Vitamin D

Salmon CevicheVitamin 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

Vitamin DSource: Office of Dietary Supplements, National Institutes of Health

Which Foods Have Vitamin D?

Cod liver oil
Salmon
Swordfish
Trout
Halibut
Milk, fortified with vitamin D
Soy and alternative milk, if fortified with vitamin D
Yogurt, made from fortified milk
Beef liver
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.

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