^{Vitamin D3  is believed to exhibit the most potent} 

^{cancer-inhibiting properties and is the preferred form of the vitamin.}

Those who do follow the suggestion to consume more vitamin D may want to watch for toxicity symptoms of headache, nausea, dizziness, vomiting, loss of appetite and dry mouth--though these are not usually seen outside of underlying health conditions such as kidney or parathyroid hormone dysfunction.

Vitamin D is not prevalent in foods. A study conducted at the Bone Research Laboratory at Boston University School of Medicine revealed that fortified milk may not be a reliable source of vitamin D. Only 29 percent of commercial milk samples tested were within 80­120 percent of the amount stated on the label. Most milk products were over fortified, and a few milk cartons contained no vitamin D at all.¹³ Vitamin D milk fortification procedures vary widely from dairy to dairy. Some dairies place their vitamin D preparations in refrigerated storage, and others do not, which may affect the vitamin D content of the final product.¹⁴

Few vitamins can provide such an array of health benefits as vitamin D. Sunshine is still the most economical and beneficial way to improve circulating vitamin D levels. In addition, the lack of sunlight exposure could lead to more than thinning bones and an increased risk for cancer--there is the added benefit of controlling cholesterol. Since vitamin D is produced naturally within the body, technically it is a hormone. Vitamin D precursors require cholesterol for conversion into the hormone-vitamin. Without adequate sun exposure, vitamin D precursors turn to cholesterol instead of the vitamin. The increased concentration of blood cholesterol during winter months and the fact that outdoor activity (gardening) is associated with lower circulating cholesterol levels in the summer, but not in winter, may explain geographical differences in coronary heart disease incidence.¹⁵

Sunning before 10 a.m. and after 3 p.m. avoids the sun's harshest UV radiation. People who live in areas of winter cloud cover, are homebound, or don't get enough sun should consider naturally compounded vitamin D3 (cholecalciferol) supplements.

Bill Sardi is a health journalist and consumer advocate in Diamond Bar, Calif. His recent publications include The Iron Time Bomb (Purity Pub., 1999) and All About Eyes Naturally (Avery Publishing Group, 2000).