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Can omega-3s prevent cognitive decline?

One of the most important issues with aging is decreased cognitive ability and eventually dementia. Since the brain has such high omega-3 content, many people supplement for prevention of these issues. This large, multi-year study put that practice to the test.

Study under review: Effect of Omega-3 Fatty Acids, Lutein/ Zeaxanthin, or Other Nutrient Supplementation on Cognitive Function - The AREDS2 Randomized Clinical Trial

Introduction

Dementia[1] affects 5% of adults in the US population aged 71-79 years, with a nearly 5-fold rise to 24% in those aged 80-89 years and a sharper rise still to 37% in those over 90-years. Additionally, about one-fifth[2] of all adults older than 71-years have some form of cognitive impairment without signs of dementia, and 10% of these people progress to dementia every year. In other words, a large segment of the elderly population suffers from cognitive impairment and either has dementia or is at a high risk of progressing to it. The brain is the most lipid-dense organ in the body, with 50-60%[3] of its total mass coming from phospholipids alone. Depending on the type of phospholipid, DHA concentrations range from 20-30%[4] of the total fat content and appear to increase with age[5], displacing omega-6 fatty acids. It has been argued[6] that humans are adapted to consume higher levels of DHA than we currently do, and that a displacement of DHA from the diet driven by excessive consumption of omega-6 fatty acids has resulted in the gradual depletion of DHA from membrane phospholipids and the subsequent rise of modern diseases. It has been proposed that DHA be considered at least “conditionally essential[7].”

Nine observational studies now support that increased dietary intake of fish[8] is associated with reduced risk for cognitive decline or dementia, and in the Framingham Heart Study the highest quartile of serum DHA concentrations was associated with a significant 47% reduction[9] in the risk of developing all-cause dementia. Additionally, DHA deficiency is linked to various maladies, including Alzheimer’s disease[10], schizophrenia[11], psychosis[11], and anxiety[12]. Some of the mechanisms by which DHA may help are shown in Figure 1. However, DHA is a polyunsaturated fatty acid that is by nature unstable and prone to oxidation. The oxidation of DHA is proposed[13] to be one of the factors leading to dysregulations seen in Alzheimer’s disease

Figure 1: How DHA may hypothetically help protect neurons

Lutein and zeaxanthin are carotenoids found in green leafy vegetables and brightly colored fruit. These plant pigments are the sole carotenoids in the retina, where they exist in ∼500-fold higher concentrations than in other body tissues and are believed to be protective[14] through their roles as blue-light filters and antioxidants. Lutein and zeaxanthin are also among the dominant carotenoids in human brain tissue, where they account for 66–77%[15] of total carotenoid concentration. It has been shown in animal models that lutein is able to protect[16] against DHA oxidation within the brain, and higher lutein status[17] is related to better cognitive performance in adults.

The current study was an attempt to evaluate how long-term supplementation with EPA and DHA and/or lutein and zeaxanthin affects aspects of cognition in an elderly population.

DHA is a primary fatty acid within the brain, and low levels have been linked to cognitive disorders. Lutein and zeaxanthin are the primary carotenoids within the brain that serve an important protective role against DHA oxidation. The current study sought to evaluate whether supplementation with these compounds would benefit cognition in the elderly.

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