A Word About Vitamin D

A Word About Vitamin D

Vitamin D is interesting. It is necessary for normal nerve and muscle contraction and for healthy bones. It acts by promoting calcium absorption. Without adequate vitamin D and calcium, nerves and muscles don’t function properly and the bones thin out. In severe cases, the bone wasting is called rickets. Rickets was widespread 100 years ago and caused terrible pain to those affected, but disappeared from the U.S. once milk was fortified with vitamin D.

Vitamin D can be obtained either through the diet or from sun exposure. Good dietary sources include vitamin D fortified milk, fatty fish (salmon, mackerel, etc) and cod liver oil, and from yeasts and some plants. Supplemental multi-vitamins also have vitamin D. The other source, ultraviolet B light from the sun, causes a chemical reaction in the skin to convert a hormone into vitamin D.

Problems arise when people do not receive enough sun exposure or when they have limited intake or poor absorption of vitamin D. Today there is so much emphasis on avoiding the sun and on the use of sunscreens that block UVB, that many people receive very little vitamin D in this way. Chronically ill people who are homebound and rarely, if ever, go outside are at risk of having low vitamin D levels. It is more common, too, in geographical areas that have more cloud cover or short days.

If one’s diet lacks vitamin D, obviously there can be problems. Breast milk contains very little vitamin D, and so the American Academy of Pediatrics recommends that breastfed infants be supplemented. But some medical conditions are associated with low vitamin D absorption, even if it is present in the diet. These include chronic kidney or liver disease, removal of part of the stomach or having a gastric (stomach) bypass, and malabsorption syndromes. Since vitamin D is absorbed in the small intestine, any disease affecting it (such as Chron’s disease) or surgical removal of portions of the small bowel will reduce the amount of vitamin D absorbed. The use of certain medications like anticonvulsants (Dilantin or phenobarbital) or corticosteroids (prednisone, etc.) can also lead to vitamin D deficiency. People who take these drugs require two to five times the recommended daily amount of vitamin D.

Since a low calcium level interferes with nerve and muscle contraction, the body tries to maintain proper concentrations. With low vitamin D, calcium levels fall, so the parathyroid glands secrete a hormone which dissolves calcium from bones. Excessive bone thinning can then occur (osteopenia, osteoporosis, osteomalacia, or even rickets. The absorption of calcium from the bones may cause chronic bone pain and lower extremity weakness. There can be a diffuse discomfort, and women are often misdiagnosed with fibromyalgia, chronic fatigue, or other similar syndromes.

Physicians are not generally trained to check for vitamin D deficiency. A blood test (25-hydroxyvitamin D) can check body levels. Although levels over 10 nmol per L are considered normal, current recommendations have been adjusted to suggest levels of 30 or higher for optimal function.

If there is adequate exposure to sunlight, the current (1997) guidelines recommend dietary intakes of 200 IU for children and adults 50 years and younger, 400 IU for adults 51-70 years of age, and 600 IU daily for adults over 70. There is a large margin of safety and many experts recommend 800-1000 IU daily for all adults (from all dietary sources). Patients with no sun exposure, who have malabsorption, or those taking seizure medications may require up to 50,000 to 100,000 IU/week.

Vitamin D deficiency is indeed more common than previously thought. It may be present in as much as 21 percent of US adolescents and adults, and closer to 50 percent of the homebound elderly. Simple attention to diet, supplemental vitamins, and sun exposure should provide adequate vitamin D levels.