Despite some evidence to the contrary, people's blood levels of calcium and vitamin D may be unrelated to their thinking, memory and other brain functions, a new study suggests. The findings, based on a government health study of Americans ages 20 to 90, bolster past evidence showing no association between vitamin D levels in the blood and cognitive function.
They also cast doubts on recent research that has linked higher calcium levels to a quicker mental decline in older adults. "Although some recent data suggest that even moderately elevated (blood) calcium levels may be related to impaired cognitive performance, the results of this study do not support these results," researcher Dr Anna-Maija Tolppanen, of the University of Bristol in the UK, noted in an email to Reuters Health.
The findings also back up a previous analysis of the same study cohort done by a different research team. That study found no association between higher vitamin D levels and better cognitive performance in young or older people.
Overall, the current results "do not support an important role" for either calcium or vitamin D in adults' cognitive function, Tolppanen and her colleagues report in the journal Epidemiology.
In theory, calcium levels could affect cognitive performance or the odds of age-related cognitive decline. Disruptions in the body's calcium balance can contribute to nerve cell damage; and in people with hyperparathyroidism - a hormonal disorder that raises blood calcium - normalising calcium levels can correct memory problems and other cognitive symptoms of the disorder. Similarly, vitamin D, which helps regulate calcium levels, could theoretically affect cognition. But studies looking at the relationship have been mixed, with some linking higher vitamin D levels to greater cognitive performance and others showing no such connection.
As for calcium, two studies that followed older adults over time found that those with higher blood calcium levels tended to show greater cognitive decline. However, the current study appears to be the first to examine calcium levels and cognitive function in younger adults. This is important, Tolppanen explained, because if there is a link among younger people, it would be less likely to reflect so-called "reverse causality" - that is, people with poorer cognitive function making diet or other behaviour choices that affect their calcium levels. Overall, Tolppanen and her colleagues found no association between blood calcium levels and performance on standard cognitive tests among either younger or older adults in their study. The same was true of vitamin D levels.
The findings do not rule out a connection between the nutrients and mental performance. A limitation of the study is that participants were assessed at one time point; so-called prospective studies, which would follow people over time to see how vitamin D and calcium levels correlate with changes in cognitive test performance, would be more informative. Larger prospective studies are still needed, according to Tolppanen.
The findings are based on data from a government health study conducted between 1988 and 1994. There was information on blood calcium levels and cognitive test performance for about 4,400 adults ages 20 to 59, and 4,300 adults ages 60 to 90; information on vitamin D levels and test performance was available for roughly 4,800 adults in each age group.
In a previous analysis of the same group, another research team had found no association between higher vitamin D levels and better cognitive performance - a finding that was in contrast to those of some, though not all, earlier studies.
That raised the question of whether the lack of a link was due to a "masking" effect by blood calcium. Because blood calcium levels are partly regulated by vitamin D, it's possible that any effects of calcium on cognitive function could obscure those of vitamin D.
However, Tolppanen said that even when variations in people's blood calcium were taken into account, there was no association between vitamin D and cognition in this study.
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