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A recent study showed negative effects of vitamin D supplementation, contradicting previous studies. Could the benefits of vitamin D be overstated?
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Accentuating the positive
The story of vitamin D deficiency is enjoying quite a bit of popularity lately. Whether it is overblown or not is hard to say. There is certainly compelling epidemiological evidence linking vitamin D deficiency to a wide range of chronic health problems among adults. The potential of vitamin D supplementation to decrease the risk for major health problems, like diabetes, CV disease and cancer, has been the driving force behind the increased attention from the lay press, as well as the increased amount of research on the topic appearing in scientific literature.
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Since the majority of U.S. adults have insufficient or deficient levels of vitamin D, many physicians may not fully appreciate the potential negative effects of pharmacologic supplementation of vitamin D. Vitamin D taken in excess amounts can certainly cause toxicity, particularly hypercalciuria and hypercalcemia. But there could also be negative effects from excessive blood levels of vitamin D leading to increased bone resorption over time. Still, many experts now believe that the amount of long-term daily vitamin D intake necessary to cause vitamin D toxicity is probably about 10,000 IU daily and maybe even higher. Given that this dose is much higher than the typical recommended supplementation for patients, most physicians have felt that they have been making recommendations for vitamin D intake well within the margins of safety for this vitamin.
It is premature to broaden the conclusions of this one study to think that the typical regimens of vitamin D supplementation (ie, 1,000 IU to 2,000 IU twice monthly) might be harmful to bone quality and bone strength. For now, medical practice should continue to support the notion that reasonable calcium and vitamin D supplementation for patients is part of an overall approach to maintaining good bone health.
Jason Wexler, MD, is an endocrinologist at Washington Hospital Center, Washington, D.C.
The dilemma of dosage
The recent JAMA study used very high doses of vitamin D — 500,000 IU — which is not something we use in clinical practice. The researchers postulated that the high-dose vitamin D may have improved well-being and energy levels, which may have increased the activity level of the subjects receiving the high-dose vitamin D, predisposing them to more falls due to the increased activity. There is some evidence showing that vitamin D is involved in muscle strength.
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We cannot say, based on one study, that high-dose vitamin D leads to fractures. We have previous studies showing that vitamin D decreases the risk of fractures, especially in nursing home residents.
We need more research in this area. Additional light has been shed on vitamin D and malignancy, heart failure, diabetes, metabolic syndrome, obesity and other diseases. Despite that, there is still much more we need to know. Are supplements the answer or should we go back to the natural way of obtaining vitamin D, from the sun and food? There are still more questions that need to be answered. Physicians are more aware of the problem. Testing for the deficiency is relatively easy. Replacement is also readily available.
There are multiple studies showing benefit in regards to bone-density improvement and fracture reduction, especially when combined with calcium. More recent studies have shown concerns about high-dose vitamin D and vascular calcification. Endocrinologists should be aware of these findings and practice caution when prescribing high-dose vitamin D in high-risk individuals with severe vascular disease. Further studies need to be performed to resolve this issue.
Lina Yassine, MD, is an endocrinologist at Saint Matthews Medical Associates, Louisville, Ky.