Vitamin D

Vitamin D: Information

Until fairly recently, vitamin D was regarded as a rather insignificant nutrient, whose benefits pertained almost exclusively to bone health and little else. In the past decade, however, vitamin D (a.k.a. calcitriol) has received an enormous increase in attention as researchers and medical doctors recognize its crucial, complex role in supporting overall health, especially with respect to the immune system.¹

Some of the confusion and prior lack of interest in vitamin D stemmed from the fact that although classified as a fat-soluble vitamin, vitamin D functions as a hormone,² which means it initiates and regulates critical functions in target tissues throughout the body. Also unlike other vitamins, our primary source of vitamin D is not diet; vitamin D is instead synthesized in the skin from cholesterol upon exposure to sunlight. But because vitamin D can also be obtained through supplements and the diet, vitamin D has been regarded as a fat-soluble nutrient like vitamin A, vitamin E and vitamin K. All types of vitamin D - that which is made in the skin, that which comes from animal-source vitamin D supplements (D3 or cholecalciferol), or fungal source-supplements (D2 or ergocalciferol) - each must first be converted into the active form of vitamin D (25-hydroxyvitamin D ) by the liver.

Small amounts of vitamin D precursors are found in cod liver oil, fatty fish, egg yolks and fortified food products. Optimal production of vitamin D can only occur with supplementation or regular and significant exposure of unprotected skin to sunlight of fairly high intensity and for a sufficient duration.³ Since many people cannot receive this kind of regular sun exposure, suboptimal levels and vitamin D deficiencies may be much more common than previously thought, and medical experts have increased the recommended amounts of vitamin D substantially.⁴

Vitamin D: More Important Than Ever

Vitamin D protects health in many ways. In the nucleus of cells, vitamin D regulates the transcription of genetic code so cell growth, function and maintenance are carried out properly and unchecked cell proliferation is controlled; these functions have prompted many studies of vitamin D with respect to cancer.⁵ Vitamin D also helps regulate calcium metabolism by affecting absorption in the intestines, re-absorption from the kidneys and the mobilization of calcium from bone when insufficient amounts of vitamins D are present.⁶ Vitamin D modulates the immune system, enhancing function and inhibiting the development of autoimmune reactions.⁷ Vitamin D is also thought to play a role in insulin metabolism⁸ and regulating blood pressure,⁹ both of which can be adversely affected by insufficient level. Finally, research shows that vitamin D may be beneficial for seasonal affective disorder (SAD).¹⁰

Vitamin D: Deficiency and Supplementation

The ability to synthesize and absorb vitamin D diminishes with age, and is impaired in overweight individuals, putting the obese and elderly populations at a greater risk for deficiency. Strict vegetarians who do not consume fish, eggs or dairy products are also at risk for deficiency. In children, deficiency of vitamin D can cause rickets but this is rarely seen anymore because of vitamin-D fortified foods. In adults, vitamin D levels can be only determined by a doctor. Most health experts agree that vitamin D supplementation is essential for all adults who do not receive regular sun exposure.

Adults usually supplement 400-2000 IU of vitamin D per day, some take more or less on the advice of their doctor.

Using Vitamin D Supplements

Vitamin D supplements come in two forms. Animal-derived vitamin D (D3) is called cholecalciferol while fungal-derived vitamin D (D2) is called ergocalciferol. There is mixed evidence that the D3 form is more potent.¹¹ Pregnant women should not take more than the recommended dose, as high doses of vitamin D may be unhealthy for the developing fetus. Strict vegetarians who do not consume animal products should consider a vitamin D supplement.

Side-effects and Cautions:

Consult your physician before using any dietary supplements if you are currently taking any medications.Use as directed.

References:
1. Curr Opin Investig Drugs. 2008 May;9(5):485-90.
2. Clin J Am Soc Nephrol. 2008 Jun 4.
3. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S.
4. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S.
5. Ann Epidemiol. 2008 May 24
6. Linus Pauling Institute Micronutrient Information Center
7. Scand J Immunol. 2008 May 29.
8. Diabetes Obes Metab. 2008 Mar;10(3):185-97.
9. Nutr Rev. 2008 May;66(5):291-7.
10. J Nutr Health Aging. 1999;3(1):5-7.
11. J Clin Endocrinol Metab. 2008 Mar;93(3):677-81. Epub 2007 Dec 18.