Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 348

In 1972, Bang and Dyerberg reported that the low prevalence of coronary heart disease in the Greenland Eskimos was attributable to diet.⁵¹ They went on to discover that that the plasma of Greenland Eskimos was higher in eicosapentaenoic acid (EPA) (enriched in marine diet) and lower in arachidonic acid than that of Eskimos living in Denmark⁵² and that EPA had anti‐atherogenic properties, further explaining the differences in CAD prevalence among the populations. General recommended intake of the essential omega‐3 fatty acid alpha‐linolenic acid (ALA), the substrate for EPA, is 1.1 g for women and 1.6 g for men age 51 and older. Although there is no consensus on the intake of EPA and docosahexaenoic acid (DHA) in the US, Dieticians of Canada (2013) recommend intake of at least two servings of fish per week, thus providing approximately 0.3–0.45 g of EPA and DHA per day. This is an area for future work, particularly in the elderly, where elongation of ALA to these EPA and DHA polyunsaturated fatty acids (PUFAs) are limited (4% at best). Sources of ALA are plant‐based (flax and chia seeds, walnuts, and echium seed oil), and EPA and DHA are exclusively marine sourced (liver of lean white fish such as cod and halibut and the body of oily fish such as mackerel, menhaden, and salmon). These fatty acids are also abundant in the blubber of marine mammals such as seals and whales.⁵³

While DHA is the most abundant omega‐3 in the brain (~10,000 nmol/g of whole brain or 35% of grey matter), its precursor EPA concentrations are marginal in the CNS (<250 nmol/g).⁵⁴ However, in situ and in vivo models suggest that the brain’s demand for both EPA and DHA are similar, but EPA is rapidly metabolized and esterified to glia where it is concentrated more abundantly than DHA.^54–56 EPA and DHA are substrates for the synthesis of pro‐resolving lipid mediators that may offer benefit to the brain, bone, and muscles either directly or through vascular and anti‐inflammatory mechanisms.^57,58 Animal studies indicate that omega‐3 inhibits glial activation and tumour necrosis factor (TNF) alpha expression and optimises phospholipase A2 activity.⁵⁹ These findings have been confirmed in clinical trials where reductions in peripheral TNF‐alpha, increases in some indicators of white matter integrity,⁶⁰ and cerebral perfusion are seen with omega‐3 supplementation.⁶¹ Blood measurement (plasma and erythrocyte membrane concentrations) of the omega‐3 PUFA can provide a reliable indication of n‐3 PUFA status (EPA+DHA). Omega‐3 PUFA (EPA+DHA) >5% of total fatty acids or plasma EPA+DHA >110 ug/ml may offer neuroprotection in older adults^62,63