Vitamin D - More Than Bone Health
Low Levels Associated With Diabetes, Heart Disease, Cancer
Oct 5, 2009
Vitamin D is a hormone because it can be made in the body. It can be made in the skin by the effect of sunlight (ultraviolet B). Based on the same structure as steroid hormones, it is technically both a paracrine and autocrine hormone (it affects distant organs and the kidney where it can also be made).
The amount of vitamin D in a human can be measured by its blood level. Low levels of vitamin D can affect
- Diabetes control (Journal Clinical Endocrinology Metabolism 2007 Jun;92(6):2017-29);
- Risk for upper respiratory infection (Archives Internal Medicine 2009 Feb 23;169(4):384-90);
- Blood pressure control (National Review Cardiology. 2009 Oct;6(10):621-30);
- Cardiovascular health (National Review Cardiology. 2009 Oct;6(10):621-30); and
- Probably cancer, e.g., breast (Archives Internal Medicine 2007; 167:1050-9), although a later review found less impressive evidence (Journal Steroid Biochemistry Molecular Biology. 2008 Sep;111(3-5):195-9) and prostate (PLoS Medicine 2007; 4:e103); and, as widely known,
- Bone health.
Evidence Not Overwhelming
While individual studies suggest benefits from higher vitamin D levels, enthusiasm needs some tempering. A recent review was cautious. The Tufts Evidence-based Practice Center (EPC), under contract to the Agency for Healthcare Research and Quality (AHRQ), looked at the world’s science literature about vitamin D, and also calcium. In August, 2009, their report concluded
- The majority of the findings concerning vitamin D, calcium, or a combination of both nutrients on the different health outcomes were inconsistent. Synthesizing a ... relation between intake of either vitamin D, calcium, or both nutrients and health outcomes in this heterogeneous body of literature prove [sic] challenging.” (AHRQ Publication No. 09-E015. Rockville, MD: Agency for Healthcare Research and Quality. August, 2009.)
Skin Production Not Enough
It may have been OK to depend on skin production of vitamin D when humans lived in sunny climates and spent most of the day outdoors, but today, vitamin D must be added from foods or supplements. There is disagreement about the minimum amount adults should take in. Many experts suggest at least 1000 IU a day.
Regardless of the ideal amount, it seems levels of vitamin D are dropping among Americans. The average level dropped 20% over ten years in the most recent analysis (Archives Internal Medicine. 2009 Mar 23;169(6):626-32). The drop has been attributed to another health drive, to reduce skin cancer by reducing sun exposure. Awareness that sun damage causes wrinkles probably also changed behaviors.
Certain groups are at special risk to have low vitamin D levels.
- People with dark skin. The sun effect is slower in dark skin.
- People with intestinal disease. Vitamin D is fat soluble, and malabsorption or other intestinal disease can reduce absorption of vitamin D from foods.
- Breastfed infants. Human milk cannot supply enough vitamin D.
- People over age 50. Their skin is less efficient, and their kidneys (that also can produce vitamin D) are, too.
- Canadians and others with limited sun exposure opportunities.
- Obese. The reasons are not fully understood, but obese individuals tend to have lower blood levels.
(Source: National Institutes of Health Office of Dietary Supplements)
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