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Letter to the Editor |
Dairy Farmers of Canada 1801 Avenue McGill College Montreal, Quebec H3A 2N4 Canada E-mail: helen{at}dfc-plc.ca
Dear Sir:
Contrary to Hegsted's comment that there is little evidence that high calcium intakes effectively prevent fractures (1), there is ample evidence that such is the case (2–4). In a similar vein, he refers to increasing evidence that diets high in fruit and vegetables are beneficial in preventing fractures, yet the references cited are far from convincing (5–7). Most puzzling is the question, Why do populations who consume low-calcium diets have fewer fractures than do Western societies who consume high-calcium diets?
To begin with, in Western societies with high calcium intakes, the consumers of high-calcium diets are not the women who most need the calcium (8,9). If, as one suspects, the low-calcium consumers referred to are Asian, it must be taken into account that quantification of fractures in many Asian countries has been sporadic at best. Moreover, Asians have some protective factors against hip fractures that whites lack, such as shorter hip axis lengths and smaller frames with lower centers of gravity (10,11). People in Asia tend to lead a more active lifestyle, which helps build strong bones, and they do not have to walk in snowy, icy conditions, which increase the risk of slipping and falling. In addition, Westerners have a higher life expectancy than do people in many Asian countries, allowing greater opportunity to develop osteoporosis (12).
Hegsted's statement that recommended calcium intakes are now so high that it is difficult, if not impossible, to devise practical diets that meet these recommendations is also puzzling. How about the Food Guide Pyramid (13) or Canada's Food Guide (14)? Three daily servings of milk products—for example, an 
236-mL (8-oz) glass of skim milk with breakfast, lunch, and dinner—with a balanced diet yields 1200 mg Ca.
The puzzlement continues with the reference to the unreliability of dietary intakes: the references cited all refer to an underestimation of energy intake, not to intakes of specific nutrients. Surely calcium, coming as it does from one main food group, is much less likely to be inaccurately estimated.
The fact that long-standing recommendations to increase calcium intakes appear to have had little or no effect on the prevalence of osteoporosis or fractures in the United States in no way proves that the recommendations are invalid, anymore than increasing levels of obesity in the United States prove that the long-standing recommendations to reduce fat intake are invalid.
To cite Kanis's assertion (15) that there are no adequately controlled studies to show whether increased calcium intake has an effect on skeletal consolidation or subsequent fracture risk before or after longitudinal growth has ceased is to dismiss the work of many respected investigators in the field, including that of Heaney (3).
Perhaps most puzzling of all is the reference to the Harvard Nurses Health Study (16). First, the results of this study were not statistically significant, but more to the point, why not refer to more recent, contradictory data by the same authors (17)? This 1998 study examined vitamin D receptor genotype and the risk of bone fractures, also using data from the Nurses Health Study. It observed a greater risk of bone fractures for women who were older, leaner, or less physically active or who had low calcium intakes.
In fact, a recent analysis of 139 articles on the role of calcium in skeletal health published over the past 25 y provides convincing evidence for calcium's benefits (3). In all but 2 of 52 investigator-controlled calcium-intervention studies, an increase in calcium intake improved bone balance, increased bone gains during growth, reduced bone loss in later years, or lowered fracture risk. Similar beneficial effects of calcium were found in 75% of 86 observational studies.
Although many factors, nutritional and nonnutritional, contribute to bone health, the beneficial effect of calcium is clearly major. More evidence confirms these results, as noted by Heaney in his recent study (3): "Since submission of this manuscript, 13 additional reports have been published, one metabolic study, 4 randomized controlled trials, and 8 observational studies. All 13 found a benefit from extra calcium."
REFERENCES
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