The Health Diva

Insufficient sun exposure

By far the most important D-deficiency contributing factor faced worldwide is insufficient exposure to sunlight. More specifically, it is ultraviolet B sunlight in the range of 290-300nm that is needed to convert 7-dehydrocholesterol found in our skin cells into cholecalciferol (the preliminary form of vitamin D3).

Although the task of “getting enough sunlight” may seem like a fairly straightforward one, the relationship between our vitamin D status and our time in the sun is not nearly as simple as many people might think. First, there is the fluctuating nature of UVB light. UVB light-the kind needed for skin synthesis of vitamin D-is not always present with the same intensity just because there is visible sunlight. The intensity of UVB light varies dramatically with geographical location (latitude), time of year, time of day, degree of cloud cover, and other factors. In those countries, being outside on a “bright and sunny day” would not be enough to guarantee adequate skin synthesis of vitamin D. Skin pigmentation also plays an important role in skin synthesis of vitamin D. Darker skin pigmentation means less vitamin D synthesis per minute exposure to UVB light. (In the United States, for example, it is estimated that African American adults are 2-3 times more likely to have vitamin D insufficiency than Caucasian adults.)

Insufficient dietary fat or inability to absorb dietary fat

Since vitamin D is a fat-soluble vitamin, a diet that is extremely low in fat and/or the presence of certain medical conditions that cause a reduction in the ability to absorb dietary fat may cause vitamin D deficiency. These medical conditions include pancreatic enzyme deficiency, Crohn’s disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease. Symptoms of fat malabsorption include diarrhea and greasy stools.

Statin drugs may reduce vitamin D levels.

Many in the medical profession are beginning to recognize that people who take cholesterol-lowering statin drugs are becoming vitamin D-deficient. Cholesterol is required by the body to synthesize vitamin D and statin drugs are are responsible for eliminating it, leading many to speculate that statin drug users do not have enough cholesterol to process vitamin D.

Health conditions that involve the parathyroid gland or kidney

Under certain circumstances, the conversion of inactive forms of vitamin D to calcitriol is impaired. For example, diseases that affect the parathyroid gland, liver, and/or kidney impair the synthesis of the active form of vitamin D.

Breastfeeding and pregnancy

Since nursing mothers must help supply their infants with vitamin D, breastfeeding can pose a challenge both to mothers and infants in terms of vitamin D status. The American Academy of Pediatrics (AAP) and the Canadian Pediatric Society (CPS) have both recommended vitamin D supplementation for both mothers and infants for this reason.

Aging

The production of vitamin D precursors in the skin decreases with age. Additionally, with age the kidneys and many other organ systems and cell types are less able to convert vitamin D to its active hormone form.