Most people don't get enough vitamin D. As one of the few "vitamins" that the body can produce on its own, vitamin D is actually a secosteroid hormone that is synthesized in the skin through exposure to sunlight. It is well-known for its role in calcium absorption and bone health, but also essential for immune system functioning, reducing inflammation, and preventing chronic disease. Research shows that vitamin D supplementation reduces the risk of viral and acute respiratory infection, suggesting that it can play a critical role during the pandemic in reducing the incidence and severity of COVID-19, as well as mortality from the disease.
More than a billion people worldwide are estimated to be deficient or insufficient in vitamin D, including 40-50% of the U.S. population. Vitamin D deficiency is a health concern in almost every country in the world, across all age groups. It is seen in countries at low latitudes near the equator that experience higher amounts of sunshine, as well as in countries where foods are commonly fortified with vitamin D.
Several factors contribute to inadequate vitamin D levels: decreased sun exposure (from seasonal changes, living in northern latitudes, working indoors, or increased sunscreen usage), skin pigmentation (people with darker skin and more melanin content produce less vitamin D), aging (vitamin D synthesis decreases as our skin becomes thinner), obesity (excess vitamin D is stored in accumulated fat, but only becomes available through weight loss), and dietary intake (not getting enough vitamin D from natural sources or fortified foods).
Vitamin D and qi are closely related. As the "sunshine vitamin," vitamin D is produced when our skin is exposed to strong sunlight and UV rays. In Eastern medicine, qi is the energetic force found in all living things – we acquire it from the fresh air and sunshine in our environment, as well as from our diet and physical activity. It is not coincidental that the symptoms of "qi deficiency" described in Chinese Medicine are similar to those seen with vitamin D deficiency: weakness, fatigue, muscle pain, low immunity, and recurring infections.
The role of vitamin D in supporting our immune system is critical to its ability to protect against COVID-19. Vitamin D enhances cellular immunity and microbial response, decreases susceptibility to infection, and protects against excessive inflammation by suppressing the cytokine storm seen in severe cases of COVID-19. Recent studies suggest that people with low levels of vitamin D have an increased risk of getting COVID-19, as well as increased severity of the disease.
Population groups with the highest risk of severe COVID-19 match those with the highest risk for severe vitamin D deficiency – males, the elderly, obese individuals, and people of color with melanin-rich skin. COVID-19 infection rates may also correlate to seasonality, with higher infection rates seen during the winter, when population levels of vitamin D are lower. Additional research shows that countries with higher dietary intake of vitamin D have lower mortality rates from COVID-19 than adjacent countries.
Vitamin D deficiency can be easily corrected with adequate sunlight exposure, dietary intake, and supplementation. While protecting your skin from sun damage and cancer is important, moderate amounts of sun exposure (5 to 15 minutes, 2 to 3 times a week) are beneficial for increasing your vitamin D levels. Note that even sunscreens with a SPF 15 rating can decrease vitamin D production in the skin by 99%.
It is also helpful to get your blood checked every year or two, to determine your baseline vitamin D levels. The optimal level of 25-hydroxy-vitamin D is 35-50 ng/mL. Natural dietary sources of vitamin D include fatty fish (e.g. salmon, tuna, herring, mackerel, and cod), cod liver oil, oysters, egg yolks, and mushrooms that have been exposed to sunlight or UV radiation. Many dairy and soy products are also fortified with vitamin D.
In terms of supplements, Vitamin D3 is more easily absorbed by the body than D2. Scientific consensus suggests a range of 1,000-2,000 IU/day of vitamin D as a preventative for COVID-19, and daily supplementation at that level is safe from the risk of toxicity. As a low cost and supportive measure, there is nothing to be lost by supplementing with vitamin D during the pandemic, but much to be gained.
Aranow, C., 2011. Vitamin D and the immune system. Journal of Investigative Medicine, 59(6):881-886.
Benskin, L.L., 2020. A basic review of the preliminary evidence that COVID-19 risk and severity is increased in vitamin D deficiency. Frontiers in Public Health, 8:513.
Holick, M.F., 2010. The vitamin D deficiency pandemic: a forgotten hormone important for health. Public Health Reviews, 32(1):267-283.
Martineau, A.R., D.A. Jolliffe, R.L. Hooper, et al. 2017. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ:356.
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