Erythrocyte membrane n3 fatty acid levels and carotid atherosclerosis in Chinese men and women

Objective Prospective studies have supported the beneficial effects of n 3 fatty acid consumption on cardiac deaths, but limited data focused on atherosclerosis. We investigated the associations between n 3 fatty acids in erythrocytes and atherosclerosis in middle aged and older Chinese. Methods 847 subjects (285 men and 562 women), aged 40 to 65 years, from Guangzhou, China were included in this community based cross sectional study between December 2005 and January 2008. The levels of a linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in erythrocytes were measured by gas chromatography. Carotid ultrasound examination was conducted to obtain intimae media thickness of the common carotid artery and the carotid bifurcation. Dietary data and other covariates were collected using interviewer-administered questionnaires. Results After adjustment for age, sex, and other confounders, negative dose response associations between the contents of individual n 3 polyunsaturated fatty acids in the erythrocyte membrane and the prevalence of carotid artery wall thickening and plaque were observed. A comparison in the highest and lowest tertiles gave odds ratios (95 per cent  confidence interval) for thickening in the walls of the common carotid artery of 0.58 for DHA, and 0.39  for ALA. However, EPA was not significantly associated with carotid atherosclerosis. Similar results were found for thickening at the carotid bifurcation and the occurrence of carotid artery plaque.
Conclusions Higher levels of DHA and ALA in the erythrocyte membrane were significantly associated with a lower burden of subclinical atherosclerosis. (Authors abstrsact)

The levels of fish consumption in Mainland Chinese are far lower than those of the Japanese and Europeans, and the median consumption of fish and EPA and DHA was reported to be approximately 32 g per day and 70 mg per day in men and women in Shanghai, respectively. ALA rich in oils of rapeseed, walnuts, soybeans and other plant oils, are common in the habitual Chinese diet. Although most studies have focused on the effects of EPA and DHA, but not those of ALA, emerging evidence has suggested that ALA might also be beneficial for the prevention of atherosclerosis. The intimae media thickness (IMT) of the carotid artery is a well-established surrogate measure for the detection of early atherosclerosis. The present study aimed to investigate whether total and various types of n3 fatty acids (ALA, EPA and DHA) in the erythrocyte membrane (biomarkers as the internal dose of dietary intakes) were inversely associated with the prevalence of carotid atherosclerosis among middle aged and older Chinese. In this community based study, higher levels of ALA, and DHA in the erythrocyte membrane were significantly and dose dependently associated with a lower burden of carotid atherosclerosis in apparently healthy men and women with a low habitual n minus 3 fatty acid intake.

No significant associations between EPA and the extent of carotid atherosclerosis were observed.   In the current analysis, ALA in erythrocyte membrane was strongly and inversely associated with carotid wall thickening and carotid plaque after adjustment for potential confounders.  The health benefit of ALA has not been consistently observed in previous studies. Several reasons might contribute to the study heterogeneity: possibly a small effect size of ALA on CVD risks; varied intake in different study populations; ALA effects might be modified by the intake of n6 fatty acids or other n3 long chain fatty acids in different populations.  Previous study showed that the benefits of ALA on CVD events were seen when EPA and DHA intake was very low. Further well-designed RCTs are needed to verify the ALA effect on cardiovascular health.  n 3 fatty acids might prevent atherosclerosis by reducing the quotient oxLDL to LDL , decreasing inflammation, improving blood lipids or endothelial function. The findings showed that n3 fatty acids estimated by RBC biomarkers but not dietary intakes by FFQ were associated with a decreased prevalence of atherosclerosis. The use of objective RBC biomarkers might provide much more accurate and precise estimates of the internal dose of n 3 fatty acids than those of dietary assessments by FFQ, and would thus improve the validity of the associations between n 3 fatty acids and carotid atherosclerosis in this study. In conclusion, this study indicated that the levels of ALA and DHA in the erythrocyte membrane were significantly and inversely associated with the prevalence of carotid atherosclerosis in a middle aged and older Chinese population with a low intake of n3 fatty acids. (Editors comments)