Vitamin D, also known as the "sunshine vitamin," is a fat-soluble vitamin essential for good health. It has many important functions including calcium absorption, maintaining blood calcium levels, bone growth and immune system function. Without adequate amounts of vitamin D, the body cannot use calcium effectively, and bones may become weak. A vitamin D deficiency can cause osteoporosis in adults and rickets in children.
Sunlight
Humans can synthesize vitamin D when their skin is exposed to UVB radiation from natural sunlight. Exposure to UVB wavelengths between 290 and 315 nanometers enables most people to manufacture enough vitamin D for good health. Spending just five to 10 minutes outdoors in the sunshine, two to three times weekly, helps prevent vitamin D deficiency in light-skinned people, notes the Linus Pauling Institute. Dark-skinned people are likely to synthesize less vitamin D in their skin than people with light skin because they do not absorb sunlight as efficiently.
Fish
Vitamin D rarely occurs naturally in foods. The best natural sources of vitamin D include fatty fish such as salmon, sardines, mackerel, tuna and herring as well as fish oils. A 3-oz. serving of canned pink salmon provides 13.3 mcg of vitamin D, 3 oz. of canned sardines contains 5.8 mcg and a 3-oz. tin of mackerel provides 5.3 mcg of vitamin D, according to the Linus Pauling Institute.
Fortified Foods
Some foods such as milk, cereals, breads, margarine and orange juice are fortified with vitamin D to help people meet their vitamin D requirements. An 8-oz. serving of fortified cow's milk provides 2.5 mcg of vitamin D, 8 oz. of fortified orange juice contains 2.5 mcg and 1 cup of fortified breakfast cereal provides 1.3 mcg of vitamin D. Infant formula contains 10 mcg of vitamin D per quart, says the Linus Pauling Institute. Vitamin D is also found in eggs laid by hens fed vitamin D.
Supplements
People who have little sunlight exposure such as seniors and those living in northern areas may need to take supplements to meet their vitamin D requirements. A vitamin D deficiency increases the risk of falling, so supplementation may help seniors, notes the University of Maryland Medical Center. Over-the-counter vitamin D supplements usually contain 10 mcg of vitamin D.
Requirements
The recommended dietary allowance for vitamin D for adults is 15 mcg. Adults aged 70 years and over require 20 mcg of vitamin D per day. The adequate intake for vitamin D for infants under 12 months is 10 mcg. Breastfed infants require 10 mcg of vitamin D supplementation daily until they are weaned and drinking fortified milk, according to the Office of Dietary Supplements.
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