Researchers found that women who had previously had a stroke and who regularly took calcium supplements at the start of the study were seven times more likely to develop dementia over the five-year period than women who had had a stroke but who did not take those supplements.
Additionally, the researchers found that women who had signs of a disorder that affects blood flow in the brain and who regularly took calcium supplements were twice as likely to develop dementia over five years as women who had signs of this disorder but did not take those supplements.
However, while the study shows a link between taking calcium supplements and a higher risk of dementia in some women, it does not prove that taking calcium supplements causes dementia, said study co-author Dr. Silke Kern, a neuroscience researcher at the University of Gothenburg in Sweden. More research is needed before any recommendations for women regarding the potential risks of taking calcium supplements can be made, Kern said.
In the study, the researchers looked at the medical history of 700 women between ages 70 and 92 who did not have dementia at the start of the study. The researchers asked the women if they were regularly taking calcium supplements and tested their memory and thinking skills. The scientists also scanned the brains of 447 of the participants.
The researchers found that 54 women had had a stroke before the study started, and 98 women were taking calcium supplements at the start of the study.
Among the women who had their brains scanned at the start of the study, 71 percent had lesions on their brains’ white matter, which is a marker for cerebrovascular disease — a group of disorders that affect blood flow in the brain. Such lesions are common in older adults, with one review study estimating that anywhere from 50 percent to 98 percent of elderly adults may have them.
The researchers then followed all the women for five years, and found that 59 women developed dementia, and 54 women had strokes during this time period, according to the findings, published today (Aug. 17) in the journal Neurology.
When the researchers looked at the relationship between taking calcium supplements at the start of the study and the women’s risk of developing dementia during the study period, it turned out that this risk was higher, but only for the women who had signs of cerebrovascular disease at the start of the study or who had previously had a stroke. (Cerebrovascular disease is sometimes defined to also include stroke. But in this study, the researchers did not include stroke in their definition of cerebrovascular disease, and only included other types of cerebrovascular diseases.)
For example, six of 15 women who had previously had a stroke and took calcium supplements developed dementia during the study period. In comparison, a smaller proportion — 12 out of 93 women who had previously had a stroke but did not take supplements — developed dementia during the same time period.
The researchers said that they don’t know for sure why the use of calcium supplements may be linked to a higher risk of dementia in women with these conditions. “The mechanism for the harmful effect of calcium supplementation is not fully understood,” Kern told Live Science. However, it may be that calcium supplements affect blood vessels and thus even potentially alter the flow of blood in these vessels, Kern said. Previous research has linked problems with blood vessels to a greater risk of dementia.
Dr. Marc Gordon, chief of neurology at Zucker Hillside Hospital in Glen Oaks, New York, who was not involved in the study, also said that it is too early to determine whether calcium supplements might directly cause dementia in some women. The numbers of women who were taking supplements in the study were small, he said.
Future studies with more participants should be conducted, he said. “All of that said, I think it raises a concern that there is certainly a rationale for thinking that calcium supplements could have an adverse effect on outcomes, particularly in women with cerebrovascular disease,” he said.
“People have a tendency to assume that dietary supplements are automatically innocuous, [but] high levels of supplementation as opposed to just dietary intake [of calcium] could conceivably have some deleterious effects,” he said.