011;59:881–6. Search in Google Scholar

48. Beard JA, Bearden A, Striker R. Vitamin D and the anti-viral state. J Clin Virol 2011;50:194–200. Search in Google Scholar

49. Moriyama M, Hugentobler WJ, Iwasaki A. Seasonality of respiratory viral infections. Annu Rev Virol 2020; doi: 10.1146/annurev-virology-012420-022445. Search in Google Scholar

50. Kennel KA, Drake MT, Hurley DL. Vitamin D deficiency in adults: when to test and how to treat. Mayo Clin Proc 2010;85:752–7; quiz 7–8. Search in Google Scholar

51. Pilz S, Marz W, Cashman KD, Kiely ME, Whiting SJ, Holick MF, et al. Rationale and plan for vitamin D food fortification: a review and guidance paper. Front Endocrinol (Lausanne) 2018;9:373. Search in Google Scholar

52. Armitage R, Nellums LB. COVID-19 and the consequences of isolating the elderly. Lancet Public Health 2020; doi: 10.1016/S2468–2667(20)30061-X. Search in Google Scholar

53. Belair MA, Kohen DE, Kingsbury M, Colman I. Relationship between leisure time physical activity, sedentary behaviour and symptoms of depression and anxiety: evidence from a population-based sample of Canadian adolescents. BMJ Open 2018;8:e021119. Search in Google Scholar

54. Saunders-Hastings PR, Krewski D. Reviewing the history of pandemic influenza: understanding patterns of emergence and transmission. Pathogens 2016:5. pii: E66. Search in Google Scholar

Received: 2020-03-26
Accepted: 2020-03-26
Published Online: 2020-04-07
Published in Print: 2020-05-26

©2020 Walter de Gruyter GmbH, Berlin/Boston