IMPORTANT: if supplementing with Vitamin D, it is vital to take in adequate amounts of Vitamin K2 and magnesium and Vitamin A. Most of the population is deficient in magnesium and Vitamin D and highly deficient in Vitamin K2.
Vitamin D is not well understood by the public. It is sort of a vitamin and sort of a hormone, but acts much more like a hormone, regulating a wide variety of processes in the body, including the immune system. While its role requires a great deal more research, it’s clear that it is critically important to the body and performs many functions.
All sorts of things are sub-optimal in the body with low Vitamin D.
There is a strong inverse correlation between Vitamin D levels and death from COVID-19, meaning that low Vitamin D in the body is associated with higher rates of death from COVID-19, and higher levels of Vitamin D are associated with lower rates of death.
Correlation is not causation. For example, wearing clothes is almost perfectly correlated to dying in a car crash. Does wearing clothes cause you to die in a car crash?
Therefore, Vitamin D might not be the driving factor, but merely an association (correlation).
However, Vitamin D is known to help regulate the immune system, so low Vitamin D levels are are at best a bad idea in general, and a very bad situation with COVID-19 in the wild.
Vitamin D (VD) deficiency is a major public health problem worldwide. In spite of its high prevalence, particularly among elderly people, VD deficiency is still underestimated by many physicians. Increasingly, VD deficiency is associated with several known geriatric syndromes.
... Vitamin D (VD) or calciferol, a fat-soluble vitamin, is chemically classified as a steroid. There are two main sources of VD: the dietary and the endogenous synthesis. Vitamin D2 (ergocalciferol) is obtained from plants. While a small quantity of Vitamin D3 (cholecalciferol) is provided by animal-derived food, the main natural VD source is skin synthesis during sunlight exposure (exposure to ultraviolet B).
...VD also has noncalcemic and nonskeletal effects. Several studies have reported an inverse association between VD levels and the risk of oral, gastrointestinal, urinary, ocular, and respiratory infections. In addition, VD is widely known for its potent immunomodulatory role since a strong relationship between VD deficiency and the prevalence of autoimmune disorders was observed.
... VD deficiency is a pandemic nutritional problem throughout the world. Interestingly, VD deficiency has been reported even in some equatorial countries, where people can get adequate sun exposure. It has been reported that more than one-third of human adults have low 25(OH)D levels. In addition, VD deficiency is often severe and significantly more seen in elderly people.
These outcomes demonstrate that VD deficiency is a public health problem, predominately in the elderly. Lack of physical activities and sun exposure are most likely the key reasons behind this relevant VD deficiency in elderly people. In addition, VD synthesis in the skin is reported to be widely diminished in the elderly.
Who is dying from COVID-19?
Which groups die the most from COVID-19? Mainly the elderly, but also disproportionately more people with dark skin, people with diabetes, etc. These groups all are likely to have low Vitamin D levels because the primary means by which Vitamin D is generated is sunlight on the skin. The elderly and people with dark skin are much less likely to get much sunlight. Ditto for prisoners and other groups that are dying at higher rates.
Should you take Vitamin D to ward off COVID-19?
Who can say at this point? But low Vitamin D almost certainly will not work in your favor.
For many years I have made it a point even in winter to try and get 20 minutes of sun every day, and on my 2+ month self-isolating trip here in spring of 2020 with COVID-19, I made it a point of a minimum of 30 minutes on back or chest/abdomen.
You can supplement with Vitamin D precursor cholecalciferol; I use YounGlo Research Vitamin D3 @AMAZON though I might switch to Nordic Naturals Vitamin D3 @AMAZON (Nordic Naturals is a top-flight brand in general).
I have taken up to 50,000 IU per day with no ill effects, but typically I take 10,000 IU per day in the winter, 5000 IU or none at all when I am getting plenty of sun in the summer. Note that Vitamin D as sold is generally a precursor chemical which the body uses.
The natural and IMO best way to raise your Vitamin D level is to get 20-30 minutes of sun on your bare skin every day (no sunblock). It is my understanding that it takes the body 15 minutes to get rolling on Vitamin D synthesis, so 5-10 minutes doesn’t cut it. Also, it may take substantially more exposure to get adequate synthesis for some people, depending on skin tone, genetics, and diet—so have a blood tests for Vitamin D levels in winter in particular (and IMO anything less than DOUBLE the minimum level is grounds for increasing it).
Less sun-time for the fair-skinned, more for dark skin, but do not let your skin redden or burn. I suggest protecting the face and upper arms, and letting the back or chest/abdomen soak up those rays and since those are large in area, you get maximum exposure in minimum time. In other words, take off your shirt and/or pants and sunbathe. DO NOT USE SUNSCREEN for purposes of Vitamin D synthesis.
Yes, sunlight in moderation without sunscreen is healthy and necessary in spite of the claims made by the medical establishment (dermatologists) who see only skin and not a complete human body. Whole body health is the ticket, and sunlight is part of that. Of course, a healthy diet is essential for the body and contributes to a synergistic whole. My guess is that many cancers stem from swiss-cheesed approaches to health, not from some inherent danger from moderate sunlight. This is the constant danger of one isolated branch of medicine (dermatology) failing to consider the whole creature.
If you do use sunscreen, stick to zinc oxide, which blocks (reflects away) all types of UV rays. My prediction is that in 10-20 years, it will be shown that most sunscreens contribute to skin cancer by suppressing the UV rays that are needed by the body for Vitamin D production and allowing through the UV rays that are associated with skin cancer.