Although randomized clinical trials have demonstrated a modest benefit of calcium intake on bone mineral density (BMD), most observational studies have found no correlation between calcium intake and BMD changes. The medical community has interpreted this discrepancy to mean that nutritional calcium deficiency may be corrected with calcium supplementation. Therefore, most recommendations for postmenopausal women suggest they should consume more than 1,500 mg of calcium daily to reach neutral bone balance.
Sara M. Bristow, PhD, a research fellow at the University of Auckland, New Zealand, and colleagues investigated this recommendation, determining the relationship between dietary calcium intake and rate of bone loss in older postmenopausal women. They found dietary calcium intake was not associated with postmenopausal bone loss. The results of their six-year, longitudinal study were published online March 21 in The Journal of Clinical Endocrinology & Metabolism.1
The cohort included 698 osteopenic postmenopausal women older than 65. Although the women were aware their baseline bone density was in the osteopenic range, they were not informed of their individual BMD values. All participants took vitamin D, but not calcium supplements. The researchers documented the calcium intake of each participant’s self-reported diet.
The women had a mean daily calcium intake of 886 mg and were grouped for analysis into quintiles, with the means for the first and fifth quintiles being 414 and 1,435 mg per day, respectively. The investigators found baseline BMDs were not related to the quintile of calcium intake before and after they adjusted for baseline age, height, weight, physical activity, alcohol intake, smoking and past hormone replacement use.
Next, the researchers performed a six-year longitudinal analysis of the women, during which they found dietary calcium intake declined by 40 mg per day from baseline. The team also performed sequential measurements of total bone mineral to estimate changes in bone balance over time. They found total body bone balance was unrelated to an individual’s calcium intake. Moreover, although 95 women experienced at least one fragility fracture during the study, the investigators found no relationship between the quintile of calcium intake and fracture.
“Mean calcium intake in our population was 886 mg per day, similar to that in previous studies of postmenopausal women in New Zealand, the U.S. and Australia,” write the authors in their discussion. “It is uncertain whether our findings will apply to populations with much lower intakes. For example, in 6,200 Chinese adults with a mean calcium intake [of approximately] 400 mg per day, fracture risk was increased among men with intakes [less than] 275 mg per day, but not among women.”
The current findings reinforce the growing understanding that increases in dietary calcium intake are unlikely to affect the prevalence of and morbidity from postmenopausal osteoporosis. Thus, the authors suggest the advice provided to the public with regard to calcium intake be revised to incorporate this new information.
Lara C. Pullen, PhD, is a medical writer based in the Chicago area.
- Bristow SM, Horne AM, Gamble GD, et al. Dietary calcium intake and bone loss over 6 years in osteopenic postmenopausal women. J Clin Endocrinol Metab. 2019 Mar 21. pii: jc.2019-00111. [Epub ahead of print]