Plasma omega-3 fatty acid response to a fish oil supplement in the healthy elderly.

Little information is available concerning whether incorporation of dietary omega-3 fatty acids into plasma lipids changes during healthy aging. Elderly (74 +/- 4 years old) and young (24 +/- 2 years old) adults were given a fish oil supplement for 3 weeks that provided 680 mg/day of docosahexaenoic acid and 320 mg/day of eicosapentaenoic acid, followed by a 2 week wash-out period. Compliance was monitored by spiking the capsules with carbon-13 glucose, the excretion of which was measured in breath CO2. In response to the supplement, plasma docosahexaenoic acid rose 42% more in the elderly but eicosapentaenoic responded similarly in both groups. Despite raising docosahexaenoic acid intake by five to tenfold, the supplement did not raise plasma free docosahexaenoic acid (% or mg/dL) in either group. We conclude that healthy aging is accompanied by subtle but significant changes in DHA incorporation into plasma lipids.

Unresolved issues in the link between docosahexaenoic acid and Alzheimer's disease.

Lower consumption of docosahexaenoic acid (DHA) is commonly but not always associated with higher risk of cognitive decline and diagnosis of Alzheimer's disease (AD). We review here the available data relating DHA to AD, with emphasis on DHA content of plasma and brain. Our assessment of this literature is that low DHA is not consistently observed in AD plasma or brain. However, in dietary and population studies, low DHA intake is usually associated with low plasma DHA. Therefore, at present, there is no clear explanation of why the usual low DHA intake-low plasma DHA relationship appears not to exist in AD. Adding to the confusion, preliminary and inconclusive reports tentatively suggest that dietary DHA could potentially reduce cognitive deterioration in AD. These inconsistencies between dietary DHA, plasma/tissue DHA, and possible DHA efficacy in AD may be more methodological than biological, and may arise in part because only one study to date has reported both DHA intake and plasma DHA values in the same AD patients. Studies reporting DHA intake and plasma levels while also undertaking a DHA intervention in AD would presumably help resolve these issues.

Omega-3 fatty acids, energy substrates, and brain function during aging.

The maintenance of optimal cognitive function is a central feature of healthy aging. Impairment in brain glucose uptake is common in aging associated cognitive deterioration, but little is known of how this problem arises or whether it can be corrected or bypassed. Several aspects of the challenge to providing the brain with an adequate supply of fuel during aging seem to relate to omega-3 fatty acids. For instance, low intake of omega-3 fatty acids, especially docosahexaenoic acid (DHA), is becoming increasingly associated with several forms of cognitive decline in the elderly, particularly Alzheimer's disease. Brain DHA level seems to be an important regulator of brain glucose uptake, possibly by affecting the activity of some but not all the glucose transporters. DHA synthesis from either alpha-linolenic acid (ALA) or eicosapentaenoic acid (EPA) is very low in humans begging the question of whether these DHA precursors are likely to be helpful in maintaining cognition during aging. We speculate that ALA and EPA may well have useful supporting roles in maintaining brain function during aging but not by their conversion to DHA. ALA is an efficient ketogenic fatty acid, while EPA promotes fatty acid oxidation. By helping to produce ketone bodies, the effects of ALA and EPA could well be useful in strategies intended to use ketones to bypass problems of impaired glucose access to the brain during aging. Hence, it may be time to consider whether the main omega-3 fatty acids have distinct but complementary roles in brain function.