Calcium supplements linked to post-stroke dementia in women

"Calcium supplements could dramatically raise the risk of dementia in women who suffer a stroke, a new study found," the Mail Online reports. However, the sample size (98) of women taking supplements was small, which casts doubts on the reliability of the claims.
 
The Swedish study included 700 women aged over 70 without dementia, 98 of whom were taking calcium supplements (we assume due to concerns about osteoporosis, though this was not discussed in the study). After five years, 14.3% of women who'd taken supplements had developed dementia, compared to 7.5% of women who didn't – about double the risk, after taking other factors into account.

Further analysis showed that the raised risk only applied to women who had already had a stroke, or who had signs of damage to blood vessels in their brain on scans. However, this was based on just six out of 15 women with a history of stroke and 50 out of 316 with signs of blood vessel damage who had taken calcium supplements.

The researchers say that because their study is "relatively small" and an observational study, their findings need to be confirmed. They don't call for any immediate action as a result of their findings.

It is possible to increase calcium levels through diet alone. Foods such as dairy products, green leafy vegetables, soya beans and nuts are good sources of calcium. Read more about ways to improve bone health.

Where did the story come from?

The study was carried out by researchers from the University of Gothenburg in Sweden and University College London, and was funded by grants from many different organisations, including the Swedish Research Council. The study was published in the peer-reviewed journal Neurology.

The coverage in the UK media was at times alarmist. While the Daily Telegraph took a more measured approach, the Mail's headline goes as far as telling people who've had a stroke to avoid calcium supplements; something that the researchers do not do.

Both reports made clear the distinction between calcium in foods such as milk and green leafy vegetables – which is not thought to have risks – and calcium supplements. However, neither reported the small number of women on which the main results were based. 

What kind of research was this?

This was a population-based cohort study, which followed a group of women over time. Cohort studies are good at showing links between factors (in this case, calcium supplements and dementia) over time. On their own they cannot show that one factor causes another and may be subject to other confounding factors, where other unmeasured risk factors may be contributing to the effect seen. 

What did the research involve?

Researchers followed 700 women from a larger population study in Sweden, all of whom were aged 70 to 92 and free of dementia at the start of the study. They were tested for dementia, and some had brain scans to look for signs of cerebrovascular disease (which includes stroke and so-called white matter lesions, areas of the brain which have poor blood flow), which is associated with vascular dementia. They were asked about use of medicines and supplements, including calcium. They were tested again for dementia five years later.

CT scans were used to look for brain lesions in 447 of the women at the start of the study, but were not repeated at the end. The women were tested using standard diagnostic criteria for dementia, by psychiatric nurses. Of the 700 women at the start of the study, 64 died and 105 did not take part in the follow-up. Nine of these women had dementia diagnoses in the Swedish Hospital Discharge Registry, so were included in the follow-up data.

The researchers analysed their data in a number of ways. They looked first at risk of any type of dementia for all women who'd taken calcium supplements, and then at particular types of dementia. Alzheimer's disease is the best-known type of dementia, but vascular dementia, caused by a series of mini-strokes, is also common. Some people have signs of both Alzheimer's and vascular dementia.

Researchers grouped together vascular dementia and mixed dementia into one group of stroke-related dementia. They also looked at risks for different groups of women: those who'd had a stroke, those whose CT scans showed white matter lesions, and those with no signs of cerebrovascular disease. They adjusted their figures to take account of confounding factors likely to affect dementia risk, including age, education, hormone use and genes known to influence Alzheimer's disease.

What were the basic results?

Of the 700 women in the study, 59 developed dementia. Overall, women who took calcium supplements were twice as likely to develop dementia as those who did not (odds ratio (OR) 2.10, 95% confidence interval (CI) 1.01 to 4.37). This risk was more pronounced for stroke-related dementia (OR 4.4, 95% CI 1.54 to 12.61).

Importantly, closer analysis of the figures showed that taking calcium did not increase risk of dementia for women who'd not had a stroke or who had no signs of white matter lesions on their brain scans. For women who'd had a stroke, taking calcium supplements was linked to an almost seven-fold increase in the chances of getting dementia, but this was based on six women who took supplements out of 15 who had a stroke (OR 6.77, 95% CI 1.36 to 33.75). There was an almost three-fold increase in risk of dementia for women with white matter lesions, based on 50 of 266 women taking supplements (OR 2.99, 96% CI 1.28 to 6.96).

How did the researchers interpret the results?

The researchers were cautious in their conclusions, saying: "Calcium supplementation may increase the risk of developing dementia in elderly women with cerebrovascular disease." However, they added: "Because our sample was relatively small and the study was observational, these findings need to be confirmed."

Conclusion

The media paint this as a troubling study for older women who take calcium to strengthen their bones. However the small size of the study (only 98 women took calcium supplements, and only 14 of those got dementia) and its observational nature mean that we cannot rely on the results.

As the researchers mention, it is possible that those taking supplements were less healthy than those that didn't in some unmeasured way. Further research may improve our confidence in these results.

Broken bones are not a trivial matter for older people – a broken hip can be the difference between being able to live independently and needing to go into a nursing home.

Questions were raised last year, as we discussed at the time, about how well calcium supplements work to reduce the risk of broken bones, when two studies published in the BMJ showed they may not provide much protection for most people. However, these studies mostly looked at healthy adults aged 50 and over, not people being treated for weak bones.

The UK government currently recommends getting 700mg of calcium daily, and says a healthy, varied diet is likely to provide this for most people.

Good sources of calcium include:

• milk, cheese and other dairy foods
• green leafy vegetables – such as broccoli, cabbage and okra, but not spinach
• soya beans
• tofu
• soya drinks with added calcium
• nuts
• bread and anything made with fortified flour
• fish where you eat the bones – such as sardines and pilchards

If you need higher levels of calcium, you might need to take supplements, but it is best to talk to your GP first.