Applied nutritional investigationAssociation of total calcium and dietary protein intakes with fracture risk in postmenopausal women: The 1999–2002 National Health and Nutrition Examination Survey (NHANES)
Introduction
Studies on whether calcium reduces the risk of fracture in elderly women have been inconsistent. Several prospective studies and randomized trials on calcium intake and risk of fracture have not supported a beneficial effect for calcium in reducing risk [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], but several other studies have supported a positive relation [12], [13], [14], [15], [16], [17].
A threshold for calcium's effect may exist, i.e., beyond a particular value there is no additional benefit from ingesting this mineral. However, the precise location of the threshold for fracture reduction is uncertain [18], [19], [20]. In one study, Looker et al. [11] examined the possibility of a threshold effect and linear trend of dietary calcium on fracture risk using cutpoints of <400, >600, >800, and >1000 mg/d, but they did not find a clear support for a threshold in women and a dose–response effect. Women with a daily intake <400 mg, however, were likely to reduce bone loss by increasing their supplemental calcium intake to 800 mg/d [18]. According to the Food and Nutrition Board of the National Academy of Sciences [21], women ≥50 y of age should ingest 1200 mg of calcium per day, but the unresolved critical issue is whether this amount of intake is sufficient to reduce rates of fracture.
Calcium and protein are major components of bone tissue [22], [23], and previous studies have shown positive and negative effects of dietary protein on bone health or risk of fracture [4], [7], [22], [23], [24], [25], [26], [27], [28]. The impact of dietary protein on the skeleton appears to be favorable in older people who are meeting their requirements for dietary calcium but not in those with lower intakes [22].
The present study examined the association of total calcium with risk of fracture in postmenopausal women ≥50 y of age by using data from the 1999–2002 National Health and Nutrition Examination Survey (NHANES). We also assessed the effect of calcium intake on fracture in the presence of various levels of dietary protein intake (DPI).
Section snippets
Data source
The Centers for Disease Control and Prevention's NHANES is designed to assess the health and nutritional status of adults and children in the United States and is unique in its combination of interviews and physical examinations. The NHANES is a nationally representative sample of the non-institutionalized U.S. civilian population obtained using a complex, stratified, multistage sample design [29]. The examination protocol and data collection method are fully documented in the NHANES Dietary
Weighted mean TCI and DPI
In the study population of 2006 postmenopausal women (mean age 67.7 ± 10.1 y), mean TCIs were 264, 722, and 1723 mg/d for TCI categories <400, 400–<1200, and ≥1200 mg/d, respectively (Table 1). Mean TCIs were 836 mg/d for those with fracture, 784 mg/d for those without fracture, 861 mg/d for those with one fracture, and 743 mg/d for those with at least two fractures. Mean DPIs per day were 58 g for those with fracture, 62 g for those without fracture, 59 g for those with a single fracture, and
Discussion
In this cross-sectional study of postmenopausal women ≥50 y old, we found no association between TCI and risk of fracture. Perhaps surprisingly, however, a higher TCI had a significant adverse effect on risk of fracture if DPI was <46 g/d.
Some longitudinal studies have found no evidence that intake of calcium is associated with risk of fracture [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [27]. For example, the Randomised Evaluation of Calcium Or Vitamin D group [1] did not find
Conclusion
Our study indicates that there is no relation between TCI and risk of fracture in postmenopausal women ≥50 y old. Adequate calcium intake in the presence of inadequate dietary protein might not have a beneficial effect on the reduction of fracture. We suggest that the optimal proportion of TCI and DPI needs to be determined for reduction of fracture risk in future studies.
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