Vitamin D is a fat-soluble nutrient. It is one of the 24 micronutrients critical for human survival. The sun is the major natural source through eliciting vitamin D production in the skin, but vitamin D is also found naturally in oily fish and eggs and is added to milk and milk alternatives.
Supplemental vitamin D is associated with a range of benefits, including improved immune health, bone health, and well-being. Supplementation may also reduce the risk of cancer mortality, diabetes, and multiple sclerosis.
The effects of vitamin D likely depend on a person’s circulating levels of 25-hydroxyvitamin D (25(OH)D; a form of vitamin D that is measured in blood samples to determine vitamin D status), and many of its benefits will only be seen when a deficiency is reversed.
Extremely high doses of vitamin D can lead to vitamin D toxicity, which causes hypercalcemia (excess calcium in the blood) and can result in a wide variety of health problems. Vitamin D supplementation may also have risks independent of vitamin D toxicity. A few trials on older adults have found that vitamin D increased the risk of falling, and one study observed a decrease in bone mineral density among women taking high doses of vitamin D.
- Cholecalciferol (Vitamin D3)
- Ergocalciferol (Vitamin D2)
- Calcitriol or 1
- 25-Dihydroxyvitamin D (Hormonally active yet not directly supplemented form)
The recommended daily allowance for Vitamin D is currently set at 400–800 IU/day, but this may be too low for many adults. For moderate supplementation, a 1,000–2,000 IU dose of vitamin D3 is sufficient to meet the needs of most of the population. Higher daily doses are in the range of 20–80 IU per kilogram of body weight.
The Upper Tolerable Intake Level in the United States and Canada is 4,000 IU per day (IU/day). It’s been suggested that the true Upper Tolerable Intake Level may actually be as high as 10,000 IU/day, but there are limited data on health outcomes using doses near this amount.
Vitamin D3 supplementation (cholecalciferol) is recommended over D2 supplementation (ergocalciferol) because D3 tends to raise blood levels more effectively.
Vitamin D should be taken daily, with meals or a source of fat.