Higher Serum DHA Linked to Less Amyloid, Better Memory

Megan Brooks

August 17, 2016

New research supports neuroprotectant effects of docosahexaenoic acid (DHA) in the aging brain.

In a small cross-sectional study of cognitively healthy older adults, higher serum DHA levels were associated with less cerebral amyloidosis, better memory scores, and less regional brain atrophy.

"The interesting finding was the association of low serum DHA levels with cerebral amyloidosis (amyloid plaques) in older adults without evidence of dementia," Hussein N. Yassine, MD, Department of Medicine, University of Southern California, Los Angeles, told Medscape Medical News. "This association was predominantly driven by persons at the lowest quartile of serum DHA levels who likely have limited intake of seafood."

"This study adds to the existing evidence on the benefit of seafood consumption on [Alzheimer's disease] AD risk factors," Dr Yassine added.

The study was published online August 8 in JAMA Neurology.

In a linked editorial, Joseph F. Quinn, MD, Department of Neurology, Oregon Health and Science University, Portland, notes that DHA is "the most abundant polyunsaturated fatty acid in the brain, playing an important structural role in synapses while also modulating a number of signaling pathways.

"Brain DHA levels are also modulated by dietary intake, so it is plausible for dietary DHA to alter brain concentrations and affect downstream targets including brain pathology and function."

The Aging Brain Study

Dr Yassine and colleagues assessed serum DHA levels, measures of amyloid burden based on positron emission tomography with Pittsburgh compound B, brain volume, and neuropsychological test scores in 61 adults without dementia in the Aging Brain Study.

They found that serum DHA levels (percentage of total fatty acids) were 23% lower in those with cerebral amyloidosis relative to those without (0.97 vs 1.25; P = .007).

Serum DHA levels were inversely correlated with brain amyloid load (r = –0.32; P = .01), independent of age, sex, years of education, and apolipoprotein E genotype.

They also noted a positive correlation between serum DHA levels and brain volume in several subregions affected by AD, in particular the left subiculum (r = 0.38; P = .005) and the left entorhinal volumes (r = 0.51; P = .001).

Clinically, there was a significant association between serum DHA levels and nonverbal memory (r = 0.28; P = .03). This association persisted after adjustment for age (P = .02) but not after adjustment for apolipoprotein E genotype (P = .10). Serum DHA levels were not associated with measures of global cognition, executive function, or verbal memory scores.

"The main message for clinicians would be to inquire about seafood consumption in older adults as part of understanding the risk for cognitive decline and Alzheimer's disease," Dr Yassine told Medscape Medical News.

"On the basis of this cross-sectional study alone, we cannot recommend DHA supplementation. We hope our study will spark interest in conducting prevention studies to address whether DHA supplementation in nondemented individuals with limited seafood consumption can prevent or slow the development of Alzheimer's disease," Dr Yassine added.

Adhere to Fish Recommendations

In his editorial, Dr Quinn also cautions against invoking cause and effect from a small cross-sectional study, offering that plasma DHA may be a "nonspecific marker of healthy lifestyle rather than a 'driver' of the effect on cerebral amyloid."

At present, the potential of DHA supplementation as an antiamyloid strategy for the prevention of AD remains unclear, Dr Quinn notes.

For now, maybe the "best advice is to adhere to the recommendations from the Centers for Disease Control and Prevention and from the American Heart Association and American Stroke Association, each of which recommend eating fish 2 to 3 times per week, primarily for vascular health," he writes.

"Several lines of evidence now support the view that reducing vascular risk may reduce not only cerebrovascular disease but also cerebral amyloid deposition. This perspective may serve as a guide for counseling patients at risk for AD and for interpreting the relationship between DHA and cerebral amyloid that has been brought to our attention by Yassine et al," Dr Quinn concludes.

Funding for the study was provided by the National Institutes of Health, the LK Whittier Foundation, and Huntington Medical Research Institutes. One author disclosed serving as a consultant to Genentech, Novartis, Banner Alzheimer Institute, and Bioclinica.

JAMA Neurol. Published online August 8, 2016. Abstract Editorial

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