As a holistic psychiatrist, I am quite familiar with vitamin D deficiency. I check a vitamin D blood level on every single patient as part of their initial evaluation as there is evidence that low vitamin levels are linked to depression. In my experience, around 90% of patients have some level of vitamin D deficiency, and at least 50% of them are severely deficient. You can obtain Vitamin D from your diet, as well as from sunlight (when your skin is exposed to sunlight, it makes vitamin D from cholesterol). However, studies have shown that most individuals do not consume enough vitamin D, and vitamin D deficiency is a worldwide problem. Vitamin D deficiency has now been linked to breast cancer, colon cancer, prostate cancer, heart disease, weight gain, and other issues.
In addition, vitamin D acts as an immune system modulator, reducing inflammatory cytokines and increasing the “oxidative burst” potential of macrophages. It also stimulates molecules inside of neutrophils, monocytes, natural killer cells, and in the lining of the lung, where they help fight infections.
In 2017, the BMJ released a systematic review and meta-analysis using data from 25 randomized controlled trials. Researchers evaluated the incidence of acute respiratory infection and found that vitamin D supplementation is safe and that it protects against acute respiratory tract infection.
Now, a review article recently published provides evidence that Vitamin D supplementation could reduce risk of influenza and COVID-19 infections and death and recommends that people at risk of influenza and/or COVID-19 consider taking supplemental vitamin D.
I believe this is a wise recommendation, with a fairly high potential benefit and low risk. Normally, I would recommend obtaining a blood level before starting supplementation, but given that this is not an option currently for most people, it is generally safe to start taking 5,000 IU of vitamin D daily and then have your levels checked when possible (but you should always discuss this with your healthcare provider).
While increasing your vitamin D level is likely a helpful way to defend your body against influenza and COVID-10 infection, please remember that the MOST effective ways continue to be social distancing and hand washing! In addition, eating a healthy diet with plenty of fresh fruits and vegetables, getting your daily exercise and sleeping at least 7 hours every night are the best ways to support your immune system health!