Evidence continues to mount regarding the connection between those with COVID-19 whose vitamin D levels are sufficient, and in those whose levels are deficient.

The latest study, published a few days ago, detailed the results gathered from 235 hospitalized COVID-19 patients. These results showed a link between people with sufficient vitamin D levels and survival. Of those patients older than 40 years who had sufficient levels, nearly 10% died, as opposed to the 20% with poorer levels, who did perish. Of the 235 patients, 74% had severe infection; of these, 32.8% had sufficient vitamin D levels.

Another important finding involved a biomarker for inflammation, known as C-reactive protein. Inflammation occurs when the body is under siege, from a virus, bacteria, and so on. It is the body's way of protecting tissue. C-reaction protein rises in the presence of inflammation.

But too much of this protein, released from the liver, can cause a cytokine storm. The immune system releases cytokines to fight foreign invaders, but a storm can cause the immune system to get out of control.

Patients with enough vitamin D found in their blood also had reduced levels of c-reactive protein.

The upshot, said the authors, is for people to maintain their vitamin D levels: with enough vitamin D, a patient who contracts COVID-19 has a better chance of fending off severe illness and death.

Other published studies indicate that vitamin D may also reduce the risk of catching COVID-19.

Two recent studies found that people who had subnormal vitamin D levels contracted COVID-19 more often than people with recommended levels. The first study, published in May in the Irish Medical Journal, searched through the literature for records of older patients in Europe to look for a connection between vitamin D levels and the coronavirus infection.

The researchers expected that people in the sunnier countries, like Italy and Spain, would have higher levels than the more northern countries, like Norway, Finland and Sweden. They found, however, that the opposite was true. Citizens of the northern countries, where foods are fortified with vitamin D and supplements are more common had higher levels of the vitamin in their blood. They also had the lowest rates of COVID-19 infection and death. However, the authors also wrote that there are many issues that weren’t investigated, such as how each country measures vitamin D levels, and other possible reasons why their citizens may be more infected than others – including how quickly the infection spread.

Another article, this one published in JAMA Network Open in August, was based on a US study of almost 500 patients. The researchers looked at patients who had had their vitamin D blood levels measured within a year of being tested for COVID-19. The results showed that patients who were vitamin D deficient were almost twice as likely to contract COVID-19 than patients with normal levels.

The US-based researchers did note that there are many reasons why someone might be vitamin-D deficient, including chronic health issues or lifestyle factors that limit their exposure to the vitamin. These, too, could have an impact on contracting the virus. They encouraged further studies to look into the issue.

But these studies run contrary to what researchers from the University of Glasgow found, however. Their study, published in the July/August issue of Diabetes & Metabolic Syndrome, looked at almost 1,500 people in the United Kingdom who had tested positive for COVID-19 and whose vitamin D levels were measured between 2006 and 2010. The researchers did not find that vitamin D levels influenced risk of infection.

Should you increase your vitamin D exposure or consumption?

Since vitamin D is a vital part of staying healthy, it’s not a bad idea to ask your physician for a blood test to measure how much of the vitamin you have in your blood. Then, if you don’t have enough, you can adjust your diet or lifestyle accordingly.

Most healthy people can get enough vitamin D from the sun – usually 15 to 20 minutes 3 times a week. However, how well you absorb the vitamin depends on a few factors, such as:

  • The color of your skin: People with darker skin need more sun exposure to absorb enough of the vitamin.

  • Your location: The farther north you go, the lower the levels of ultraviolet light, which is what causes your body to make vitamin D.

  • The time of year: The further north you are, the seasons also make a difference as to how much UV light you are exposed to by the sun.

  • The time of day: The sun’s rays are most powerful around the noon hour, between 10 am and 2 to 3 pm.

  • The weather: Cloudy days can reduce the amount of UV rays.

  • Air pollution: This can also prevent adequate exposure to UV rays.

Exposing your skin to the sun can lead to other issues, such as damage that can lead to skin cancer, so if you have concerns about how much sun exposure you should get, speak with your physician.

If you can’t get enough sunshine, you can get vitamin D in certain foods and through supplements. Foods with vitamin D are:

  • Fortified dairy and juice products

  • Fatty fish, such as salmon, tuna and mackerel

  • Beef liver

  • Cheese

  • Eggs yolks

If you choose to take supplements, read the labels to ensure you are getting enough vitamin D. These are the recommended amounts per age:

  • Infants up to 6 months: 400 International Units and no more than 1,000 IUs per day

  • 6 months to 1 year: 400 IU, no more than 1,500 IU

  • 1 year to 3 years: 600 IU, no more than 2,500 IU

  • 4 to 8 years: 600 IU, no more than 3,000 IU

  • 9 to 70 years old, including women who are pregnant or breastfeeding: 600 IU, no more than 4,000 IU

  • 71 years old and older: 800 IU, no more than 4,000 IU

If some is good, a lot is not necessarily better

Sometimes it’s tempting to say, “if some is good, more must be better.” But as most things in life, it is moderation that is key. Taking too much vitamin D over an extended period can cause toxicity. It is rare, and it doesn’t happen from too much sun. Vitamin D toxicity occurs when you take too many supplements. Too much of the vitamin can result in calcium build-up in your body, called hypercalcemia. Symptoms include:

  • Nausea

  • Vomiting

  • Increased thirst

  • Increased urination

  • Constipation

  • Weakness

  • Confusion

  • Muscle pains and aches

  • Bone pain

  • Kidney stones

The Takeaway

If you want to eat a healthier diet, one that includes a healthy amount of vitamin D and other nutrients, then consulting with a dietitian is your best bet. Ask your doctor's office if they have a dietitian on staff or if they can refer you to one. Check with your insurance company to see if your plan covers the cost of such a consultation.

This story was updated on October 2, 2020.