The current study had some strengths compared to previous studies in this area, including the large number of participants, the long-term follow-up, the large number of confirmed cardiovascular events (2,709 heart attacks and 1,856 strokes; confirmed by medical record review), detailed information about diet and other cardiovascular disease risk factors, and repeated assessment of calcium supplement use over the 24-year follow-up period. A number of limitations should be considered however, including the possibility of residual confounding, the possibility that vitamin D intake was under-reported (many calcium supplements also contain this), and the fact that the study population was female and almost entirely white, so the findings may not be generalisable to men or other races.
Previous studies have suggested that calcium supplements may increase risk of cardiovascular disease, but the data have been inconsistent. The authors say that their findings do not support the hypothesis that calcium supplement intake increases CVD risk in women, and they call for additional prospective cohort studies examining potential CVD risk associated with calcium supplement use. To date, no RCT has tested the effect of calcium supplementation on CVD as its primary endpoint, and the authors say that any future randomised trials of calcium supplementation should be designed to optimise assessment of CVD events.