Vitamin D deficiency is surprisingly common. Age, race, season, and latitude are important is disease prevalence.
Studies in the elderly and in nursing home residents report a prevalence which ranges from 25% to 54%. A recent survey of medical in patients in Boston reported a prevalence of vitamin D deficiency of 57%. Among hospitalized patients under 65 years of age, the prevalence of Vitamin D deficiency was 42%.
The prevalence of vitamin D deficiency in internal medicine residents (doctors intraining) increased from 25% in the fall, to 50% in the spring and winter.
Studies have shown that vitamin D and calcium supplementation increase bone mineral density and reduce fracture rates in elderly patients. A study reported in the British Medical Journal in 1994 looked at 1400 elderly patients. These were all ambulatory women. Women treated with 800 International Units (IU) of vitamin D and 1200 mgs of calcium per day had 23% fewer hip fractures compared to women treated with placebo.
Five to ten minutes of exposure to sunlight on the face, hands, and arms, two to three days a week is required to synthesize sufficient amounts of vitamin D. Few natural foods contain vitamin D. The major dietary source of vitamin D is fortified foods which include milk, cereal, margarine, and some brands of orange juice and yogurt.
Unfortunately, fortified foods do not always contain the amount of vitamin D listed on the label. Studies have found that up to 70% of milk samples do not contain the 400 IU per quart noted on the label.
Although there are many risk factors for vitamin D deficiency, the two most common are decreased skin synthesis, which declines with age, and inadequate dietary or supplemental intake. Decreased absorption is another common cause of vitamin D deficiency.
Treatment requires high doses of vitamin D until total body stores have been replenished. Patients with mild to moderate deficiency can be replenished with 50,000 IU of vitamin D once a week for six to eight weeks. Severely deficient patients (who have less than 8 ng/ml) may require 50,000 units twice a week.
Once vitamin D levels have been replenished the patient can switch to maintenance therapy which is typically 1,000 IU per day.
Toxic effects are uncommon, and are typically seen only in patients taking high daily doses (more than 40,000IU) for weeks to months with serum vitamin D levels of more than 100 ng/ml. Too much calcium in the urine is typically the first toxicity. This often manifests itself as kidney stones.
