Some older women who take calcium supplements may face an increased risk of developing dementia, a small study suggests.

The heightened risk appears limited to women who have had a stroke or suffer from 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 Silke Kern of the University of Gothenburg in Sweden.

Still, this observational study doesn’t prove that 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 they should avoid calcium supplements, she noted.

“These findings need to be replicated before any recommendations can be made,” Kern said.

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Millions of women take calcium supplements to strengthen bones made brittle by osteoporosis, a bone-thinning disorder that typically starts to develop 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 scans.

When the study began, 98 women were taking calcium supplements and 54 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 what is 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. But the increased risk appeared limited to people who had had a stroke or other signs of existing cerebrovascular disease. For women with a history of stroke, the dementia risk was almost seven times higher if they took calcium supplements than if they didn’t.

When women had white matter lesions that can be a precursor to strokes, the dementia risk was three times greater when they took calcium supplements.

Among women without a stroke history or white matter lesions, however, there wasn’t any increased dementia risk associated with calcium supplements.

Beyond its small size, other limitations of the study include the lack of follow-up brain scans at the end of the study, which made it impossible to assess how calcium supplements may have influenced the development of white matter lesions or strokes that went unnoticed.

In addition, the study didn’t look at how much calcium women got in their diets, which can affect the body differently than supplements and is thought to be safe or even protective against blood flow problems, the authors note.