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Vitamin D

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What is vitamin D?

The main role of vitamin D is to maintain healthy bones by helping calcium and phosphate absorption from the intestines. Not having enough vitamin D raises risk of bone loss and fractures. Vitamin D is likely beneficial for other parts of the body as well. Studies have suggested an overall decrease in death, cancer, heart disease, blood pressure, respiratory illnesses, depression, chances of having a low-birthweight baby.

Vitamin D helps the immune system stay balanced. The way that vitamin D keeps the immune system healthy is very complex. Too much immune stimulation can result in autoimmune diseases. Insufficient immune system activity can result in frequent infections. A large prospective clinical trial showed in 2017 that vitamin D reduces the odds of developing a respiratory infection by approximately 42% in people with low baseline levels of 25-hydroxyvitamin D (< 25 ng/mL). Recent studies suggest that vitamin D plays a critical role in reducing COVID-19 infection and helping recovery from COVI-19 infection.

How to act on the result on Vitamin D has been the subject of great controversy in the medical field. Blood level of 25-hydroxy-vitamin D is usually measured in nanograms per milliliter. One opinion on the vitamin D deficiency is less than 12.5 ng/mL, which is found in about 6% of Americans. The Institute of Medicine (IOM) estimated that a vitamin D level of 20 ng/mL or higher was adequate for good bone health, and subsequently a level below 20 was considered a vitamin D deficiency. In 2011, the Endocrine Society issued a report urging a much higher minimum blood level of vitamin D. It concluded that “at a minimum, we recommend vitamin D levels of 30 ng/mL, and because of the vagaries of some of the assays, to guarantee sufficiency, we recommend between 40 and 60 ng/mL for both children and adults.”

Excessive supplementation of vitamin D may be harmful. Vitamin D is stored in fat and your fat cells can only store so much vitamin D. The result of high levels of vitamin D is high levels of calcium in blood and potentially hypercalcemia and calcification. Too high levels of vitamin D can be immunosuppressive as well.

What are the causes of vitamin D deficiency?

While anyone can be deficient in vitamin D, people who are older, have darker skin, or do not get enough sunlight are more likely to be deficient in vitamin D. People with certain diseases such as cancer often have vitamin D deficiency.

Intervention tips

The main source of vitamin D is production by your body when the skin is exposed to sun. It is estimated that 1000 -1500 hours of sun exposure in the year are needed by most people to produce the necessary amount of vitamin D. Due to vigilant sun protection and other factors, vitamin D deficiency is very common and on the rise. Vitamin D can also be obtained from other sources including some natural foods such as fatty fish, egg yolks, cheese and beef liver as well as foods fortified with vitamin D such as dairy products, soymilk, and cereals. However, many people, especially older adults, people with darker skin and limited sun exposure and overweight, cannot get enough vitamin D from sun exposure and foods and require vitamin D supplements. While a daily supplement of 1000 IU may be sufficient for most people, much higher dose is necessary for those who are deficient in vitamin D level.

Too much vitamin D (>100 ng/ml) can be harmful, increasing risk for fractures, falls and kidney stones, and can be toxic due to excessive level of calcium. There is some evidence that high levels of vitamin D may be associated with certain cancers and mortality. Testing for blood vitamin D level is the best way to find out how much supplementation is needed for each person. We recommend an optimal vitamin D level between 50-80ng/mL to maximize health and longevity.

Further reading

  1. Emily S. Ruiz, M. (2020). Vitamin D: Finding a balance – Harvard Health Blog. Retrieved 24 November 2020, from
  2. Vitamin D Boosts the Immune System. (2020). Retrieved 24 November 2020, from
  3. New research shows a surprising link between coronavirus and vitamin D. (2020). Retrieved 24 November 2020, from
  4. Vitamin D supplements are immunosuppressive | Microbe Minded. (2020). Retrieved 24 November 2020, from