Older people with high levels of omega-3 fatty acids and vitamins B, C, D, and E in their blood do better on cognitive tests than those with lower levels, according to a new study.

On the other hand, trans fats were found to hurt cognition.

Together, the omega-3s, vitamins, and trans fat levels, as measured by a recently developed blood test, accounted for over 70 percent of the variation in the scores of cognitive tests taken by the study subjects, the researchers reported.

The results show how physicians may be able to help individual patients reach personal dietary goals to help their brain health in their later years, said study author Gene Bowman, an assistant professor of neurology at Oregon Health and Science University.

The study, involving 104 people who were 87 years old on average, was a follow-up to research that indicated that taking blood measurements solves the problem that occurs when people, filling out study questionnaires, inaccurately remember what they've eaten.

"This is a study where we were looking to figure out better ways to study the role of diet and nutrition on healthy brain aging, so we've used blood measures to reflect dietary patterns rather than have people report what they're eating," Bowman said.

The study is published online today (Dec. 28) in the journal Neurology.

Brain food

The study suggests some diet patterns should be avoided to help people stay sharper as they get older. " Trans fats are known to be bad for cardiovascular health, so it's not too much of stretch to think that they're bad for the brain," Bowman said. "It turns out trans fat was actually our most consistent finding in the study."

In addition to the reduced cognitive ability, the researchers found that trans fat consumption correlated with more shrinkage of the brain. 

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"One main thing we can draw from this is it looks like trans fats are a big no-no for brain health," Bowman said.

Researchers not involved in the study said the findings show promise for a new avenue of research, as well as confirming current ideas on maintaining a healthy brain with age.

"I think it's timely in that we have other studies showing a connection between, for example, overweight or obesity and dementia risk," said Dr. Gary Small, director of the UCLA Longevity Center and co-author of "The Alzheimer's Prevention Program" (Workman Publishing, 2011). "You can see there is clearly a connection between what we eat and how well we think as we age."

If confirmed, the findings of the study could allow doctors to determine whether patients with low levels of nutrients should add certain foods to their diet to protect against cognitive decline, Small said.

Improving cognition, preventing dementia

While the study would not change clinical practice in the short term because it still needs confirmation, Small said, it does provide more evidence that food choices can help the brain as we age.

"There are components of a brain-healthy diet that research points to, including omega-3-rich fish and nuts like walnuts, antioxidant fruits and vegetables, whole grains and avoiding processed foods and dairy products and meats rich in omega-6 fats," Small said. "If you look at some of the nutrients measured in this study, it certainly is consistent with what we know about a healthy brain diet."

Bowman said researchers plan to continue to follow their study subjects to look for  changes not only in their thinking abilities, but also in motor functions, such as walking.

While the study is promising, said Christy Tangney, a nutrition researcher at Rush University Medical Center in Chicago, further work is needed for the new biomarkers the researchers measured to be seen as an effective research tool.

While blood markers may overcome the problem of recall on diet surveys, they are not perfect, said Tangney, who wrote an editorial published in the journal with the study.

"I think people think that just because they take a biochemical marker, there's no problem with those," she said.

Tangney said she has sent tubes of her own blood to different labs for tests of nutrient markers and found the results differ enough that a doctor could give different medical advice based on them.

What's needed, said Tangney, is to determine whether these markers correspond with good dietary patterns over the long term, or whether they simply indicate that someone has eaten well over the past few days.

Also, she noted, most of the people in the study were white and well-educated, and so future studies also need to examine a more diverse population.

Following patients long-term also could also clear up some of the other potential problems with the current study, another researchers said.

"The default assumption is that diet is affecting brain aging, but it could also be the case that brain aging is affecting diet," said Rhoda Au, a dementia and aging researcher at Boston University.

Au said that there is also some indication that a very low body weight can hurt  cognition, the result of weight loss and lack of nutrition.

But one of the important findings was that it seemed to be foods in combination, rather than individual vitamins, that were helping brain power, and so recommendations for the future would likely focus on foods rather than vitamin supplements.

"The take-home message from this study is the concept of a balanced diet, rather than a single source of nutrients," Au said.

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