Association of obesity and risk of diabetic retinopathy in diabetes patients: A meta-analysis of prospective cohort studies

Methodological quality of the review: Medium confidence

Author: Zhu W, Wu Y, Meng YF, Xing Q, Tao JJ, Lu J.

Region: Europe, Asia, America.

Sector: Diabetic retinopathy

Sub-sector: Obesity, risk

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Diabetic retinopathy (DR), which was a common complication of diabetes, remained to be one of the leading preventable causes of visual impairment in the whole world.

Objectives:

To investigate the potential association between obesity and risk of DR.

Main findings:

In total, authors included 13 publications in the review. When the diabetes type was considered, both Type 2 Diabetes (T2DM) and mixed types were included in the analysis. The follow-up duration among all the studies ranged from one year to 20 years. The sites where the studies had been carried out were as follows: seven in Asia, five in Europe, and one in Americas. The Newcastle-Ottawa Scale (NOS) for all the included studies ranged from 5 to 8 and the average score was 7.15 stars. The rate of high-quality (>6 stars) were present in most included studies.

Authors report that the analyses of the 13 included studies showed that obesity was a risk factor for the incidence of DR (relative risk (RR), 1.20; 95% confidence interval (CI), 1.01–1.43; I2=59.6%). When only proliferative DR (PDR) was considered in the subgroup analyses, authors reported no significant association between obesity and risk of PDR was detected (RR, 1.15; 95%CI, 0.89–1.48; I2=32.5%). Authors detected significant harmful effect was detected in T2DM group (RR, 1.40; 95% CI, 1.05–1.87; I2=67.6%) but not mix group (RR, 1.04; 95% CI, 0.97–1.18; I2=0.00%). Subgroup analysis by study sites showed that the studies in Asia demonstrated significant relationship between obesity and DR risk (RR, 1.22; 95% CI, 1.04–1.44; I2=33.8%). However, authors state that the studies conducted in neither Europe nor America demonstrated statistically significant association.

Methodology: 

Inclusion criteria included: the association between obesity and DR was evaluated; a prospective cohort study design was adopted; the odds ratios (OR), relative risk (RR) with 95% confidence intervals (CI) or sufficient data to calculate them were reported. The exclusion criteria included: not cohort design was adopted; no available data in suitable format was reported.

PubMed, EMBASE, and web of science were searched by authors using selected key words regarding obesity and DR from inception to July 2016. No restrictions of language or publication data in literature search were applied. Besides, the reference lists of the selected articles were reviewed to identify additional eligible publications. When supplemental data were required, the contacts with corresponding authors of related studies were conducted if necessary.

Two authors independently extracted data of included studies. Considering the only prospective cohort studies were included in this study, authors used Newcastle-Ottawa Scale (NOS) to assess the quality of each included study.

A random-effects model was used for the quantitative synthesis. As all the included studies were prospective cohort study, RR values were used to evaluate the associations between obesity and the risk of DR. The test of heterogeneity in quantitative calculation across studies was carried out using both x² and I² test.  Authors conducted a subgroup analyses by stratifying study characteristics (such as DM type, study site, and adjusting status) were conducted to detect the sources of heterogeneity. Potential publication bias was assessed using the funnel plot analysis and Egger test.

Applicability/external validity:

Authors did not discuss the applicability and external validity of the results.

Geographic focus:

Authors reported that studies conducted in Asia showed significant relationship between obesity and DR risk (RR, 1.22; 95% CI, 1.04–1.44; I2=33.8%). However, the studies conducted in neither Europe nor America demonstrated statistically significant association.

Summary of quality assessment:

Overall, there is medium confidence in the conclusions about the effects of this study. The study authors used appropriate methods to extract data and assess the methodological quality of included studies. However, authors did not specify methods used to screen studies for inclusion. Therefore, we cannot be certain that selection bias was avoided in the review process. Authors appropriately report the limitations of included studies and do not draw strong policy conclusions.