By Will Boggs MD
NEW YORK – Higher serum docosahexaenoic acid (DHA) levels are associated with less cerebral amyloidosis, according to results from the Aging Brain Study.
"This study adds to the existing evidence on the benefit of seafood consumption on Alzheimer disease (AD) risk factors," Dr. Hussein N. Yassine from the University of Southern California, Los Angeles, told Reuters Health by email.
DHA accounts for 30% to 40% of fatty acids in cortical gray matter and is more concentrated at synapses. In preclinical studies, DHA has been shown to have neuroprotective qualities, including the prevention of amyloid plaque formation.
Dr. Yassine's team studied the possible association between serum DHA levels and cerebral amyloidosis, brain volumes, and cognitive measures among 61 Aging Brain Study participants without dementia who underwent amyloid PET imaging.
Serum DHA levels were 23% lower in participants with cerebral amyloidosis than in those without and were inversely correlated with brain amyloid load, independent of age, sex, apolipoprotein E (APOE) genotype, and years of education, the team reports in JAMA Neurology, online August 8.
"This association was predominantly driven by persons at the lowest quartile of serum DHA levels who likely have limited intake of seafood," Dr. Yassine said.
In fact, serum DHA (as a percentage of total fatty acids) and APOE group were the only independent predictors of cerebral amyloidosis.
Serum DHA levels directly correlated with hippocampal and entorhinal brain volumes, two regions affected in AD, but not with primary motor cortex volumes, an area spared in AD.
There was also a significant association between serum DHA levels and nonverbal memory, but this association did not persist after adjusting for APOE genotype.
Serum DHA levels were not associated with measures of global cognition, executive functions, or verbal memory scores.
"On the basis of this cross-sectional study alone, we cannot recommend DHA supplementation," Dr. Yassine concluded. "We hope our study will spark interest in conducting prevention studies to address whether DHA supplementation in non-demented individuals with limited seafood consumption can prevent or slow the development of Alzheimer's disease."
"It is dangerous to invoke cause and effect from a small cross-sectional study, and it may be that plasma DHA is a nonspecific marker of healthy lifestyle rather than a 'driver' of the effect on cerebral amyloid," Dr. Joseph F. Quinn from Oregon Health and Science University in Portland writes in a related editorial. "On the other hand, the hypothesis that DHA exerts antiamyloid effects is testable: might DHA supplementation be a viable option as an antiamyloid strategy for the prevention of AD?"
"That question has been asked but has not been completely answered," he says. "Two large trials (n=302 and n=807, respectively) have failed to show a cognitive effect of DHA supplementation in healthy individuals, in part because the placebo group failed to decline over time as predicted."
"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," Dr. Quinn concludes.
JAMA Neurol 2016.
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