Some older women who take calcium supplements commonly recommended to ward off age-related bone damage may face an increased risk of developing dementia, a small study suggests. The heightened dementia risk appears limited to women who have had a stroke or suffer from other disorders that affect blood flow to the brain, researchers report in the journal Neurology.

“Our study is the first to show a relationship between calcium supplementation and increased risk for dementia in older women,” said lead author Dr. Silke Kern of the University of Gothenburg in Sweden. Still, the findings from this observational study don’t prove calcium supplements directly cause dementia, Kern added by email. Even for women who have had a stroke, it’s too soon to say for sure whether it makes sense for them to avoid calcium supplements, Kern noted. “These findings need to be replicated before any recommendations can be made,” Kern said. Millions of women take calcium supplements to strengthen bones made brittle by osteoporosis, a bone-thinning disorder that typically develops starting during menopause when the body slows production of new bone tissue.

For the current study, Kern and colleagues examined data on 700 women between the ages of 70 and 92 who didn’t have dementia. At the start of the study, and again five years later, women did a variety of psychiatric and cognitive tests including assessments of memory and reasoning skills. A subset of about 450 women also got brain. When the study began, 98 women were taking calcium supplements and 54 participants had already experienced a stroke. During the study, 54 more women had strokes, and 59 women developed dementia. Among the women who had brain scans, 71 percent had so-called white matter lesions, which are signs of mini-strokes and other disorders that affect blood flow to the brain. Overall, women who took calcium supplements were twice as likely to develop dementia as their peers who didn’t, the study found.