Posted on: June 26, 2009
The Dirt on Vitamin D
Determining whether vitamin D is really the solar solution to all life's ills
By Anna Sachse
CTW Features
Actually reduce cancer risk by sunbathing? Move pregnant women to Florida to prevent their children from developing autism? Pop an all-natural depression medication?
Excited reporters and supplement companies are attributing more and more health benefits to the latest "wonder drug" – vitamin D. But most of their assertions are based on epidemiological studies still in their preliminary stages. What are the hard facts on what D can really do, what might it be able to do, how do you get it and how much do you really need? Here's the truth behind the latest health hype.
How It Works
According to the National Institutes of Health's Office of Dietary Supplements, Bethesda, Md., vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others and available as a dietary supplement. It is also produced endogenously when the sun's UVB rays strike the skin, triggering vitamin D synthesis. There are actually two forms that are important in humans: cholecalciferol (vitamin D3) which is the kind that's either synthesized in skin by sunlight or in irradiated lanolin, and ergocalciferol (vitamin D2), which is synthesized by fungi and plants. Food and supplements may be fortified with either form, however, recent research has found D3 to be over three times more effective in humans and many supplement companies that previously used D2 are making the switch.
Regardless of what kind or where it is obtained from (sun exposure, food or supplements), vitamin D is actually biologically inactive until it is modified first by the liver to produce the blood form, 25-hydroxyvitamin D3 or calcidiol, and then in the kidney to become the hormone 1,25-dihydroxyvitamin D3, or calcitriol, that "does all the good things," says Hector F. DeLuca, Ph.D, Steenbock Research Professor in the Department of Biochemistry at the University of Wisconsin-Madison. DeLuca's lab was responsible for discovering this important sequential process in the 1960s.
What Can It Really Do
New claims of what vitamin D can do keep cropping up, but in truth, only a few are definitive at this time. The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus and aid in calcium absorption, helping to form, mineralize and maintain strong bones, explains Mary Frances Picciano, PhD, a Senior Nutrition Research Scientist for ODS. Specifically, adequate D intake prevents rickets (soft bones and skeletal deformities) in children and osteomalacia (weak bones and muscles) in adults. Vitamin D is also often administered to patients who are experiencing kidney failure to prevent dialysis from degrading the bones.
"But it's not just for bones," says DeLuca. "Clear links have established that therapy with vitamin D can treat hyperparathyroidism and suppress psoriasis."
What Might It Be Able to Do
But the positive implications of what D can do for you appear to be far more far-reaching. Current research suggests that vitamin D can be used to combat heart disease, certain types of cancer, autoimmune diseases such as multiple sclerosis, rheumatoid arthritis and diabetes, infectious diseases such as tuberculosis and the flu and maybe even mental illnesses including Seasonal Affective Disorder, schizophrenia and depression.
There are a lot of interesting observational studies focused on D and doctors are enthusiastic, says Picciano. "But they could lead us down the wrong path. We need appropriate controls to see if they hold water. Nothing can take the place of double-blind, randomized tests."
In the meantime, however, doing the D within the safe limits is probably a worthwhile risk.
