▎ WuXi AppTec content team editor
Studies have shown that obese people (defined as body mass index ≥30) have a 7-fold risk of developing type 2 diabetes as normal-weight adults. However, the extent to which systemic obesity and central obesity are associated with type 2 diabetes mellitus is not well summarized by the comprehensive epidemiological evidence.
Recently, a team from Tehran Medical University in Iran comprehensively reviewed weight, waist circumference and fat measurements and the relationship between different proportions of these measurements and the risk of type 2 diabetes, and the results were published in The BMJ.
Screenshot source: BMJ
A total of 216 studies, conducted in the general adult population, were included through a comprehensive search and screening, analyzing cohort studies in the general adult population that correlated systemic or central obesity and body fat content with the risk of type 2 diabetes and excluding patients with a history of diabetes at baseline. Of these, 190 (88%) were prospective studies and 26 (12%) were retrospective cohort studies, including data on nearly 26 million people, of whom more than 2.31 million had type 2 diabetes. All included studies were original studies published between 1991 and May 1, 2021.
Body mass index
Analysis of 182 cohort studies (covering approximately 5.856 million people, including more than 228,000 with type 2 diabetes) showed that for every 5 units increase in body mass index, the risk of developing type 2 diabetes increased by 72% (relative risk 1.72, 95% confidence interval 1.65-1.81, I2=99%).
waistline
Analysis of 78 cohort studies (covering approximately 21.46 million people, including more than 2 million people with type 2 diabetes) showed a 61% increase in the risk of type 2 diabetes for every 10 cm increase in waist circumference (relative risk 1.61, 95% confidence interval 1.52-1.70, I2=99%).
Waist-to-hip ratio
Analysis of 34 cohort studies (covering approximately 930,000 people (including 47,000 patients with type 2 diabetes) showed that for every 0.1 unit increase in the waist-to-hip ratio, the risk of developing type 2 diabetes increased by 63% (relative risk 1.63, 95% confidence interval 1.50-1.78, I2=99%).
Waist height ratio
Analysis of 25 cohort studies (covering approximately 210,000 people, including 12,000 people with type 2 diabetes) showed that for every 0.1 unit increase in waist circumference to height ratio, the risk of developing type 2 diabetes increased by 73% (relative risk 1.73, 95% confidence interval 1.51-1.98, I2=97%, n=25).
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Visceral fat index
Analysis of nine cohort studies showed that for every 1 unit increase in visceral fat index, the risk of developing type 2 diabetes increased by 42% (relative risk 1.42, 95% confidence interval 1.27 to 1.58, I2=84%).
Body fat percentage
An analysis of six cohort studies (covering 44,000 people, including 2,558 patients with type 2 diabetes) showed that a 10% increase in body fat percentage nearly doubled the risk of developing type 2 diabetes (relative risk was 2.05, 95% confidence interval 1.41 to 2.98, I2=91%).
Body Type Index
Analysis of five cohort studies (covering 480,000 people, including 26,000 people with type 2 diabetes) showed that for every 0.005 unit increase in body size index, the risk of developing type 2 diabetes increased by 9% (relative risk 1.09, 95% confidence interval 1.05-1.13, I2=71%).
Body obesity index
The Body Fat Index measures body fat based on height and hip circumference. Analysis of four cohorts (covering 60,790 participants, including 3,576 people with type 2 diabetes mellitus) showed a relative risk of 2.55 for every 10% increase in the body obesity index (95% confidence interval 1.59 to 4.10, I2=98%).
Hip circumference
Analysis of 14 cohort studies showed an 11% increase in hip circumference for every 10 cm increase in hip circumference.
brief summary
The analysis further revealed a strong linear positive correlation between body mass index and type 2 diabetes risk. Similar positive correlations were found in all regional and ethnic populations. The central obesity index was also positively correlated with the risk of type 2 diabetes, independent of the effects of systemic obesity. Although the number of studies was small, there was also a linear or monotonic positive correlation between total fat mass and visceral fat mass.
The findings suggest that the higher the body mass index, the higher the risk of developing type 2 diabetes. In addition to generalized obesity, a larger waist circumference is strongly linearly associated with the risk of type 2 diabetes.