Vitamin D has been called the “sunshine vitamin” because it is activated by ultraviolet light striking our skin. It is necessary for proper absorption of calcium from our diet and for healthy bone metabolism. Low vitamin D levels are common here in the northwest because of our cool cloudy climate, and because we all cover up with clothing most of the year. This increases one’s risk of osteoporosis later in life (in both men and women). There have been other associations noted in people with low vitamin D levels. These are not yet proven, but the circumstantial evidence is strong: They include an increased risk of multiple sclerosis, colon cancer, breast cancer, prostate cancer, lupus, cardiovascular disease, and depression. Vitamin D also activates a protein known to help fight tuberculosis infection. (Probably why many of those “consumption” patients who moved to Arizona for the warm dry air often got better. Doc Holliday didn’t, but he spent much of his time in the saloons.)
Normal vitamin D levels in the blood run 30-100 ng/mL. Toxicity is seen with levels above 150 ng/mL, and because vitamin D is fat-soluble, taking too much can over time result in accumulation causing skin, mucosal, and liver abnormalities. There are two kinds of vitamin D supplements, ergocalciferol (vitamin D2) and calcitriol (vitamin D3). We recommend taking the more metabolically active vitamin D3 in a dose of 2000 IU (international units) daily. Most multivitamins contain 400 – 600 IU, and if one drinks milk regularly it is possible to get 300+ IU from that fortified dairy product. A fifteen minute whole body exposure to full sunlight can generate 20,000 IU or more, and lifeguards in the summertime routinely run blood levels of 100 ng/mL. We do not endorse prolonged sun exposure (tanning) because of the associated increased risk of skin cancer occurring later in life. The most dangerous of these is melanoma, which has been increasing in frequency amongst the general population in recent years.
