VITAMIN D

What is vitamin D?

Vitamin D can be found in foods, and our bodies can make it from sunlight. It is a fat-soluble vitamin [^[1]]. Globally, over 1 billion people have a vitamin D deficiency, which is why the vitamin is often added to fortified foods such as cereals [^[2]].

What does vitamin D do in the body?

Vitamin D is important in bone health due to its role in calcium metabolism. Relevant to Long COVID, Vitamin D’s role in immune function is well-established. It plays a role not only in innate and acquired immunity but also in the immune response to viruses [^[3]]. Vitamin D is linked to a lower risk of unchecked inflammation and cytokine storm in older patients with COVID-19 [^[4]].

How can vitamin D help alleviate certain Long COVID symptoms and pathophysiology?

Vitamin D has multiple effects on biochemical pathways involved in Long COVID. It reduces inflammation, and in people with a vitamin D deficiency, supplementation can reduce fatigue [^[4]]. However, a study of Long COVID patients did not find a link between persistent fatigue, exercise tolerance, and vitamin D levels [^[5]].

In patients with COVID-19, vitamin D deficiency is also related to the severity of the disease, including respiratory failure and mortality. A study of Long COVID patients and vitamin D found that vitamin D deficiency is associated with delayed recovery [^[6]]. The study also found that a combination of zinc and vitamin D deficiency, but not a zinc deficiency without a vitamin D deficiency, was associated with Long COVID in patients under 65. However, older people with Long COVID also stand to benefit from the health benefits of proper vitamin D supplementation.