Higher Calcium Intake May Not Lower Risk for Fractures and Osteoporosis

Gradual increases in dietary calcium intake above the first quintile in a large female cohort are not associated with further reductions in fracture risk or osteoporosis, according to the results of a prospective longitudinal cohort study reported in the May 24 issue of the BMJ.

“It is problematic to make recommendations regarding calcium intake based on the results from clinical trials and previous cohort studies,” write Eva Warensjö, from Uppsala University in Uppsala, Sweden, and colleagues. “Meta-analyses of randomised trials found that supplemental calcium gave modest or no reduction in risk of fracture. Both the habitual dietary intake of calcium and vitamin D status may affect the outcome and are rarely accounted for in the design of calcium supplementation trials.”

The goal of the study was to evaluate associations between long-term dietary calcium intake and the risk for any type of fractures, hip fractures, and osteoporosis. The study cohort consisted of 5022 women who participated in a subcohort of the Swedish Mammography Cohort of 61,433 women in Sweden who were born between 1914 and 1948. This population-based cohort was established in 1987, and participants were followed up for 19 years for primary outcomes of incident fractures of any type and hip fractures, which were identified from registry data.

A secondary outcome in the subcohort was osteoporosis diagnosed by dual energy x-ray absorptiometry. Repeated food frequency questionnaires allowed determination of dietary consumption.

Of 14,738 women (24%) who had a first fracture of any type during follow-up, 3871 (6%) had a first hip fracture. Osteoporosis was diagnosed in 1012 (20%) of the subcohort. For dietary calcium, the risk patterns were nonlinear. In the lowest quintile of calcium intake, the crude rate of a first fracture of any type was 17.2/1000 person-years at risk vs 14.0/1000 person-years at risk in the third quintile, yielding a multivariable adjusted hazard ratio (HR) of 1.18 (95% confidence interval [CI], 1.12 – 1.25). For a first hip fracture, the HR was 1.29 (95% CI, 1.17 – 1.43), and the odds ratio for osteoporosis was 1.47 (95% CI, 1.09 – 2.00).

The fracture rate in the first calcium quintile was more pronounced with a low vitamin D intake. Although the highest quintile of calcium intake did not further lower the risk for fractures of any type, or the risk for osteoporosis, it was associated with a higher rate of hip fracture (HR, 1.19; 95% CI, 1.06 – 1.32).

“Gradual increases in dietary calcium intake above the first quintile in our female population were not associated with further reductions in fracture risk or osteoporosis,” the study authors write.

Limitations of this study include possible residual confounding; limitations inherent in dietary assessment methods; observational design, precluding conclusions regarding causality; and lack of generalizability to other people of different ethnic origins or to men.

“Dietary calcium intakes below approximately 700 mg per day in women were associated with an increased risk of hip fracture, any fracture, and of osteoporosis,” the study authors conclude. “The highest reported calcium intake did not further reduce the risk of fractures of any type, or of osteoporosis, but was associated with a higher rate of hip fracture.”

The Swedish Research Council supported this study. The study authors have disclosed no relevant financial relationships.