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Researchers from the University of New Hampshire, Tufts University and the University of Massachusetts Lowell looked at data from the Boston Puerto Rican Health Study, whose participants ranged in age from about 55 years old to slightly more than 60. The researchers’ goal was to look at individual types—or ‘species’—of fatty acids to see how these levels correlated with cognitive measures. The blood levels were measured by OmegaQuant, an analytical testing firm headed by Omega 3 Index cofounder William Harris, PhD.
“Polyunsaturated fatty acid (PUFA) consumption is recommended as part of a healthy diet, but evidence of the impact of individual species and biological concentrations on cognitive function is limited,” the researchers wrote. The researchers measured levels of the omega-3s ALA, EPA, DHA and DPA. And they looked at a host of omega-6 fatty acids, including ARA (arachidonic acid) and LA (linolenic acid).
Large study size
The researchers noted that Hispanics in general, and those from the Caribbean in particular, are at greater risk of cognitive impairment. Participants in the study, who self identified as Puerto Rican, were recruited in the 2004-2009 time frame. After exclusionary criteria were applied, 1,404 participants began the study and 1,197 returned for a 2-year follow up, with smaller (but still significant) numbers of participants completing all of the tests.
Erythrocyte and dietary PUFA composition were ascertained at baseline and associated with 2-year scores on the Mini-Mental State Exam (MMSE) (1032 participants) and cognitive domain patterns derived from a battery of tests ( 865 participants), as well as with incidence of cognitive impairment.
The MMSE is a widely used test of cognitive function among the elderly; it includes tests of orientation, attention, memory, language and visual-spatial skills. Poor scores indicating mental impairment are tagged to education level; a score of 22 or lower for individuals with a 7th grade education raises a red flag, whereas for an individual who has completed at least some college courses, that score is 26.
In addition to the MMSE, the cognitive tests that were administered included Word List Learning, Digit Span Forward and Backward, the Stroop Test, Verbal Fluency, Clock Drawing, and Figure Copying.
Dietary intakes were obtained for the prior 12 months by questionnaires administered by trained interviewers. The researchers said they employed a questionnaire that had been validated for use with a Puerto Rican population.
Higher omega-3s associated with better cognitive performance
The researchers found that higher levels of EPA, DHA and DPA were associated with better executive function. But they found no correlation with higher levels of those fatty acids and scores on the MMSE.
They also found that higher levels of omega-6s were associated with poorer executive function as well as lower scores on the MMSE. More ARA in the blood—though, curiously, not in the diet—was associated with outright cognitive impairment.
The researchers said that a longer study period might have helped establish a better correlation with omega-3 levels and cognitive performance.
“A longer study period would have allowed for greater decline in cognitive function, improving our ability to detect a FA connection,” they wrote. They also noted that the baseline omega-3s levels of the study population was low to begin with, meaning that many individuals may have been below therapeutic thresholds.
More to learn from population studies
Dr Harris of OmegaQuant said the study adds to the wide variety of population-based knowledge on omega-3s.
“I think this is a piece of the puzzle,” he said. “It supports the relationship of higher omega-3 levels and better cognitive performance. But it doesn’t necessarily help prove the point that giving more omega-3s results in these outcomes.”
Harris said that while population based studies are old hat in the omega-3s game, there is still much more to be done.
“We are working on a study now comparing omega-3 levels across as many as 10 populations. As I recall from doing the analytical work on this study, the omega-3 levels of the Puerto Ricans living in Boston were lower than was observed in the Framingham Study, which was done in the same city,” he said.
As far as the negative associations in the study are concerned, Harris said the results fit into the ‘ARA promotes inflammation, and therefore is bad’ narrative. But he said lipid chemistry in the body doesn’t lend itself to simplistic a-b = c type calculations.
“High ARA levels means pro inflammatory. That’s the dogma. But we have also seen examples where that is not the case. It turns out that it is hard to move the ARA level in an individual. It’s still an area of research and controversy,” he said.
2018 Sep 6;10(9). pii: E1253. doi: 10.3390/nu10091253.
“Prospective Associations of Erythrocyte Composition and Dietary Intake of n-3 and n-6 PUFA with Measures of Cognitive Function.”
Authors: Bigornia SJ, Scott TM, Harris WS, Tucker KL
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