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In the news: Omega-3s & Cognitive Decline; Diet and Diabetic Retinopathy

n-3s Improve Measures of Cognitive Function

Cognitive impairment is prevalent among the elderly, and the omega-3 (n-3) fatty acids EPA and DHA may have a protective role in age-related cognitive decline.

The results of previous clinical trials investigating supplemental EPA/DHA in healthy older adults, in mild cognitive impairment (MCI), and in Alzheimer’s, suggest that those with MCI are more likely to respond. MCI, which is associated with a 10-fold increased risk of developing dementia, has become an important stage for early intervention.

Against this backdrop, university researchers in China conducted a 6-month, randomized controlled trial (1) in 86 older patients (mean age 71 years) with MCI to examine the effects of fish oil on cognitive function assessed by Basic Cognitive Aptitude Tests (BCAT). Participants received fish oil (daily dose of 720 mg EPA, 480 mg DHA) or placebo (olive oil).

Compared to controls, changes from baseline were significantly improved for the primary outcome measures of total BCAT scores, perceptual speed, space imagery efficiency, and working memory in the fish oil-supplemented group (all p < 0.01). Working memory, the ability to access information required for ongoing cognitive processes, is thought to underpin learning. There was no difference between groups for mental arithmetic efficiency or recognition memory. Subgroup analysis by sex showed that the cognitive improvements were more pronounced in men than women.

Since inflammation is a characteristic of many neuro-degenerative diseases, including Alzheimer’s, it’s hypothesized that early management of inflammation could prevent the cognitive decline of MCI.

Many studies have shown that n-3 supplementation can reduce plasma levels of cytokines IL-6, IL-10, TNF-α, and secretory phospholipase A2 (sPLA2) in humans, to achieve anti-inflammatory effects.

The researchers also measured these inflammatory markers as part of this study, finding a significant decrease in IL-6, TNF-α, and sPLA2 in the group receiving supplemental fish oil. No significant changes in these markers were noted in the placebo group.

While the sample size was relatively small in this study, the results suggest that n-3 fatty acids may improve some aspects of cognitive function in MCI, and they add to the overall body of evidence evaluating n-3 fats in this condition. Larger studies of longer duration are needed.

Diet & Diabetic Retinopathy: Systematic Review

Evidence linking dietary intake with diabetic retinopathy (DR) is growing, but still unclear. Australian researchers conducted a systematic review of the literature, with 31 studies (2) (3 interventional, 28 observational) meeting the criteria for inclusion.

Higher intakes of dietary fiber, oily fish, and greater adherence to a Mediterranean diet were found to be protective of DR. Higher total caloric intake was associated with a higher risk of DR. They found no association with DR for carbohydrate, vitamin D, and sodium intake, while associations with antioxidants, fatty acids, proteins and alcohol with DR were equivocal.
 
Comments: Several caveats apply when interpreting the results of this study. First, the included studies addressed intake from foods and dietary patterns, and did not include intake from supplementation.

Secondly, while total ’carb’ intake was not linked with DR risk, the studies reviewed did not take ‘carb’ quality (i.e. high vs. low glycemic index) into account. DR is a complication of diabetes, and abundant evidence associates lower glycemic index diets GI with a decreased risk for type 2 diabetes.

Finally, while the review found that oily fish intake was protective of DR, no link specifically between omega-3 intake and DR was found. However, the quality of the included studies varied, and a large study published in JAMA (2017) found that dietary intake of at least 500 mg/day of n-3 fatty acids was associated with a nearly 50% relative risk reduction for vision-threatening DR.

References

1. Bo Y, et al. n-3 polyunsaturated fatty acid supplementation improved the cognitive function in Chinese elderly with mild cognitive impairment: A double-blind, randomized controlled trial. Nutrients. 9(1) pii: E54, 2017.
2. Wong M, et al. Dietary intake and diabetic retinopathy: A systematic review. PLOS One 13(1):eO186582, 2018.