Does dietary calcium have a protective effect on bone fractures in women? A meta-analysis of observational studies

It is generally accepted that supplemental Ca and/or vitamin D is effective in reducing the incidence of bone fractures; this is supported by numerous randomised controlled trials and meta-analyses. However, a question that has received much less attention is whether dietary Ca, i.e. Ca in physiological doses in normal food intake, also affects bone fracture risk. The present study aims to review the effect of dietary Ca on bone fractures at the hip, spine and radius in women >35 years old, and to compare these results with previous meta-analyses. MEDLINE (1966-1999) and reference lists in papers were searched for observational dietary Ca studies. Data were extracted in duplicate and separately. Heterogeneity and publication bias were tested. Observational studies failed to show any association between dietary Ca intake and risk of hip fracture (risk ratio 1.01, 95 % CI 0.96, 1.07 for each increment of 300 mg dietary Ca intake/d). There is a suggestion that either extremely low Ca intake may increase fracture risk, or that East Asian women may respond differently to increasing Ca intake.