Increased calcium intake is associated with a lower risk for primary hyperparathyroidism (PHPT), shows research published in the BMJ.
The study also showed that low-dose calcium supplementation could reduce the risk, independent of dietary consumption.
"Paik and colleagues' study provides evidence to support physicians in confidently encouraging female patients to take calcium supplements," writes James Norman (Norman Parathyroid Center, Tampa, Florida, USA) in an accompanying editorial.
Julie Paik (Harvard Medical School, Boston, Massachusetts, USA) and colleagues used data from 58,354 women enrolled in the Nurses' Health Study. Over a follow-up of 22 years there were 277 cases of incident PHPT.
The participants' diet was assessed by a food frequency questionnaire which also asked them about their use of supplements. The authors then divided the women into five equal groups according to their energy-adjusted calcium intake over 1 year of the survey.
Paik and colleagues found that the risk for PHPT was 59% lower in women with the highest total calcium intake (median 1070 mg/day) compared with women with the lowest calcium intake (median 443 mg/day; 45 vs 86 cases).
Both dietary intake and supplementary intake of calcium were independently associated with a reduced risk for PHPT. Women who took more than 500 mg/day supplementary calcium had a significant 59% reduction in risk compared with women who never took supplements. Supplements of 500 mg/day or less also reduced the risk but only by 18%, and this did not reach statistical significance.
The authors explain that the association between calcium intake and PHPT is thought to be because low calcium intake can increase the likelihood of parathyroid adenoma - the most common cause of PHPT. However, they believe this is the first prospective study to directly examine the link.
In his editorial, Norman adds: "Daily calcium supplements in modest doses are likely to provide more benefits than risks given that even mild [PHPT] has important clinical associations and, over many years, even a moderate increase in calcium concentration probably helps reduce the incidence of parathyroid tumors."
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