By Kathryn Doyle
(Reuters Health) - Older people who eat healthy, with more fruits and vegetables, nuts and fish in their diets, may be less likely to experience declines in thinking and memory over time, according to a new international study.
"It is likely that a healthy diet has effects on cardiovascular risk factors and cardiovascular disease, and that this is an important mechanism for reducing the risk of cognitive decline," said lead author Andrew Smyth of McMaster University in Hamilton, Ontario, Canada, and the National University of Ireland in Galway.
The results were similar when researchers excluded people who had overt clinical events like stroke, suggesting that the benefit may also reduce the risk of cognitive decline for people without such clear indicators of advanced cardiovascular disease, Smyth told Reuters Health by email.
"As our study is observational, we can only say that a healthy diet was associated with a reduced risk of cognitive decline and cannot definitively say there is a causal relationship," he said.
Smyth and his coauthors used data from two multinational randomized trials of a blood pressure medication. They included more than 27,000 men and women age 55 and older who had a history of coronary, cerebral or peripheral artery disease or high-risk diabetes and who were followed until death, stroke, heart attack or hospitalization. Half the participants were followed for less than five years.
Participants filled out a 20-point food frequency questionnaire at the beginning of the trials and completed a mini-mental state exam at least twice during their respective trials.
Of the 27,000 total participants, 4,699 or almost 17 percent experienced marked cognitive decline based on their mental state exams.
The researchers used the food frequency questionnaire to estimate how "healthy" people's dietary habits were, awarding higher scores to frequent consumption of foods like vegetables, fruits, nuts, soy proteins and fish.
The top fifth of people with the healthiest diets were about 24 percent less likely to experience cognitive decline during the study than the bottom fifth with the worst diet scores, the study team reports in Neurology.
"Our study shows that those with the healthiest diet tended to be more active, were less likely to smoke and had lower body mass index," Smyth said. "This suggests that the consumption of a healthy diet is likely to be associated with a healthy lifestyle in general."
About 14 percent of people in the healthiest diet category had cognitive decline compared to 18 percent of those in the least-healthy category after taking physical activity, high blood pressure and cancer history into account.
"As foods and nutrients are not consumed in isolation, and the reduction in intake of one food usually results in increased intake of other foods, we think that rather than focus on particular foods, it is more important to focus on overall diet quality," Smyth said. "For example, some of the reported benefits of 'healthy' food choices may be lost by 'unhealthy' choices."
The study was not designed to quantify how much or little people should change their lifestyles to lower cognitive decline, and there is no easy way to infer such a conclusion, said Cecilia Samieri, a researcher at INSERM and Universite de Bordeaux in France who was not part of the new study.
"It is interesting to notice that people in the top 20 percent of adherence to healthy diets only appear to be protected, while those with milder adherence are not," Samieri told Reuters Health by email.
All study participants were at high risk for cardiovascular disease, so the results may not be generalizable to the broader population, she noted.
"Indeed, to be included in the study, participants had to report a history of cardiovascular disease or of diabetes, and they may have modified their diets after the diagnosis, along with being more at risk to experience accelerated cognitive decline during follow-up," she said.
SOURCE: http://bit.ly/1F8awwC Neurology, online May 6, 2015.