Vitamin D is best known for its role in bone health.
It facilitates calcium absorption from the digestive system, normal calcium and phosphate in blood, and bone mineralization. Vitamin D is also involved with cell differentiation and immune function.
Current research is investigating effects of vitamin D status on blood pressure regulation, immune function, autoimmune disease, some cancers and glucose tolerance. There is evidence of an effect of vitamin D on disease risk and outcome, but the specific actions of vitamin D haven’t been clarified.
Vitamin D can be synthesized in skin exposed to specific rays of sunlight, which are strongest in summer in northern latitudes, or year-round in areas close to the Equator. The recommended intake for vitamin D is presumed to be sufficient for someone with little sun exposure.
RDA for vitamin D is given in International Units, which are a measure of biological activity rather than weight. The recommendation for infants less than 1 year old is an Adequate Intake value.
Recommended Dietary Allowances for Vitamin D
Which Foods Have Vitamin D?
Milk, fortified with vitamin D
Yogurt, made from fortified milk
Ready-to-eat cereals are frequently fortified with vitamin D in varying amounts. Some orange juice and meal bars may also be fortified.
What Happens If You Don’t Get Enough Vitamin D?
The most severe sign of vitamin D deficiency is rickets, which is the failure of bones to grow properly in infants and children. Poor vitamin D status leads to poor calcium status and inadequate bone mineralization.
Affected children can develop permanent bone deformities.
A sign of deficiency in adults is osteomalacia, or thinning bones. Blood calcium levels are maintained by pulling calcium out of bones. Poor vitamin D and calcium status means bones gradually lose calcium over time. Another possible symptom is chronic muscle pain and weakness.