Vitamin D, COVID-19, and Pregnancy: New Findings

Note: The Pregistry website includes expert reports on more than 2000 medications, 300 diseases, and 150 common exposures during pregnancy and lactation. For the topic Coronavirus, go here. These expert reports are free of charge and can be saved and shared.


Recently, on The Pulse, there was a nice review of vitamin D , explaining the importance of getting adequate vitamin D during pregnancy and wrapping up with the caveat that there’s no evidence that vitamin D will reduce your chances of getting COVID-19. Recently means April, about a month before I’m writing this post, and back in April there was indeed no evidence. But, in science and medicine, new data are always arriving and they can change the story. This is what happened in early May when a study was published that examined the blood concentrations of vitamin D in some 21 European countries. In blood, vitamin D is measured specifically as the chemical compound 25-hydroxyvitamin D. Tests for the concentration of this compound are performed routinely in blood samples from individuals and test results can be combined to reveal average vitamin D blood levels in populations, such as populations of countries, of age groups, of people of different ethnicities, genders, disease states, and so forth. Overall, the study found what the authors call “crude relationships between vitamin D levels and the number COVID-19 cases and especially the mortality caused by this infection.” Furthermore, the study revealed blood concentrations of vitamin D to be severely low, particularly among the elderly of Spain, Italy, and Switzerland. It just so happens that Spain and Italy have suffered both particularly high rates of COVID-19 and particularly high rates of critical complications and death among those who do develop COVID-19.

Vitamin D is not actually a vitamin, but rather a hormone, as it is something that your skin cells can make. To make vitamin D, your body starts with cholesterol, which gets modified through a series of chemical reactions. Along the way, your body needs ultraviolet (UV) radiation from the Sun. Consequently, the levels of vitamin D that build up in your bloodstream depend on factors that include your latitude (distance from the equator), your altitude, amount of time you spend outside, the time of day that you go outside, your skin type, and how much you cover your body with clothing, hats, shoes, and sunscreen. Getting enough vitamin D from sunlight can be tricky, because the same UV radiation that gives you vitamin D also causes skin cancer. Generally, it does not take much sunlight to generate a good amount of vitamin D, but the amount varies depending on your skin and geographic situation. As noted in the article cited above as well as other previous articles on The Pulse, it is also recommended that people, including pregnant women, take vitamin D supplements to assure that they will have adequate levels in their blood. The daily dosage of vitamin D that you should take during pregnancy is a topic that has been debated in recent years. Daily pregnancy multivitamin supplements typically include 600 international units and upward of that number, but of course women who get more vitamin D from sunlight, fish, and dairy products don’t need to get as much from supplements as women who avoid those sources of vitamin D.

Experts often classify skin according to what’s called the Fitzpatrick skin type system. In this system, there are six skin types. Type 1 is the lightest skin, the kind of skin that burns very easily and does not tan. When the comedian Woody Allen used to describe his own skin saying, “When I go to the beach, I don’t tan; I stroke,” he was referring to Fitzpatrick type 1. At the opposite end of the spectrum, type 6 skin is dark brown to black. Whereas people with type 6 skin are protected better than everyone else against sunburn, they are particularly prone to vitamin D deficiency bone problems, particularly if they live in locations and situations that deprive them of sunlight. Types 3 and 4 skin are the intermediate types. Type 3 skin can tan, but it can burn before the tanning process kicks in, while type 4 tans easily with minimal burning. Types 2 is between types 1 and 3, meaning that it burns very easily but can tan a teeny weeny bit, while type 5 is brown skin that tans very darkly and easily.

For people of intermediate skin types, living in temperate to subtropical regions, it has been calculated that going outside at noon in summer for a few minutes each day with no sunscreen on your face and neck is enough to give you ample amounts of vitamin D. This may sound like a short period of time, but at noon in summer it also can bring you close to the point of burning, so you really need to control it. Adjusting for later hours in the afternoon and earlier hours in the morning, and for other seasons of the year, you increase the amount of time in the Sun. Dividing your Sun time into several shorter bouts of 1 or 2 minutes is an excellent way to reduce the risk of sunburn and skin cancer. On top of this, people of darker skin types need increased time outside, while those with lighter skin need less time.

Now, when it comes to vitamin D concentrations in blood, dietary factors are also at play. In Nordic countries, skin color is typically very light, people get very little direct sunlight, and yet most of these countries showed fairly high blood levels of vitamin D in the recent study. However, their diets include a lot of fish that provide them with vitamin D. Compared with the other Nordic countries, Iceland showed a lower average blood concentration of vitamin D (57 nmol/L), along with an alarmingly high number of cases of COVID-19 per one million people, although the number of Icelandic COVID-19 deaths per one million people was relatively low. Sweden showed a much higher number of deaths per million people than Iceland, which may relate to Sweden’s avoidance of complete social distancing policy of the surrounding countries. Meanwhile, the overall number of Swedish cases per million people was much lower than that of Iceland and Norway too, but the vitamin D levels were highest of all in Sweden (73.5 mmol/L). They must eat a lot of fish. In contrast, the number of COVID-19 deaths per million were horrifyingly high in Italy and Spain while the vitamin D levels were very low (50 mmol/L for Italy and 42 mmol/L for Spain, whose death rate was higher than Italy). Meanwhile, the country of Slovakia showed vitamin D levels as high as 81.5 mmol/L and the lowest COVID-19 death rate (per million people) of all the countries in the study.

Now, if you’re wondering about all of the sunshine in Spain and Italy and trying to rectify that with the high number of COVID-19 cases and deaths, the answer relates to very high numbers of elderly people in those countries and the fact that the elderly people avoid sunlight, especially in the middle of the day.

The results of the study tie in with those of earlier studies relating deficiency of vitamin D to an increased risk for viral infections and studies suggesting that vitamin D helps your white blood cells function in defending the body. Does it mean that vitamin D can prevent COVID-19 or its life-threatening complications? The answer is that we don’t know. As noted earlier, the new study revealed a crude relation between vitamin D concentration in blood and COVID-19; here, we emphasize crude. In the study, the country of Portugal showed the lowest vitamin D levels of all (39 mmol/L), but the number of COVID-19 cases and deaths per million people was outstepped by several other countries. Consequently, the recommendation of the study authors is that studies should now be initiated to address test vitamin D clinically as an anti-COVID-19 measure.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

Leave a Reply