Vitamin D AND the Immune System  

COVID-19 is increasingly on people’s minds and many are focusing on how to keep their immune systems strong. There is a link between vitamin D and strong immune systems. Vitamin D can regulate the innate and adaptive immune responses. When vitamin D is deficient there is a link to autoimmune disease and an increased susceptibility to infection.  Cod liver oil, which has a high content of vitamin D, is often used in tuberculosis treatment. A report that included almost 19,000 patients from the years of 1988 to 1994, showed patients reporting low levels of vitamin D (<30 ng/ml) also self-reported recent upper respiratory infections. Although recent studies have not shown consistent results, most likely due to methodological concerns, there is one well-designed study in school aged children that demonstrated that vitamin D administration decreased the flu (influenza) by 42%.

 What is vitamin D and what role does it play?

Vitamin D is a fat soluble vitamin that helps support healthy bones through calcium absorption, promoting bone mineralization, and providing immune and cardiovascular support. It also plays a role in muscle function and the brain function and emotional health.

Which vitamin D supplement is best? How much vitamin D?

There are two major types of vitamin D, vitamin D3 and vitamin D2. Humans produce vitamin D3, also known as cholecalciferol, in their skin when exposed to sunlight. The only other source of vitamin D3 is found in animals. Vitamin D2 is sourced from plant foods and is known as ergocalciferol.

Calcidol, also known as 25-hydroxyvitamin D3, is a pre-hormone made directly from cholecalciferol (vitamin D3). This occurs in the liver by the enzyme 25-hydroxylase CYP27A1. This pre-hormone is not active; however, it is the major form of vitamin D that circulates in the bloodstream. Vitamin D blood tests typically measure the concentration of this pre-hormone. The activated form is known as calcitriol (1,25-dihydroxyvitamin D3). The enzyme 1-alpha-hydroxlation CYP27B1, converts the pre-hormone (calcidiol) in the kidneys to the active form, calcitriol. This is the most potent steroid hormone in the body. (Yes Vitamin D is a hormone, and technically calling it a vitamin is a misnomer).

Most studies show that vitamin D3 (cholecalciferol) is more effective than vitamin D2 (ergocalciferol) at raising blood levels of calcifedol.  The recommended daily dose is 2,000 IU of vitamin D3 per day. Always check with your provider before supplementing.

What about when we age, what happens to our vitamin D?

Studies have found as people age; they lose the amount of vitamin D they are able to produce from the sun. This may be a result of the loss of enzymes needed to synthesize the vitamin. Research has found that low levels of vitamin D may be linked to poor cognitive performances in seniors. In addition, if a person receives an adequate amount of vitamin D it may significantly lower levels of inflammation and physiologic stress, factors that may slow down aging.   

What do my lab levels mean and what is normal?

Typically blood tests measure the levels of the inactive pre-hormone, Calcidol (25-hydroxyvitamin D3). Although this hormone is not active it is the most reliable measurement of an individual’s vitamin D level. Lab level numbers will vary from lab to lab and providers may differ in what they believe is normal or low.  However, most experts recommend having a level between 20 ng/ml to 40 ng/ml, and many will also push for levels between 30 ng/ml to 40 ng/ml. In general levels below 10 ng/ml are considered deficient. If you have your lab levels drawn for vitamin D you will want to work closely with your provider to determine if your levels are low.

References: 

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3166406/. Accessed on March 20, 2020
2. Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010; 91(5):1255–60. [PubMed: 20219962] Accessed on March 20, 2020