Vitamin D is a fat-soluble vitamin that promotes bone health. It's also important for normal calcium absorption. Vitamin D deficiency can cause rickets in children and osteomalacia in adults.

Vitamin D is synthesised in the skin and obtained from some foods, such as fatty fish (like trout, salmon, tuna and mackerel) and beef liver, and egg yolks.

Vitamin D Role

Vitamin D helps regulate the amount of calcium and phosphate in the blood, which are needed for strong bones. It also helps control inflammation and has roles in brain health and immune function. Most people get vitamin D from dietary sources or sun exposure. But many people have difficulty getting enough, especially those who live far north of the 37-degree latitude line and spend most or all of their time indoors (such as older adults).

People with certain conditions—such as Crohn’s disease or celiac disease, which prevent the intestines from properly absorbing vitamins—are also at higher risk for vitamin D deficiency. So are people with limited sun exposure and those who take anti-inflammatory medications that interfere with vitamin D absorption.

Government and professional guidelines for recommended vitamin D intakes vary. The Endocrine Society recommends routine supplementation with D3, a form of the vitamin that the body easily absorbs, for all children and teens, pregnant women, and people at high risk of insufficient D intake.

Benefits Explained

As part of its role in calcium absorption, vitamin D promotes bone health. It helps prevent rickets in children and osteomalacia (soft bones) in teens and adults. It also helps prevent fractures by increasing the strength of the bones.

It supports the immune system by helping to fight infections and autoimmune diseases such as rheumatoid arthritis, type 1 diabetes and inflammatory bowel disease. Studies have found that vitamin D may help reduce the risk of cancer, heart disease and hypertension and support brain health.

A large clinical trial involving 25,871 men and women 50 years of age and free of previous cancers who were randomly assigned to take either 2,000 IU/day of vitamin D or placebo for five years found that supplemental vitamin D did not reduce the rate of total, hip or nonvertebral fractures compared with placebo. This finding is consistent with other trials involving vitamin D and fractures and with the findings of many previous reviews and meta-analyses.