ReviewThe Effect of Omega-3 on Circulating Adiponectin in Adults With Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Introduction
Type 2 diabetes mellitus is 1 of the most prevalent noncommunicable chronic diseases worldwide (1). Type 2 diabetes is strongly associated with obesity because the excess of intra-abdominal fat is associated with insulin resistance, increased levels of inflammatory cytokines and decreased levels of adiponectin (2). Adiponectin, a protein secreted by adipose tissue, has been postulated to play an important role in the modulation of glucose and lipid metabolism as well as insulin-sensitive tissues in both humans and animals (1). In humans, plasma levels of adiponectin are significantly lower in insulin-resistant states, including type 2 diabetes 3, 4. Adiponectin prevents the development of type 2 diabetes and atherosclerosis in animal models (5). In the same vein, experimental studies in animals have also consistently found that n-3 polyunsaturated fatty acids intake increases circulating levels of adiponectin 6, 7. However, whether the consumption of n-3 polyunsaturated fatty acids affects circulating adiponectin in type 2 diabetes mellitus has not been established. To address this gap in knowledge, we performed a systematic review and meta-analysis based on the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. PICO (P, patient, problem or population; I, intervention; C, comparison, control or comparator; O, outcome). The PICOs were defined as follows: type 2 diabetes mellitus (participants), omega-3 intake (intervention), compared to placebo (comparison), adiponectin concentration (outcome) and randomized placebo-controlled clinical trials (study design). This study is registered on PROSPERO, #CRD42016038573.
Section snippets
Search strategy
The electronic databases PubMed, Scopus and Web of Science were searched for randomized, placebo-controlled trials investigating the effect of omega-3 intake on circulating adiponectin in people with type 2 diabetes. The trials were published between 1955 and May 2016 in English. We used the following search terms: EPA, DHA, docosahexaenoic acid, eicosapentanoic acid, fish oil, alpha-linolenic acid, omega-3, n3, diabetes, metabolic disease, glucose metabolism disorders, diabetes mellitus,
Flow of included studies
Of 294 identified reports, 283 were excluded based on the initial review (Figure 1). The full-text articles of the remaining 11 reports were retrieved and reviewed. Of these, 3 were excluded because they lacked placebo control 9, 10, 11. One additional study nominally met inclusion criteria but did not contain sufficient data for quantitative analysis (12), which could not be obtained despite the authors' repeated requests and was, therefore, excluded. After the final exclusions, 7 studies met
Discussion
This systematic review and meta-analysis suggests that omega-3 (food or supplement) increases circulating adiponectin in patients with type 2 diabetes. Based on our knowledge, this is the first demonstration that omega-3 influences circulating adiponectin in patients with type 2 diabetes. In 2013, a meta-analysis was conducted to examine the effect of fish oil on circulating adiponectin (20). In this meta-analysis of intervention studies, in only 1 of the studies included in the current
Conclusions
In conclusion, this systematic review and meta-analysis of randomized, placebo-controlled clinical trials suggests that omega-3 in patients with type 2 diabetes increases circulating adiponectin. These findings support the potential beneficial effects of omega-3 in patients with type 2 diabetes on pathways related to adiponectin metabolism.
Author Disclosures
Conflicts of interest: None.
Author Contributions
MB, AR, AM and FSH made substantial contributions to the conception and study design; MB and AR were involved in data extraction; MB, AR and AM were involved in statistical analysis and the drafting of the manuscript; FSH critically revised the manuscript. All authors read and approved the final manuscript.
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