J Nutr., 2020., Mar 13. pii: nxaa039. doi: 10.1093/jn/nxaa039.

Erythrocyte Membrane Polyunsaturated Fatty Acids Are Associated with Incidence of Metabolic Syndrome in Middle-Aged and Elderly People-An 8.8-Year Prospective Study.

Ding D Li YH Xiao ML et al.

Abstract

BACKGROUND:  The total and specific types of polyunsaturated fatty acids (PUFAs) related to metabolic syndrome (MetS) remain inconsistent. OBJECTIVE:  We assessed the association of erythrocyte n-3 and n-6 PUFAs with MetS and the components of MetS in a cohort population. METHODS:  This prospective analysis included 2754 participants (aged 40-75 y) from the Guangzhou Nutrition and Health Study (2008-2019) in China. Erythrocyte PUFAs at baseline were measured using gas chromatography. MetS was assessed every 3 y according to the updated National Cholesterol Education Program Adult Treatment Panel III criteria. Multivariable Cox proportional hazard models were used to evaluate HRs and 95% CIs. RESULTS:  We identified 716 incident cases of MetS. The primary analyses showed that the HRs (95% CIs) of MetS (tertile 3 versus 1) were 0.67 (0.56, 0.80) for n-3 PUFAs and 0.70 (0.58, 0.85) for n-6 PUFAs (all Ps trend <0.001). The secondary outcomes showed that, higher erythrocyte very-long-chain (VLC) PUFAs [20:3n-3, docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), arachidonic acid (ARA), and 22:4n-6], but lower α-linolenic acid (ALA) and γ-linolenic acid (GLA), tended to be associated with lower incidences of MetS and its components; among individual MetS components, the associations of PUFAs were more pronounced for hypertriglyceridemia (HTG) and hypertension, followed by low high-density lipoproten (HDL) cholesterol. Significantly higher concentrations of n-3 PUFAs (total, DPA, and DHA) and n-6 PUFAs (total, ARA, and 22:4) were observed in participants with improved (versus progressed) status of MetS (all Ps trend ≤0.003). CONCLUSION: This study reveals that higher erythrocyte VLC n-3 and n-6 PUFAs, but lower 18-carbon PUFAs (ALA and GLA), are associated with lower risks of MetS components (HTG, hypertension, and low HDL cholesterol) and thereby lower MetS incidence in Chinese adults.

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Key Points

Previous observational studies have reported inconsistent results of the associations between dietary/circulating n–3 and n–6 PUFAs and metabolic syndrome (MetS) risk. This study aimed to assess the associations of erythrocyte n–3 and n–6 PUFAs with the incidence of MetS and the components of MetS in a population-based 8.8-y prospective study, in middle-aged and elderly Chinese people. The primary analyses found a significant decrease in the incidence of MetS among participants with higher erythrocyte total n–3 and total n–6 PUFAs. Further analyses showed that the beneficial association might be explained by the contribution of higher VLC PUFAs (20:3n–3, or EPA, DPA, DHA, ARA, or 22:4n–6) but lower concentrations of 18-carbon PUFAs (ALA or GLA), and the decreased incidences of HTG, hypertension, and low HDL cholesterol. The MetS status of participants during this 8.8-y period changed correspondingly.

Evidence regarding erythrocyte and intake of ALA is limited and inconsistent. The association of ALA and DPA, especially for long-term prospective studies with the risk of hypertension, requires further verification, as well as other CVD risk factors and more importantly, primary and secondary CVD outcomes. The study has several limitations. First, only erythrocyte membrane PUFAs were measured at baseline, which may not explain the integral exposure level of erythrocyte PUFAs of participants over 8.8 y. Second, participants with 1 or 2 MetS components at baseline tended to change to a healthy lifestyle. Therefore, the study may have underestimated the associations between PUFAs and MetS. In conclusion, this longitudinal study reveals that higher concentrations of n–3 and n–6 PUFAs (some VLC PUFAs: 20:3n–3, DPA, DHA, ARA, and 22:4n–6) were associated with a lower incidence of HTG, hypertension, and low HDL cholesterol and thereby benefited the incidence and improvement of MetS over 8.8 y. Future studies are necessary especially with regard to ALA which has shown positive benefits in pother studies when assessed within these parameters.