Plasma fatty acids and lipids in two separate, but genetically comparable, Icelandic populations.

Levels of serum lipids and lipoproteins, and the fatty acid composition of plasma phospholipids, were measured in two genetically comparable, but widely separated, populations. The 1975 mortality rates for ischemic heart disease were significantly higher in one of these populations, the Manitoban residents of pure Icelandic descent, than in the other, a rural population from Northeastern Iceland. Two study populations, Icelanders and Icelandic-Canadians, were drawn from these larger populations. The study populations were matched for age and sex and divided into three age groups, 20-39, 40-59, and 60-69 years. In comparison to the Icelandic-Canadians, the Icelanders exhibited significantly higher levels of total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol, but lower triglyceride levels. Their plasma phospholipids contained significantly lower levels of saturated fatty acids (SFA), monounsaturated fatty acids, and n-6 polyunsaturated fatty acids (PUFA); but their n-3 PUFA levels were three times as high. It was additionally found that fatty acid composition of plasma phospholipids differed among Icelanders of different ages. SFA levels were significantly lower, and n-6 PUFA levels significantly higher, in the 20-39 year group than in the 60-69 year group, possibly due to different dietary fat consumption patterns between generations. No corresponding age-related difference in the fatty acid composition of plasma phospholipids was found in the Icelandic-Canadian study population. As the Icelandic and Icelandic-Canadian groups are assumed to be genetically similar, the biochemical differences between them are evidently due to environmental, probably dietary, differences. The findings indicate that n-3 PUFA may be cardioprotective in the context of an otherwise atherogenic diet.