Age-Related Trends in the Prevalence of Type 2 Diabetes among Japanese and White and Black American Adults

Aim: To compare the prevalence of poor glycemic control in probability samples of Japanese and American adults, and to determine the association with their somatic phenotypes.

Material and methods: Blood samples and anthropometric measures were obtained from 382 Japanese, 32-79 years of age, randomly selected to reflect the 23 wards of Tokyo. HA1c values were compared to 1215 Americans, 35-86 years of age, from a national study across the 48 continental states, along with an over-sampling of African-Americans from one city (www.midus.wisc.edu). Body Mass Index (BMI) and Waist-hip ratio (WHR) were also assessed.

Results: Many Japanese now have high HA1c approaching Caucasian-American levels, although elevated HA1c (>6.5%, 48 mmol/mol) is not nearly as prevalent as among African-Americans. Significant age-related trends were evident in both countries, with poor glycemic control occurring at younger ages in males and rarely found until old age in Japanese women. Japanese had higher HA1c levels at BMIs of 23-25, in contrast to Americans with Type 2 diabetes who more typically had a BMI over 30. Central adiposity predicted HA1c levels better than BMI, a relationship also apparent at a smaller WHR in Japan.

Conclusion: The prevalence of high HA1c in Tokyo almost rivals white Americans, but those statistics are dwarfed by the 37% of Afr-Amer adults identified with Type 2 diabetes. Elevated HA1c was more common in men, reflecting central adiposity, but poor glycemic control was also widespread among overweight Afr-Amer women. Type 2 diabetes was higher among older Japanese, when more women succumb. Overall, the findings highlight the societal and clinical challenges posed by demographic trends in both countries.