Vitamin D and Covid

Vitamin D is known to be important for the health of the immune system, particularly immunity to respiratory infections like colds, flu, pneumonia and Covid-19. It can help resist infection and make the often-fatal cytokine storm that can accompany lung infections less likely. Vitamin D is also essential for calcium absorption and therefore strong bones.

Vitamin D comes from three sources: food, UVB radiation from the sun or tanning beds and vitamin supplements. It is hard to get enough from food; many people, particularly those who live a long way from the equator get little from the sun, particularly in winter; and most people don’t use tanning beds or take vitamin D supplements.

The consequence is that many people are deficient in vitamin D and thus more prone to respiratory infections. I am suggesting that ensuring that everyone gets sufficient vitamin D could help significantly in reducing the incidence of Covid-19 and the resulting death toll.

Evidence Implicating Vitamin D Deficiency in Susceptibility to Covid

For most people, the major source of vitamin D is sunshine. But, as will be explained below, it is impossible to get significant vitamin D when the sun is less than about 40° above the horizon. This means that many people in Europe and North America get no vitamin D from the sun in winter. It is estimated that around half the population of these areas are deficient by late winter.

In the early stages of the Covid pandemic, it was late winter in the northern hemisphere and late summer in the southern hemisphere. Countries in Europe and North America had a much greater incidence of the disease than countries in the southern hemisphere.

By May, when it is possible to get a lot more vitamin D from the sun, infection and death rates in Europe and North America were dropping significantly despite the easing of lock-down restrictions.

In people with dark skin, the melanin absorbs much of the UVB before it can produce vitamin D. In Africa and other tropical places, this isn’t a problem, because people tend to spend a lot of time outdoors when the sun is high in the sky, their melanin allowing them to do so without getting sunburnt. People with dark skin living in Europe and North America, however, don’t tend to get any more sun than their lighter-skinned counterparts and, as they produce a lot less vitamin D from a given exposure, are more likely to be vitamin D deficient.

In both Europe and North America, people with dark skin are significantly more likely to come down with Covid-19 than lighter-skinned people, and, if they do come down with it, are significantly more likely to get seriously ill or die.

Countries in Sub-Saharan Africa all had cases of Covid-19 in the early stages of the pandemic, but the disease did not spread in these countries the way it did in Europe and North America. This is despite the fact that medical facilities would be much less adequate in Africa and lock-down would be harder to maintain.

Countries in North Africa and the Middle East do have higher rates of infection than Sub-Sharan African countries, despite their abundant sunshine. This may be related to the way people in those countries tend to dress. Many people, particularly women, rarely expose their skin to the sun.

This picture suggests that vitamin D might be a significant factor in the susceptibility of different populations to Covid-19. However, it has gone almost without mention in news reports, health advice and papers attempting to explain the epidemiology. The over-representation of people of African origin amongst the sick and dead in both America and Europe is almost always explained in social terms (poverty, poor diet, lack of access to medical facilities etc.), with barely ever a mention that vitamin D deficiency could be a factor.

Getting More Vitamin D

If it is true that susceptibility to Covid and other respiratory infections is related to vitamin D levels, then it might be worth trying to ensure that everyone gets sufficient vitamin D. Publicised advice to get more sunshine and/or to take vitamin D supplements would go a long way to ensuring this.

If the relation is real, then this could make less people susceptible and thus reduce the rate of spread and the rate of death. If the relation is not real, then very little has been lost by taking such action. One would think it worth a try. The economic damage from the pandemic world-wide is many trillions of dollars. Providing everyone with free vitamin D supplements may save much more economic damage and heartache than it costs.

Even if it didn’t help with Covid, it may well help with colds and flus, osteoporosis etc.

How Much Vitamin D Do We Need?

The recommended dose of vitamin D is 400-800 IU (international units) per day. However, the body seems to suffer no ill effects from much higher doses and many authorities recommend about 4000 IU per day for an optimal immune system and good bone health.

Vitamin D stays in the system for a number of months. People with deficiencies have developed these over several months and need to build up their supply by getting several months supply. This might me an amount of the order of 50 000 to 200 000 IU.

Doses of this size are often given and seem to do no harm. The only harm from too much vitamin D seems to be hypercalcaemia (too much calcium in the blood) and this can arise if doses of about 50 000 IU per day are taken regularly for several months. Making up for a deficiency with say 10 000 IU per day for a week or two, then taking an ongoing dose of 4 000 IU per day might do a lot of good and, by all accounts, will have no adverse effects.

Getting Vitamin D from Food

As mentioned, it is difficult to get enough vitamin D from food. Living on wild-caught Salmon and irradiated mushrooms may do the job, but most people don’t do that. It seems that mankind evolved to get their vitamin D from the sun almost exclusively.

We evolved in Africa and populations who spread to higher latitudes changed from black to white because the darker people couldn’t get enough vitamin D and so died out. As far as we know, that’s the only reason we turned white.

Getting Vitamin D from the Sun

It is quite easy for fair-skinned people to get 4000 IU of vitamin D or more per day when the sun gets high in the sky. However, in winter in higher latitudes, it can be difficult or impossible to get even 400 IU. Vitamin D is produced by UVB radiation. UVB is strongly absorbed by the atmosphere, particularly by ozone in the stratosphere. Even when the sun is overhead, only about 0.6% of the UVB that arrives at the top of the atmosphere reaches the ground. This 0.6%, though, is more than sufficient for humans to get a totally satisfactory dose of vitamin D.

However, because the absorption rate is high, when the sun is lower in the sky, a lot less UVB reaches the ground. When the sun is 30° above the horizon, the light has to pass through twice the thickness of atmosphere (and ozone) and so only 0.6% of 0.6% of the UVB reaches the ground. If the sun is at an elevation of E° above the horizon, then the fraction of the UVB reaching the ground is given by 0.006^(cosec E°)

The table below presents this information in a more friendly form.

You may know how to calculate the elevation of the sun at local midday. If not, the formula is E = 90° – |s – λ|, where s is how far the sun is north of the equator and λ is your latitude (positive in the northern hemisphere, negative in the southern hemisphere). |s – λ| means the difference between s and λ, taken as positive.

s = 23.5 sin πt⁄6 where t is the time in months since 21st March. Calculated values are given in the table below to make it easier. You can interpolate between these values.

Note that these figures for vitamin D production are based on whole-body exposure perpendicular to the sun’s rays. Exposing just one’s face and hands while walking around in the sun would produce only a tenth or less of the above doses.

Also, the figures are approximate and probably on the optimistic side because UVB absorption depends on the water content of the air, pollution and other factors. Furthermore, they apply to people with fair skin. Skin with more melanin absorbs much of the UVB before it can produce vitamin D. People with black skin receive only a small fraction of the vitamin D that someone with fair skin would receive.

Note also, that UVA is not absorbed by the atmosphere anything like as much as UVB, so, although 4000 IU can be obtained in 40 minutes when the sun is at 40°, the amount of UVA received in that time could well be enough to cause sunburn.

All in all, it is easy for people who live in the tropics to get adequate vitamin D year-round. Though the current trend of avoiding exposure to the sun near midday can mean that even those in the tropics may not get enough vitamin D.

Many people living at higher latitudes cannot get adequate vitamin D from the sun in the winter months. For example, in London in December, the sun reaches a maximum elevation of only about 15° at midday making it impossible to get significant vitamin D. Apart from the low elevation of the sun, the frequency of cloud and the fact that the temperature tends to discourage people from stripping off and lying in the sun, compound the problem. [UVB doesn’t pass through glass, so sun bathing has to be outdoors.]

All in all, many Europeans and North Americans receive negligible vitamin D from the sun between October and March. It is possible to get sufficient vitamin D during the other months, as long as one is prepared to strip off and sun bake regularly around midday when the sun is at a sufficient elevation in the sky. The trouble is that many people are at work and indoors most days around that time and, even when they aren’t, the sun doesn’t always shine and many people are too ‘sun-aware’ to expose themselves to the sun anyway. The problem is exacerbated for people with dark skin who produce much less vitamin D from the same sun exposure.

It is thought that a major proportion of the population of countries in Europe and North America are deficient in vitamin D in winter and a significant number are deficient year-round. The great majority of people of African or southern-Asian descent in those countries would be deficient at least in winter.

Getting Vitamin D from Supplements

Vitamin D supplements are available from any chemist. 1000 IU is a common pill size. For people not getting enough sunshine, one to four pills per day would probably be optimal (after making up for any accumulated deficiency. As mentioned above, it seems that very much larger doses can be taken initially without ill effects. This might be 50 000 to 200 000 IU as a one-off dose or 10 000 IU per day for a week or two.

Conclusion

Unless one is confident of getting adequate vitamin D from the sun, it might be wise to take a supplement. This is particularly true while Covid-19 is around, but will probably continue to be true at other times to reduce the likelihood of flu, colds etc.

A public education campaign to make people aware of this would probably be worthwhile. A lot of air time has been given to staying at home, social distancing etc. But ensuring that everyone has adequate levels of vitamin D could be almost as beneficial.