"Take enough vitamin D" - from JoAnn Manson, Harvard
Relayed by Prof. Ed Miller
Hello. This is Dr JoAnn Manson, professor of medicine at Harvard Medical School and Brigham and Women's Hospital.
I'd like to talk with you about vitamin D and COVID-19. Is there potentially a protective role?
We've known for a long time that it's important to avoid vitamin D deficiency for bone health, cardiometabolic health, and other purposes. But it may be even more important now than ever. There's emerging and growing evidence that vitamin D status may be relevant to the risk of developing COVID-19 infection and to the severity of the disease.
Vitamin D is important to innate immunity and boosts immune function against viral diseases. We also know that vitamin D has an immune-modulating effect and can lower inflammation, and this may be relevant to the respiratory response during COVID-19 and the cytokine storm that's been demonstrated.
There are laboratory (cell-culture) studies of respiratory cells that document some of these effects of vitamin D. There's also evidence that patients with respiratory infections tend to have lower blood levels of 25-hydroxy-vitamin D.
There's now some evidence from COVID-19 patients as well. In an observational study from three South Asian hospitals, the prevalence of vitamin D deficiency was much higher among those with severe COVID illness compared with those with mild illness. In fact, there was about an eightfold higher risk of having severe illness among those who entered with vitamin D deficiency compared with those who had sufficient vitamin D levels.
There's also evidence from a meta-analysis of randomized clinical trials of vitamin D supplementation looking at acute respiratory tract infections (upper and lower). This was published in the British Medical Journal 2 years ago, showing that vitamin D supplementation was associated with a significant reduction in these respiratory tract infections. Overall, it was only a 12% reduction, but among the participants who had profound vitamin D deficiency at baseline (such as a blood level of 25-hydroxy-vitamin D of less than 10 ng/mL), there was a 70% lower risk of respiratory infection with vitamin D supplementation.
So the evidence is becoming quite compelling. It's important that we encourage our patients to be outdoors and physically active, while maintaining social distancing. This will lead to increased synthesis of vitamin D in the skin, just from the incidental sun exposure.
Diet is also important. Everyone should be reading food labels which list the vitamin D content. Food sources that are higher in vitamin D include fortified dairy products, fortified cereals, fatty fish, and sun-dried mushrooms.
For patients who are unable to be outdoors and also have low dietary intake of vitamin D, it's quite reasonable to consider a vitamin D supplement. The recommended dietary allowance of vitamin D is 600-800 IU/daily, but during this period, a multivitamin or supplement containing 1000-2000 IU/daily of vitamin D would be reasonable.
We are in the process of planning a randomized clinical trial of vitamin D supplementation in moderate to high doses to see whether it has a role in the risk of developing COVID-19 infections and also in reducing the severity of disease and improving clinical outcomes.
In the meantime, it's important to encourage measures that will, on a population-wide basis, reduce the risk for vitamin D deficiency.
Thank you so much for your attention. This is JoAnn Manson. Stay safe.
Dr JoAnn Manson is a professor of medicine at Harvard Medical School; and chief of the Division of Preventive Medicine at Brigham and Women's Hospital, in Boston, Massachusetts.
