Serum 25-hydroxyvitamin D declines in elderly subjects. This decrease reflects, in part, a lower vitamin D intake. But changes in serum 25-hydroxyvitamin D are more marked in the northern latitudes of the world because less vitamin D synthesis occurs in the skin as a result of a reduced amount of ultraviolet light. Consequently, vitamin D deficiency leading to osteomalacia is more common in the northern latitudes, particularly among the elderly. The Recommended Daily Allowance of 200 IU of vitamin D in the elderly may be insufficient, since higher doses of 800 IU/day have been shown to reduce the incidence of osteoporotic fractures. The use of more potent analogues of vitamin D, such as calcitriol (Rocaltrol), should be reserved only for those patients who have established vertebral osteoporosis and who generally have more pronounced malabsorption of calcium.
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