Human beings make their own vitamin D in response to sunlight, which is why vitamin D is often called the "sunshine" vitamin." It is also called that because vitamin D has been linked to mood and seasonal depression.
When humans are not exposed to enough natural sunlight, they become deficient in vitamin D. This is especially true in northern climates that get less sunlight for long periods during the year. In addition, society's fear of skin cancer risk has caused people to avoid exposing themselves to sunlight by using sunscreen and protective clothing. Although these behaviors do protect skin from harmful UV rays, those same rays are required for people to make vitamin D, which has been shown to help prevent other kinds of cancer and chronic diseases.
There are other factors that can cause vitamin D deficiency, including darkly pigmented skin and problems with intestinal absorption of vitamin D. Obese individuals often have lower than normal vitamin D levels, so maintaining a healthy body mass index is critical for avoiding vitamin D deficiency.
Effects of Vitamin D Deficiency
It has been shown that many people, especially in northern latitudes, have insufficient levels of vitamin D. This is especially true in the elderly and people with darkly pigmented skin. These groups of people should supplement with vitamin D or eat more foods containing vitamin D.
Vitamin D is necessary for the proper metabolism of calcium. This is why vitamin D deficiency in children causes Rickets, improper bone formation and calcification. In older adults, vitamin D deficiency accelerates osteoporosis.
A common symptom of vitamin D deficiency is bone pain and muscle weakness. However, it is possible to have vitamin D insufficiency, which is less serious than deficiency, but still has some clinical effects, including mood issues, asthma in children, and an increased risk for both heart disease and cancer.
Vitamin D may also play a role in the prevention and treatment of type 1 and type 2 diabetes, hypertension, glucose intolerance, and multiple sclerosis.
Recent research has suggested that the "Recommended Daily Allowance" of vitamin D (RDA) of 400 IU maybe too low, especially in northern latitudes. Nutrition researchers are now recommending the vitamin D RDA be raised to 2000 IU to prevent vitamin D insufficiency, and that vitamin D intakes as high as 5000 IU are safe without danger of vitamin D toxicity or overdose.
Always discuss your health concerns and nutritional needs with a trained health care practitioner.
Vitamin D Food Sources
Cod liver oil is a rich source of vitamin D. Most marine fish and some shellfish contain significant amounts of vitamin D in their raw form, but cooking can destroy vitamin D in these foods. Therefore, some types of sushi may provide ample vitamin D.
Other than mushrooms, there are few naturally occurring vitamin D foods. Egg yolks contain vitamin D, but again cooking destroys it. However, many foods are fortified with isolated, synthetic vitamin D3, like orange juice, milk (both dairy and soy), and cereal products.
REFERENCES
1. Role of vitamin D in cardiovascular disease. (FREE FULL TEXT)
2. Vitamin D, sunlight exposure, and bone density in elderly African American females of low socioeconomic status. (FREE FULL TEXT)
3. Does vitamin d deficiency cause hypertension? Current evidence from clinical studies and potential mechanisms. (FREE FULL TEXT)
4. Possible Health Implications and Low Vitamin D Status during Childhood and Adolescence: An Updated Mini Review. (FREE FULL TEXT)
5. Role of vitamin d in insulin secretion and insulin sensitivity for glucose homeostasis. (FREE FULL TEXT)
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Great article on a timely topic. I wrote a 6-page newsletter for an alternative health client on this same topic with many of the same points you struck here. One aspect of the problem that stuck with me as the mother of a little girl--apparently most of our bone mass is created prior to puberty. Although we certainly promote milk drinking for calcium/vitamin D, exercise has been shown in some studies to be even more important in building peak bone mass in children. There are societies where kids are deficient in the nutrients but get plenty of sun and exercise and develop healthy bones anyway.
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