A new epidemic of vitamin D deficiency

Townsend Letter for Doctors and Patients,  July, 2004  by Alan R. Gaby

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The widely circulated rumor that Kurt Vonnegut told newly graduating MIT students to "wear sunscreen" is actually a myth. Had he really made such a recommendation, it would have been necessary for his "Breakfast of Champions" to include a vitamin D supplement.

Vitamin D deficiency appears to be an increasingly prevalent, but largely unrecognized, problem. According to various studies, the prevalence of vitamin D deficiency ranges from 4.2% to greater than 90%, depending on the race, health, and lifestyle of the people surveyed, their geographic location, and the criteria used to diagnose deficiency. While it is well known that severe vitamin D deficiency causes rickets, osteoporosis, and osteomalacia, it is not generally known that even a mild deficiency may cause such problems as muscle weakness, fibromyalgia, impaired balance, and depression.

In the course of human evolution, the main source of vitamin D has been exposure to sunlight. Ultraviolet B (UVB) light from the sun stimulates the synthesis of vitamin D from a precursor molecule in the skin. Food, on the other hand, is a relatively poor source of the vitamin; only cod-liver oil, oily fish, and vitamin D-fortified dairy products provide more than trace amounts. With respect to vitamin D-fortified milk (the main food source of the vitamin for many people), many commercial brands of milk contain less than the label indicates. In one study, 26 of the 42 milk samples (62%) contained less than 80% of the amount of vitamin D claimed on the label, and no vitamin D was detected in 3 of the 14 samples of skim milk tested. (1)

Because most diets do not provide adequate amounts of vitamin D, people who do not receive enough sun exposure are at risk of developing a deficiency. Those with dark skin and elderly people are at greatest risk, because they have a reduced capacity to synthesize vitamin D in response to sunlight exposure. In addition, people who live above 35 degrees latitude or in areas with a lot of atmospheric pollution may not obtain adequate amounts of UVB, even if they do go out in the sun. In modern America, most work and leisurely activity is done indoors. Because of the fear of developing melanoma, other skin cancers, or wrinkles, many people purposely avoid the sun, or else block the beneficial UVB by applying sunscreen to their body. While excessive sun exposure is certainly unwise, sunlight deficiency seems to be an ever-increasing problem.

Several years ago, five patients were reported with severe myopathy associated with vitamin D deficiency. (2) Each of these patients had been confined to a wheelchair because of severe weakness and immobility. In all five patients, treatment with high-dose vitamin D for 4 to 6 weeks resulted in a resolution of body aches and pains and a return of normal muscle strength. In each case, vitamin D deficiency had not been suspected initially, and the symptoms had been attributed to other causes.

Vitamin D deficiency also might be a contributing factor to depression, particularly seasonal affective disorder (winter depression), which occurs during the time of the year when vitamin D levels are the lowest. In a small randomized trial, administration of a single 100,000-IU dose of vitamin D was more effective than a month of daily phototherapy (light therapy) in patients with seasonal affective disorder. (3) Moreover, in the group treated with phototherapy, there was a significant correlation between the improvement of depression and the improvement in vitamin D status. That observation suggests that the effectiveness of phototherapy in cases of seasonal affective disorder is due at least in part to an increase in vitamin D synthesis in the skin.

Fibromyalgia and generalized aches and pains have also been attributed by some investigators to vitamin D deficiency. In a recent study of 150 residents of Minneapolis, Minnesota, who presented with persistent, nonspecific musculoskeletal pain, 93% were found to have either marginally (65%) or severely (28%) deficient serum concentrations of 25-hydroxyvitamin D. (4) The patients in this study were not given vitamin D supplements, so a cause-effect relationship between their symptoms and vitamin D deficiency was not established. However, in a study of 299 patients in Saudi Arabia with chronic low back pain associated with abnormally low serum levels of 25-hydroxyvitamin D, supplementation with vitamin D for 3 months resulted in clinical improvement in every case. (5)

Numerous studies have shown that vitamin D supplementation helps prevent age-related bone loss and reduces the risk of fractures. Part of the benefit of vitamin D in relation to fracture prevention appears to be due to an improvement in balance and/or muscle strength, which leads to fewer episodes of falling. In a double-blind study, supplementation of elderly individuals with 800 IU per day of vitamin D reduced body sway (a measure of balance) and reduced the frequency of falling by 47%, compared with a placebo (p < 0.04). (6)