The state of vitamin D nutrition depends on synthesis in the skin under the influence of sunlight as well as on dietary intake. In European countries that do not fortify milk with vitamin D, reduced sun exposure is the major factor leading to a fall in body stores of vitamin D with age and to a high frequency of hypovitaminosis D in the elderly sick. In the US, because vitamin D is added to milk and the use of vitamin D supplements is more common, the dietary intake of vitamin D is relatively more important than in Europe, and the total vitamin D intake and body stores of vitamin D are generally higher. Nevertheless, body stores of vitamin D probably fall with age in the US as they do in Europe, and it is likely that some sick elderly persons in the US, especially among those confined to institutions, become vitamin D deficient. For several reasons, the vitamin D requirement increases with age, and a total supply of 15 to 20 micrograms/day (600 to 800 IU) from all sources is recommended. Special attention should be paid to persons most likely to need supplementation, such as the housebound, persons with malabsorption, and persons with interruption of the enterohepatic circulation. Osteomalacia, the bone disease produced by severe vitamin D deficiency, is less common in the US than in Europe, but subclinical vitamin D deficiency may contribute to the pathogenesis of hip fractures, both through increased liability to fall and through PTH-mediated bone loss. The extent to which vitamin D deficiency contributes to hip fractures in the US is unknown, and is an important area for future research. Excess intake of vitamin D or of its metabolites may result in hypercalcemia and extra-osseous calcification, particularly in arterial walls and in the kidney, leading to chronic renal failure. The dose of vitamin D that causes significant hypercalcemia is highly variable between individuals but is rarely less than 1000 micrograms/day. Smaller doses can cause hypercalciuria and nephrolithiasis and possibly impaired renal function. Vitamin D administration may raise plasma cholesterol but there is no convincing evidence that the risk of myocardial infarction is increased. The recommended total supply for the elderly of 20 micrograms/day is most unlikely to be harmful, except in patients with sarcoidosis or renal calculi.

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The average elderly person is in negative calcium balance and accordingly is losing bone mass. While factors such as decreased mechanical loading of the skeleton undoubtedly figure in this age-related loss, a growing body of evidence suggests that inadequate calcium intake may contribute to this loss. On any given day men and women in the US 65 yr or older ingest about 600 and 480 mg calcium, respectively. Calcium intake in the elderly is less than in the young, and reduced absorption efficiency further lowers effective intake. Additionally, other nutrients such as protein and fiber, taken in excess, effectively increase the calcium requirement. Estrogen withdrawal at menopause leads to a decrease in intestinal calcium absorption efficiency and in renal calcium conservation, both effects equivalent to an effective increase in calcium intake requirement. Thus it is not surprising that all studies of mean requirements for zero balance performed in elderly subjects have yielded values above the current RDA for the US. The available evidence thus suggests that the RDA for adults should surely not be lowered below its current level (800 mg), but that, instead, it ought to be raised. It is not possible to say with certainty to exactly what level, but available evidence is compatible with allowances of at least 1200 to 1500 mg/day. Further, the evidence indicates that the mean requirement ought to be thought of as a complex function of age, sex, absorption efficiency, intake of protein, fiber, and probably other nutrients, estrogen status, and mechanical loading. Extensive experience with calcium supplements indicates that daily intakes up to at least 2.5 g of elemental calcium are quite safe in all persons except for certain subsets of the population uncommon among the elderly (eg, those with sarcoidosis, active tuberculosis, or other absorptive hypercalciuric syndromes). At the same time it must be said that osteoporosis is a complex, multifactorial disorder, and that factors unrelated to calcium nutrition undoubtedly play important, even dominant roles in many--perhaps most--osteoporotics. The available evidence, taken together, does not indicate that raising calcium intake will abolish the problem of osteoporosis. It does indicate, however, that calcium nutrition is considerably more important in the genesis of osteoporosis than has been commonly thought for the past 35 yr. As our listing of "important issues" indicates, the full extent of that importance, in both pathogenesis and prophylaxis, remains to be elucidated.(ABSTRACT TRUNCATED AT 400 WORDS)

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