Prevalence and Associated Factor of Brown Adipose Tissue: Systematic Review and Meta-Analysis

BACKGROUND: Brown adipose tissue generates heat instead of storing energy. It is important in the regulation of body weight, and individual variation in adaptive thermogenesis can be attributed to variations in the amount or activity of BAT. OBJECTIVE: The objective of this study was to systematically review different articles to assess the prevalence of BAT and its associated factors and relation with obesity and diabetes mellitus. METHODS: A systematic review and meta-analysis were employed on published research works from different electronic databases using keywords. Cross-sectional studies and a few experimental studies were included for systematic review, and only studies done on human population were used for quantitative analysis. Twenty-two peer-reviewed papers were included in the systematic review, and eight papers were used for the meta-analysis for estimation of pooled prevalence of brown adipose tissue using selection criteria. RESULTS: The pooled prevalence of brown adipose tissue among adults was 6.97% (95% CI: 6.51–7.43), and it was 7.4% (95% CI 6.51-7.43) after sequential omission of a single study. The heterogeneity in estimating the pooled prevalence among the studies was statistically significant (Cochran Q test, P < 0.001, I(2) = 71.2%), and after sequential omission of a single study, it becomes Cochran Q test, P = 0.065, I(2) = 49.4%. The brown adipose tissue activity was significantly lower in overweight or obese subjects than in lean subjects. CONCLUSION: The percentage of adult individuals with brown adipose tissue was high, and its activity was reduced in obese individuals. Although it is reduced in amount, still it presents in obese individuals. So, activation of the brown adipose tissue in adult and older individuals should be a target for the treatment of obesity.