Anyone who watches television, stares at a computer screen or listens to a radio already knows the news: Vitamin D not only helps to build strong bones; it probably helps to protect us from heart attacks, cancer, diabetes, and even multiple sclerosis. Alas, many Americans aren’t getting enough of the “sunshine vitamin.”
Vitamin D Overdoses from Fortified Foods Led to Excessive Caution
Vitamin D’s role in preventing rickets (a disease characterized by softened and malformed bones) has long been understood. Misguided attempts to prevent rickets in the 1940s by supplementing foodstuffs with vitamin D led to the overdosing of many children, some of whom subsequently suffered irreversible brain damage.
Paradoxically, the ensuing apprehension about vitamin D toxicity resulted in a recommended dietary allowance (RDA) that is too low for most people. Indeed, one study published in the June 2008 issue of Archives of Pediatrics and Adolescent Medicine showed that 40% of American babies and toddlers may have inadequate blood levels of vitamin D; another study suggests that adolescents can and should be taking as much as four times the latest RDA of 600 IU daily.
Vitamin D Is a Hormone Derived from Sun Exposure
Vitamin D is unique among the many vitamins that contribute to human health. It is the only vitamin that the human body, in a self-regulated process, can produce on its own via exposure to sunlight.
About an hour of sun exposure each week is considered sufficient (and this can be achieved in several, short-term forays into the outdoors) but individual needs vary, depending upon age, skin color, and underlying health problems. However, with the well-documented connection between skin cancer and exposure to ultraviolet light, a lot of people are hesitant to spend much time in the sun; they prefer to take a vitamin D supplement instead. In many cases, these individuals will simply take the form of vitamin D that is recommended by their physicians.
Vitamin D3 Is More Effective than D2 for Raising Blood Levels of 25-hydroxyvitamin D
Unfortunately, despite some well-designed studies revealing the superiority of vitamin D3 (cholecalciferol) as a supplement, the form of vitamin D found in most prescription preparations in the US is vitamin D2 (ergocalciferol). It is noteworthy that vitamin D2 was developed and patented by the pharmaceutical industry and has since been prescribed by physicians for patients who need vitamin D. Many doctors don’t know that vitamin D2 differs radically from vitamin D3 in its physiologic activity. Once in the human body, vitamin D2 is inactivated in the normal metabolic pathway that converts vitamin D3 to an active precursor form of the vitamin. Vitamin D3 is the form that leads to higher levels of serum 25-hydroxyvitamin D, which is converted to 1,25-dihydroxyvitamin D, the molecule that confers vitamin D’s benefits. Conversely, the metabolic products of D2 are not efficiently bound to important carrier proteins in the bloodstream, and they don’t effectively activate the appropriate cellular receptors. Finally, vitamin D2 has a shorter shelf life than D3.
In summary, then, it is clear that vitamin D3 is the preferred form of supplemental vitamin D; vitamin D2—in spite of longstanding medical dogma—is simply a less effective form of supplementation.
Sources
- Gordon CM, et al. Prevalence of Vitamin D Deficiency Among Healthy Infants and Toddlers. Arch Pediatr Adol Med. 2008;162(6):505-512
- Vieth R. Critique of the Considerations for Establishing the Tolerable Upper Intake Level for Vitamin D: Critical Need for Revision Upwards. J Nutr. 2006;136(4):1117-1122
- Office of Dietary Supplements: Vitamin D
Stephen Allen Christensen - Dr. Steve Christensen's writing has appeared in magazines, professional journals, poetry anthologies, and children's books since 1976.
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