High calcium intake could raise CV mortality in women

A high calcium intake, from diet or the combination of diet and supplements may raise the rate of mortality, especially cardiovascular (CV) mortality, said a study in the British Medical Journal (BMJ).

In an observational cohort study, Swedish researchers followed approximately 61,000 women, aged, on average, 53 years at baseline. Information about dietary and lifestyle habits were assessed by questionnaires. Based on the questionnaire information, calcium intake from diet and supplements was estimated. During follow-up (at about 20 years), 12,000 of the women died. Death rates by calcium intake levels were assessed.

“We found a higher risk of mortality, especially CV mortality with a high calcium intake,” Karl Michaëlsson, clinical professor, Department of Surgical Sciences and Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden, told Formulary.

“On the other hand, we also found a higher risk of mortality associated with a low calcium intake but this latter finding was not confirmed by us in our sensitivity analysis,” he said. “The higher risk of death was seen with a higher dietary calcium intake. This risk increase was modest. If we did not consider the dietary component of calcium intake, we found on average no association with calcium supplement use and mortality.”

However, women who consumed a high dietary calcium intake together with calcium supplements had a higher mortality rate, even though few had this combination in the cohort.

A research group from Auckland, New Zealand, previously published 3 re-analyses of randomized studies in BMJ.  “They have shown a moderate higher risk of CV disease with calcium supplement use,” Michaëlsson said. “In one of their analysis they also considered dietary calcium intake in addition to the calcium supplement.”

They found that the higher risk of CV disease with calcium supplement use was only predominant in combination with a high dietary calcium intake. “However, other researchers have also re-examined their randomized trials and have not found a higher risk of CV disease,” he said. “A complicating fact is that the methodologies of the re-examinations have differed. Cautious interpretation of all observational study results is always needed but our findings fit those from the New Zealand research group.” ■