Benefits of Continued Cardiorespiratory Fitness

Maintaining higher levels of cardiorespiratory fitness or increasing fitness up into middle age can significantly reduce the risk of the development of prediabetes and diabetes, according to a new study.

Researchers led by Lisa S. Chow, MD, of the Division of Diabetes, Endocrinology, and Metabolism at the University of Minnesota, Minneapolis, MN, conducted a prospective trial to investigate the association between cardiorespiratory fitness measured in young adulthood and middle age on the development of prediabetes (defined as impaired fasting glucose and/or impaired glucose tolerance) or diabetes by middle age.

They noted that a number of previous studies have shown people who maintain or increase their cardiorespiratory fitness through adulthood have a lower risk of developing diabetes, abnormal metabolic measures, cardiovascular disease, and cardiovascular mortality than those whose fitness declines. Previous studies were limited, however, because they included a largely male population, measured fitness over a limited duration, or prospectively measured fitness at varying intervals.

The study measured the impact of continued cardiorespiratory fitness in adulthood on the development of diabetes and prediabetes among 4373 black and white participants from the Coronary Artery Risk Development in Young Adults study over a period of 20 years.

The participants were recruited in 1985-1986 when they were aged 18 to 30 years. They completed baseline treadmill exercise testing to determine their cardiorespiratory fitness. Testing was repeated in year 7 of the study and again at year 20.

Prediabetes or diabetes status of the participants was determined at baseline and at years 7, 10, 15, 20, and 25. Prediabetes was defined as a fasting glucose of 5.6 to 6.9 mmol/L, a 2-hour oral glucose tolerance test of 7.8 to 11.1 mmol/L, or an HbA1c level of 5.7-6.4%. Diabetes was defined as a fasting glucose ≥7 mmol/L, use of medications for diabetes treatment, a 2-hour glucose tolerance test ≥11.1 mmol/L, or HbA1c ≥6.5%.

The results show that by year 25 nearly half (44.5%) of the participants had developed prediabetes and 11.5% had developed type 2 diabetes mellitus. Risk factors for developing prediabetes or diabetes by year 25 included older age, black race, and male gender. Also, participants with prediabetes or diabetes at this time were more likely to take blood-pressure medication, smoke, and have a higher body mass index (BMI).

Higher fitness was associated with lower risk for developing incident prediabetes/diabetes (difference of 1 MET: HR 0.99898), which persisted when adjusting for covariates, including age, race, sex, field center, and time-varying BMI at all time points.

Expanding the model to include smoking, energy intake, alcohol intake, education, systolic blood pressure, blood-pressure medication, and LDL and HDL cholesterol levels reduced the hazard ratio further to 0.99872 per MET increase.

In conclusion, the researchers stated that “examining participants who had fitness measured from young adulthood to middle age, we found that fitness was associated with lower risk for developing prediabetes/diabetes, even when adjusting for BMI over this time period. These findings emphasize the importance of fitness in reducing the health burden of prediabetes and diabetes.”

Reference: Chow LS, et al. Twenty year fitness trends in young adults and incidence of prediabetes and diabetes: the CARDIA study. Diabetologia. 2016 May 16. [Epub ahead of print]