Vitamin D is a nutrient essential for calcium balance and bone health, among other uses. Vitamin D is fat-soluble, so it is stored in the liver and fatty tissues to be used as needed. Vitamin D2 is a vitamin found in plants, specifically mushrooms. It has been used to replete low vitamin D and is a good option for those following a vegetarian or vegan diet. Vitamin D3 can be obtained naturally from dietary sources such as egg yolk, cheeses, and oily fish. Vitamin D3 is also mainly synthesized in our skin by UV-B mediated conversion.
Vitamin D is inactive when taken and must move to the liver to form 25-hydroxy vitamin D, which is mainly tested in blood. And then, from the liver, it travels to the kidneys to form the biologically active vitamin that functions as a steroid hormone.
Deficiency is a concern because vitamin D assists with calcium and phosphorus absorption from the intestines and maintains blood levels of calcium and bone mineralization. Vitamin D also modulates immune function and helps with the secretion of insulin. Within the past two years, vitamin D has received more notice as it was a prominent player in the COVID-19 pandemic. With an increase in notoriety, this sunshine vitamin does not come without potential risks.
Vitamin D is a fat-soluble vitamin in the body, along with vitamins A, E, and K. As a result, it undergoes widespread fat tissue storage. Over time with continued dosing, especially with high doses, the vitamin D level can increase to levels that are no longer therapeutic or safe. Due to a broad therapeutic index, too high vitamin D levels are extremely rare; however, a small number of cases show vitamin d toxicity (levels ˃250 nmol/L) and intoxication (levels ˃375 nmol/L ) can occur at excessively high doses of supplementation. And because vitamin D is well stored in the body, symptoms of vitamin D toxicity can last for several weeks. Overdose symptoms may include neuropsychiatric features like drowsiness, confusion, psychosis, depression, and coma. Possible gastrointestinal symptoms may also be seen that include loss of appetite, stomach pain, vomiting, and constipation. Abnormal heartbeats and changes in urination may also be seen.
The current recommended intake of vitamin D is 400 IU per day alongside reasonable sun exposure for all healthy children and adults to prevent vitamin D deficiency. Higher dosages should be discussed and monitored by your health care provider. Breastfed infants of mothers who are not supplementing with appropriate amounts of vitamin D should also receive 400IU per day to prevent deficiency.
Discussing your vitamin D status with your primary care provider will help to assure your levels are sufficient and not too high. If you do supplement with vitamin D, it is best to take it either as an emulsified supplement or capsule that is taken with a meal.
- Nutritional Medicine by Alan Gaby, MD