Omega 3 Fatty Acids and Incident Type 2 Diabetes: A Systematic Review and Meta Anallysis

January 1, 2012 Human Health and Nutrition Data 0 Comments

Omega 3 Fatty Acids and Incident Type 2 Diabetes: A Systematic Review and Meta Anallysis

Year: 2012
Authors: Wu,, J.H. Micha, R. Imamura, F. Pan, A. Biggs, M.L. Ajaz, O. Djousse, L. Hu, F.B. et al
Publication Name: Br J. Nutr.
Publication Details: Volume 107; Suppl 2: Pages S214-27. doi: 10.1017/S0007114512001602.


The relationship between omega 3 polyunsaturated fatty acids from seafood (eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA) or plant (alpha linolenic acid, ALA) sources and risk of type 2 diabetes mellitus (DM) remains unclear. We systematically searched multiple literature databases through June 2011 to identify prospective studies examining relations of dietary n  3 PUFA, dietary fish and per or seafood, and circulating n3 PUFA biomarkers with incidence of DM. Data were independently extracted in duplicate by 2 investigators, including multivariate adjusted relative risk (RR) estimates and corresponding 95 per cent CIs. Generalized least squares trend estimation was used to assess dose response relationships, with pooled summary estimates calculated by both fixed effect and random effect models. From 288 identified abstracts, 16 studies met inclusion criteria, including 18 separate cohorts comprising 540,184 individuals and 25,670 cases of incident DM. Consumption of fish and or seafood was not significantly associated with DM nor were consumption of EPA plus DHA or circulating levels of EPA plus DHA biomarkers . Both dietary ALA and circulating ALA biomarker levels were associated with non significant trend towards lower risk of DM. Substantial heterogeneity (I2 to 80 per cent) was observed among studies of fish and seafood or EPA plus DHA and DM; moderate heterogeneity (greater than 55 per cent ) was seen for dietary and biomarker ALA and DM. In unadjusted meta regressions, study location (Asia vs. North America and Europe), mean BMI, and duration of follow up each modified the association between fish seafood and EPA plus DHA consumption and DM risk . We had limited statistical power to determine the independent effect of these sources of heterogeneity due to their high colinearity.  The overall pooled findings do not support either major harms or benefits of fish or seafood or EPA plus DHA on development of DM, and suggest that ALA may be associated with modestly lower risk.  Reasons for potential heterogeneity of effects, which could include true biologic heterogeneity, publication bias, or chance, deserve further investigation. (Authors abstract)
Type 2 diabetes mellitus (DM) accounts for 90 to 95 per cent  of all diabetes cases and has reached epidemic proportions globally, including in both developed and developing countries. As a major risk factor for coronary heart disease, stroke, blindness, kidney failure, and peripheral arterial disease, DM poses tremendous public health burdens. Based on animal experimental studies, n 3 PUFA improve several metabolic abnormalities underlying the development of DM. Such effects include insulin sensitizing effects via increased production and secretion of adipocytokines such as adiponectin and leptin; and potential prevention of insulin resistance via anti inflammatory effects mediated directly or through conversion to specialized proresolution mediators such as resolvins and protectins . Through modulation of transcription factors (e.g. sterol regulatory element binding protein 1c), n 3 PUFA could also enhance fatty acid oxidation and reduce de novo lipogenesis, effects which could reduce hepatic fat accumulation and preserve hepatic insulin sensitivity. Despite metabolic benefits in animal experiments, the impact of n 3 PUFA consumption on risk of DM in humans remain uncertain. This systematic review and meta analysis of prospective studies that assessed the relation of dietary n3 PUFA, fish and or seafood consumption, and biomarker levels of n  3 PUFA with the incidence of DM was conducted. The overall findings from this systematic review and meta analysis suggest that dietary EPA  plus DHA and fish seafood consumption do not have either major harmful or beneficial associations with the development of DM. Substantial heterogeneity in findings across studies was noted. Self reported estimates of fish or EPA plus DHA consumption could be partly related to the dietary assessment method, rather than to biologic effects of EPA plus DHA per se.
The findings suggest ALA could be protective, though this result was of borderline statistical significance. Few prospective studies of ALA and incident DM were found. But both estimated dietary consumption and circulating biomarkers of ALA were associated with a modest, non statistically significant trend towards lower risk of DM. These pooled estimates demonstrated relatively low heterogeneity between studies, suggesting more consistent findings among studies. In several animal models, dietary ALA or flaxseed oil improved insulin sensitivity and glycemic responses. Similarly, some, but not other, short term randomized clinical trials found that ALA or flaxseed oil moderately improved fasting plasma glucose and markers of insuin resistance in humans.  The results add to these limited but potentially important data that ALA may provide moderate protection against the development of DM. Because plant sources of n  3 PUFA are potentially more widely available on a global basis, our findings highlight the need for further clinical and observational investigation of these effects. Based on all available evidence from prospective studies, neither EPA plus DHA nor fish and  seafood intake have significant associations with risk of DM overall, while plant derived ALA is associated with non significant trends toward lower risk. (Editors comments)

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