How can the upcoming cold weather affect the COVID-19 pandemic? Should we prepare for something unprecedented?

By ensuring you're Vitamin D sufficient, something you should be especially concerned about if you are elderly and/or have dark skin. 2 in 5 Americans are Vitamin D Insufficient and that number is higher for certain demographics that are older and have more melanin in their skin especially with a low UV index typical of winter weather. A National Center for Health Statistics study found that 41.6% of Americans including 82% of blacks and 70% of hispanics have insufficient vitamin D serum concentrations of less than 20 nano-grams/mL. Vitamin D sufficiency is not only inversely correlated with melanin but also education, obesity and hypertension. The inverse correlation with melanin means it takes longer to synthesize the same amount of Vitamin D from the same UV Index exposure and air temperature. For example, Taksler and colleagues, publishing in Public Health Nutrition, found that it would take fair skinned whites 31 minutes to synthesize 600 international units of D3 in Atlanta in January with an average UV index of 2.5 and temperature of 52 degrees Fahrenheit. It would take mestizos 1 hour and 9 minutes (2.2x longer) and blacks 2 hours and 33 minutes, almost 5x longer, to synthesize the same amount of vitamin D under the same conditions. Across all geographical locations in the U.S., whites have the highest average January adjusted vitamin D serum levels (23.75 ng/mL) and blacks have the lowest (13.21 ng/mL). The authors note that the racial gap in vitamin D serum concentrations is a potential contributor to disparities in disease incidence, severity and morality yet this is never discussed in the mainstream press. A comparison of 2007 mortality ratios for black and white Americans across several diseases was found to closely match vitamin D serum level outcome ratios between 16 ng/mL and 26 ng/mL; the year round population average for blacks and whites. Grant and Peiris, publishing in the Journal of the American Medical Directors Association, found that the mortality ratios for blacks and whites for breast cancer, colorectal cancer, cardiovascular disease and all cause mortality in 2006 were 1.34, 1.43, 1.29, and 1.26 respectively while the mortality ratios for 16 ng/mL vs. 26 ng/mL concentrations of vitamin D were 1.26, 1.44, 1.27, and 1.26 for the same diseases and all cause mortality. A retrospective cohort study, using data from the third National Health and Nutrition Examination Survey conducted between 1988-94 (n = 15,363), found that vitamin D serum concentrations in the lowest quartile of less than 18 ng/mL (average 13.9 ng/mL ) are associated with a 40% higher age and sex adjusted cardiovascular mortality rate. Another retrospective cohort study,using the same survey data (n = 15,772), found that vitamin D deficiency is associated with a 2x higher risk of dying from colorectal cancer and that it attenuated the colorectal cancer mortality risk of being black by 40% independent of SES and behavioral risk factors. Almost 58% of black participants in this sample were vitamin D deficient compared to only 16% of white participants.

As I noted in a prior post, Vitamin D deficiency also increases the risk of acute respiratory infections that crop up in the winter while vitamin D supplementation mitigates the risk for vitamin D insufficient people especially for the most severe outcomes. A systematic review of 38 studies found that vitamin D supplementation reduced the risk of ICU admission and intubation by 62% following a SARS-COV-2 infection and the relative risk of COVID-19 mortality by 65%. A meta-analysis of 23 studies (n= 2,692) found that calcifediol serum deficiency doubled the relative risk of severe disease following SARS-COV-2 infection in 17 studies and mortality in 13 studies. As I mentioned in Vitamin D as a COVID-19 Prophylaxis, deficiency and supplementation can also increase or decrease the risk of SARS-COV-2 infection itself. A systematic review of 7 RCTs (PRISMA Study) found that vitamin D supplementation reduced the relative risk of infection by up to 80% among healthcare workers. A retrospective cohort study of VA patients (n = 465,428), published in Nature, found a more modest 28% reduced risk of infection among patients who supplement vitamin D3 with the benefit plateauing at serum concentrations of 40 ng/mL. The authors estimate that D3 supplementation could have resulted in 4 million fewer COVID19 cases and 116,000 fewer COVID19 deaths in 2020: a 33% decrease in mortality. A systematic review of 43 RCTs published in the Lancet found that vitamin D supplementation has a statistically significant protective effect, compared to placebo controls, as a daily regimen of 400-1,000 international units (10-25 ug) but not as a weekly or monthly bolus and not for participants with an existing pulmonary disease and unlike modRNA transfection the immune boost of vitamin D sufficiency does not “wane” within a few months.