Vitamin D Health Benefits
Vitamin D has received quite a bit of attention in the past few years, and with good reason. Several research studies show that many Americans are deficient in vitamin D or have insufficient levels of this vitamin for good health.
Vitamin D is a fat-soluble vitamin that is converted into a hormone in the body. And once converted to its active form, vitamin D plays several important roles in our health. It helps promote the absorption of calcium and maintain blood levels of both calcium and phosphorus – both of these minerals are pulled from the blood to maintain bone health. Vitamin D also plays a role in the immune system functioning, influences gene expression, helps reduce inflammation and alters cell growth and proliferation.
The most well documented health consequences of vitamin D deficiency are the bone diseases rickets in children and osteomalacia in adults. Both diseases are characterized by softening of the bones and skeletal deformities. In addition, vitamin D deficiency has also been associated with musculoskeletal pain and depression.
According to data from the largest nationwide survey on food and nutrient intake, the National Health and Nutrition Examination Survey (NHANES), more than 90% of people in the United States with darker skin (Blacks, Hispanics, and Asians) and almost three fourths of Caucasians suffer from vitamin D insufficiency (defined as a blood vitamin D level of <30 ng/ml).
The following groups of people have the highest risk of developing vitamin D deficiency or insufficiency:
- Infants who are exclusively breastfed.
- Dark skinned individuals. The pigment that makes skin dark, melanin, also protects skin from absorbing sunlight.
- Older individuals. As we age, our body’s ability to make vitamin D and convert it into its active form decreases.
- People exposed to limited sunlight
- People with fat malabsorption. As a fat soluble vitamin, vitamin D requires some dietary fat for proper absorption. Certain diseases increase one’s risk of fat malabsorption including Crohn’s disease, cystic fibrosis, celiac disease, surgical removal of part of the stomach or intestines, and some forms of liver disease.
Sources of Vitamin D
We can obtain vitamin D from our diet; dietary supplements and our body can produce it when our skin is exposed to UVB rays from the sun. However, several factors decrease your body’s ability to manufacture vitamin D upon exposure to sunlight. These include: sunscreen, cloud cover, smog, advanced age and the color of your skin (darker skin absorbs less sunlight). And, because UV radiation is largely responsible for the skin damage and wrinkling that many people associate with aging, many scientists do not recommend increasing your sun exposure in an effort to manufacture more vitamin D.
Vitamin D is found naturally in very few foods though it has been added to various fortified foods such as fortified milk, nutrition bars and some cereals. Foods rich in vitamin D include cooked salmon and mackerel, canned tuna and sardines, fortified milk and cereal.
If you think you may be falling short on your vitamin D intake, get tested and talk to your personal physician about supplementation. Vitamin D supplements offer an easy and practical solution for obtaining vitamin D. There are two types of vitamin D found in supplements, vitamin D2 (ergocalciferol) and D3 (cholecalciferol). However, vitamin D3, may be more effective. And, never consume more vitamin D than recommended by your physician. At very high doses, vitamin D toxicity can occur. Symptoms include: nausea, vomiting, decreased appetite, constipation, weakness and weight loss.
1 Adams, J.S. and M. Hewison. (2010). Update on vitamin D. Journal of Endocrinology and Metabolism, 95, 471-78.
2 Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1997.
3 Holick, M.F. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. (2004). American Journal of Clinical Nutrition, 79, 362-371.
4 Vitamin D Fact Sheet. Office of Dietary Supplements, NIH. http://ods.od.nih.gov/factsheets/vitamind Accessed February 28, 2011.
5 Thacher TD, Clarke BL. Vitamin D insufficiency. Mayo Clin Proc 2011;86(1): 50-60.
6 Plotnikoff GA, Quigley JM. Prevalence of severe hypovitaminosis D in patients with persistant, nonspecific musculoskeletal pain. Mayo Clin Proc 2003;78: 1463-1470.
7 Houghton, L.A. and Vieth, R. (2006). The case against ergocalciferol (vitamin D2) as a vitamin supplement. American Journal of Clinical Nutrition, 84, 694-7.