Calcium in Food or Supplement Is Safe in Postmenopausal Women

Nancy A. Melville

September 24, 2019

ORLANDO, Florida — Amid the ongoing debate about the risks and benefits of calcium supplementation, a new randomized trial in postmenopausal women comparing dietary versus supplemental calcium over the course of a year shows no differences in measures of cardiovascular risk between the two, nor were there any differences with a control group.

"A 12-month intervention comparing supplemental to dietary calcium intake did not demonstrate a negative impact on vascular health in healthy postmenopausal women, and no significant differences were noted within groups," said first author Suzanne N. Morin, MD, McGill University, Montreal, Quebec, Canada, when presenting the findings here at the American Society for Bone and Mineral Research (ASBMR) 2019 Annual Meeting.

"These data contribute evidence to the short-term safety of these interventions for calcium intake in healthy postmenopausal women."

Longer Studies Still Required?

However, some question whether a 1-year intervention can provide conclusive evidence on the controversial issue.

"I think they've done a good job with this study, but I agree [with some audience member comments] that 1 year is perhaps too short a period to expect that things could change substantially in the blood vessels using the techniques available," session moderator Bente Langdahl, MD, PhD, of Aarhus University Hospital, Denmark, told Medscape Medical News.

"I think longer-term studies are needed for us to be sure," Langdahl added.

"I think we cannot rule out that over a 5- or 10-year period there may be something, but the data are controversial and currently difficult to figure out," she acknowledged. "There is still a question of whether it's completely safe or not, and that applies to supplemental as well as dietary calcium."

Morin noted, however, that previous data have shown any increase in the risk of myocardial infarction seems to manifested early (within 12 to 24 months) following initiation of calcium supplements.

"We felt that if there should be such a serious impact on cardiac events, we would be able to see it in early vascular markers," Morin explained. "We were not able to find any differences in any of the measurements we did."

"Therefore, I am confident that there are no serious and important effects of calcium supplementation, at the dose we gave, in healthy postmenopausal women on vascular health," she said.

Langdahl agreed the data are to some extent "reassuring...there's not a huge acute effect because they would have picked that up."

The study is consistent with the theory of a nutritional threshold, which suggests that once levels of certain nutrients are sufficient, any further benefit of supplementation is not likely to be observed.

"The conclusion I think you can draw from that is if you're healthy and you don't have any bone issues, there is likely no need to increase your calcium intake," Langdahl concluded.

"But if you have osteoporosis, then you should continue to increase your calcium because we know the benefits will certainly overcome whatever risks there may be," she said.

Conflicting Prior Studies but No Difference Seen in Vascular Markers

Because adequate calcium levels are often difficult to achieve through dietary sources, supplements have been recommended, but some studies have suggested they carry a risk for older women.

And several recent reports have even suggested a possible increased in mortality with higher levels of dietary calcium, particularly with milk, and there have also been conflicting studies regarding the association between dietary and supplementary calcium intake and coronary artery calcification, often considered a surrogate prognostic marker for cardiovascular disease risk.

To investigate the issue, Morin and colleagues compared vascular outcomes of 121 healthy, nonsmoking postmenopausal women in Montreal, Quebec, who were randomized for 12 months to 1200 mg daily of calcium through food (n = 48); 750 mg of calcium citrate supplement plus counselling to restrict dietary intake of calcium to 450 mg for a daily total of 1200 mg (n = 47); or a control group, which received no intervention (n = 26).  

All groups received supplemental vitamin D to obtain a total of 800 IU/day.

Exclusion criteria included having a body mass index (BMI) under 19 kg/m2 or over 35 kg/m2, a history of hypertension, diabetes, cardiovascular disease, use of osteoporosis drugs within the last 3 years, or recent use of calcium or vitamin D supplements.

There were no significant differences in baseline characteristics between the three groups, who were a mean age of 60.5 years, had a mean BMI of 25.7 kg/m2, had mean blood pressure levels of 112 mmHg (systolic) and 72 mmHg (diastolic), and had a mean daily dietary calcium intake of 851 mg/day. All were vitamin D sufficient. During the study, milk and milk products were the main sources of calcium.

After 12 months, there were no significant differences between the groups in the primary outcome — change in carotid femoral pulse wave velocity (cfPWV) and carotid intima-media thickness (cIMT), key indicators of vascular health.

In addition, there were no differences between the groups in terms of lipoproteins, C-reactive protein, and systolic blood pressure after a year of follow-up.

Levels of total cholesterol and diastolic blood pressure were slightly but significantly higher in the control group compared with the two intervention groups at 12 months.

Adherence to the study protocol was excellent in all groups and there were no changes in the control group in terms of calcium or vitamin D intake over the course of the study.

There were also no differences in adverse events between the groups, with the exception of constipation and nausea, which were slightly higher in the calcium supplement group, as may be expected with supplementation.

Because the study population was healthy, generalization to an older and more comorbid population is limited, Morin said.

And she did concede the relatively short duration and sample size were limitations of the study.

"We were probably underpowered to detect a small difference between groups," she told Medscape Medical News.

Morin has reported receiving grant/research support from the Dairy Farmers of Canada. Langdahl has reported receiving research funding from Amge, Axellus, Eli Lilly, and MSD, and consulting and speaker fees from Amgen, Eli Lilly, and MSD.

ASBMR 2019 Annual Meeting. Presented September 22, 2019. Abstract 1075.

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