Fifteen studies were included in the review: 10 cohort studies; one case-cohort study; and four nested case-control studies. Follow-up ranged from one to 18 years.
Higher adiponectin levels were associated with a lower risk of type 2 diabetes. The RR for type 2 diabetes was 0.72 (95% CI: 0.67, 0.78, p < 0.001, 13 studies, n = 14,598) per 1-log μg/mL increment in adiponectin levels. Absolute risk difference was 3.9 per 1,000 person-years per 1 log μg/mL for elderly white and black individuals and 7.5 per 1,000 person-years per 1 log μg/mL for Japanese Americans. For individuals with impaired glucose tolerance the absolute risk difference was 30.8 per 1,000 person years per 1 log μg/mL . There was evidence of statistically significant heterogeneity (I2=43%, Q = 22.9, p = 0.04). The sensitivity analyses did not significantly affect the results. Analysis without log transformation gave a pooled RR of type 2 diabetes per 5 μg/mL increment in adiponectin levels of 0.74 (95% CI: 0.68, 0.80, 12 studies, n = 12,802) with evidence of statistically significant heterogeneity (I2 = 59%, p = 0.004). Results of other adjusted analyses were also reported.
There was no evidence of publication bias.