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A Look at Trends in Diabetes Over Four Decades: The Framingham Heart Study

The prevalence of obesity, diabetes, and new onset diabetes continue to grow…

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Although there are more medications to treat diabetes and increasing survival among individuals with diabetes, recent studies still are showing a continual rise in diabetes throughout the United States. Research is now showing that pre-diabetes and diabetes prevalence have begun to parallel high rates of being overweight and obesity, which are also risk factors of diabetes. However some data suggests that obesity may have begun to level off over the last few years.

Researchers used the Framingham Heart Study, a community-based cohort study of cardiovascular disease and risk factors that has been in continuous operation since 1948 beginning with the Original Cohort. Recruitment of the Offspring Cohort began in 1971 and participants were then invited back for a second examination 8 years after the initial exam and subsequently every four years thereafter. The participants were between the ages of 40–55 years of age and free of diabetes at baseline (n = 4,795; mean age 45.3 years; 51.6% women) were followed for the development of diabetes during the 1970’s, 1980’s, 1990’s, and 2000’s. When the researchers looked at diabetes, it was defined as either fasting glucose ≥126 mg/dL or the use of antidiabetes medication at followup examination. Poisson regression was used to calculate any sex-specific diabetes incidence rates for a 47-year-old individual during each decade. Diabetes incidence rates were also calculated among obese, overweight, and normal weight individuals according to their BMI classification.

The results showed that the overall annualized rates of diabetes per 1,000 individuals were 3.0, 4.1, 6.0, and 5.5 in the 1970’s, 1980’s, 1990’s, and 2000’s, respectively. The age-adjusted relative risks of diabetes were 1.37 (95% CI 0.87–2.16; P = 0.17) in the 1980’s, 1.99 (95% CI 1.30–3.03; P < 0.01) in the 1990’s, and 1.81 (95% CI 1.16–2.82; P = 0.01) in the 2000’s, using the 1970s as the reference period. When compared with the 1990’s, the age adjusted relative risk of diabetes incidence in the 2000’s was 0.85 (95% CI 0.61–1.20; P = 0.36).

The researchers concluded that the risk of incident diabetes was higher in the 1990’s compared with the 1970’s. Diabetes incidence continued to be higher in the 2000’s when compared with the 1970’s. Researchers also noted that mean BMI increased with each decade, and diabetes incidence remains highest among obese individuals in their study.

Practice Pearls:

  • There was a reported shorter follow-up time in the 2000’s (6 years) compared with the other decades (8 years) which may have led to underestimation of the true diabetes incidence in the 2000’s. But a sensitivity analysis provided otherwise, results were similar.
  • Among class 1 obese (BMI 30 to <35 kg/m2), incidence rates were higher in the 1990s than in the 2000’s, but among class 2 obese (BMI ≥35 kg/m2) that trend was shown to be reversed.
  • The sample used in this study is primarily caucasian and not generalizable across other ethnicities.

Tobin M. Abraham, Karol M. Pencina, Michael J. Pencina. et al. "Trends in Diabetes Incidence: The Framingham Heart Study". Diabetes Care 2015;38:482–487.