Vitamin D is responsible for promoting calcium absorption, improving muscle strength and immune function, reducing inflammation and maintaining sufficient blood levels of phosphorus and calcium to support bone formation, mineralization, growth and repair. According to the Mayo Clinic, vitamin D may also provide protection against osteoporosis, high blood pressure, cancer and other autoimmune disease.
Sunlight
Vitamin D is known as the "sunshine vitamin" since sunlight is the richest source. According to Medline Plus, just 10 to 15 minutes of sun exposure three times a week, is enough for the body to produce adequate vitamin D. However, the rays that cause the body to synthesize vitamin D are ultraviolet B (UVB) rays. The Harvard Public School of Health states these rays are stronger near the equator and weaker at higher latitudes such as in Europe and the northern United States.
Risks
While sun exposure is the richest source of vitamin D, it may also be the most dangerous. Excessive exposure to UV radiation is carcinogenic and is responsible for an estimated 1.5 million skin cancers and 8,000 deaths from metastatic melanoma that occur annually in the United States. A safe, yet beneficial, level of sun exposure has not been established.
Other Sources
Vitamin D can also be obtained from diet however, vitamin D does not occur naturally in many foods. Vitamin D is found in fatty fish such as tuna, salmon and mackerel, beef liver, cheese, and egg yolks. Mushrooms also have small amounts of vitamin D, but new ultraviolet exposed mushrooms are being sold with enhanced vitamin D content. According to the Office of Dietary Supplements, the majority of vitamin D provided in the American diet comes from fortified foods such as milk, cereal flours, juices and ice cream.
Supplements are often used by those who are unable to obtain adequate amounts of vitamin D from the sun or diet. Two forms of vitamin D are available in supplement form, D2 and D3. According to the Office of Dietary Supplements, vitamin D3 could be more than three times more effective in raising serum concentrations and maintaining levels for a longer period of time than the D2 version.
Dosing
The United States Institute of Medicine of the National Academy of Sciences has established an adequate intake level of 5 micrograms, or 200 international units (IU), per day. However, these levels are under scrutiny and are being reevaluated.
Deficiency
Low levels of vitamin D may increase the risk of several chronic diseases such as osteoporosis, heart disease, multiple sclerosis and infectious diseases such as tuberculosis and the flu. Certain populations who may be at risk for vitamin D deficiency include individuals who reside in Europe or the norther United States, are overweight, older, have dark skin or who cover up in the sun.
Overdose
Risk of vitamin D overdose from sun exposure or diet is highly unlikely. Supplements however, do have the ability to cause toxicity if taken in excess. If too much vitamin D is in the body, the intestines may absorb too much calcium, causing high levels in the blood. Large amounts of calcium in the blood can lead to calcium deposits in the soft tissues of the body such as the heart and lungs, thereby reducing their functioning capabilities. Other consequences of overdose include kidney stones, vomiting and muscle weakness.
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