July 23 (HealthDay News) -- Men and women suffering from coronary heart disease seem to fare worse on measures of cognitive function.

And the longer the person had had heart disease, the worse the performance in such mental processes as reasoning, vocabulary and verbal fluency, according to a study in the July 23 issue of the European Heart Journal.

The research, however, had some limitations that may affect its value.

"It's a very well-designed study with a very large number of individuals, so they were able to appreciate small differences in cognitive function," said Dr. Kathryn J. Kotrla, chairwoman of psychiatry and behavioral science for the Texas A&M Health Science Center College of Medicine. "But they didn't control for some key variables such as alcohol and tobacco, which are well-known to impact blood vessel disease. Also depression, which is linked to both coronary heart disease and cognitive functioning."

"This makes the study tantalizing but incomplete," Kotrla added.

Previous studies have given conflicting results regarding the relationship between heart disease and cognitive function. Some have found coronary heart disease (CHD) to be a risk factor, while others have not.

According to the researchers, from University Hospital London and INSERM in France, this is the first large study to look at the association. And, previously, research had focused more on cerebrovascular disease (which includes stroke) rather than just CHD, even though CHD is responsible for most cardiovascular disease. That prior research had found a strong relationship between cerebrovascular disease and cognitive deficit and dementia.

The researchers looked at almost 6,000 British civil servants, aged 35 to 55 at the beginning of the project, taking part in a long-term study.

Both men and women with a history of CHD turned up lower scores for reasoning, vocabulary and overall cognitive function when compared with people who did not have CHD. Women had added problems in verbal fluency.

Men who experienced their first CHD more than a decade prior had even lower scores for reasoning, vocabulary and semantic fluency (categorizing words).

The risk of declining performance in the realm of reasoning went down by about 30 percent for every five years after a diagnosis of CHD.

Women with a longer history of CHD showed a trend for lower scores in semantic fluency, but the data here was based on a smaller number of people.

The authors don't yet know what the biological mechanisms behind this connection might be.

Also unclear from the study was how these changes in cognitive performance affected actual day-to-day function and quality of life, Kotrla said.

But the take-home message is still a familiar one: People should focus on preventing CHD by not smoking and avoiding or controlling diabetes, high cholesterol and high blood pressure. And the focus should start early, before it's too late.

SOURCES: Kathryn J. Kotrla, M.D., chairwoman, psychiatry and behavioral science, Texas A&M Health Science Center College of Medicine, and associate dean, health science center, Round Rock campus; European Heart Journal