Results from a 20-year study indicate that higher levels of cardiorespiratory fitness reduce the risk for developing prediabetes or type 2 diabetes, even after accounting for changes in BMI.1
Previous data show that people who maintain or increase their cardiorespiratory fitness through adulthood have a lower risk for diabetes, abnormal metabolic measures, cardiovascular disease, and cardiovascular mortality, as compared with those whose fitness declines. These studies, however, have several significant limitations.
“Much, but not all, of the current literature on cardiorespiratory fitness change has been focused on men, with either varying duration between cardiorespiratory fitness assessments, or a limited period (5-7 years) between cardiorespiratory fitness assessments,” noted the researchers.
The current study, which was published in Diabetologia, extends a previous analysis of data from the Coronary Artery Risk Development in Young Adults (CARDIA) study. CARDIA objectively documented fitness using treadmill exercise testing to measure cardiorespiratory fitness at baseline (ages 18 to 30; year 0), in early adulthood (ages 25 to 37; year 7), and at middle age (ages 38 to 50; year 20). Documentation of incident prediabetes and diabetes was tracked over 25 years.
At baseline, CARDIA included 5115 black and white men and women from 4 communities in the United States (Birmingham, Alabama; Chicago, Illinois; Minneapolis, Minnesota; and Oakland, California) who were recruited and examined during 1985 to 1986. After exclusion of participants who did not have baseline treadmill results, a diabetes assessment at baseline, a diagnosis of prediabetes or diabetes at baseline, or at least 1 follow-up visit documenting prediabetes or diabetes status, as well as those lost to follow-up, 4373 participants were included in this analysis.
By year 25, 1941 participants (44.5%) developed prediabetes and 505 (11.5%) developed diabetes.1
While accounting for the time-varying aspect of BMI, the researchers found that higher cardiorespiratory fitness was associated with lower risk for developing prediabetes and diabetes (difference of 1 metabolic equivalent [MET] increment, hazard ratio [HR]=0.99898; P<.01).1 This finding persisted after adjustment for baseline lifestyle factors, including smoking, energy intake, alcohol intake, and education, as well as systolic blood pressure, blood pressure medications, and LDL and HDL cholesterol levels (difference of 1 MET increment, HR=0.99872; P<.01).1
These results suggest that an 8% to 11% higher fitness level reduced the risk for prediabetes or diabetes by 0.1% when using treadmill exercise testing as a measure of cardiorespiratory fitness. The researchers noted that the amount of physical activity required to increase an individual’s fitness by 1 MET depends on multiple factors, such as age, health and baseline activity, as well as the duration, intensity, and form of exercise. For reference, another study published in the Journal of Applied Physiology indicated that achieving a higher level of fitness required either vigorous physical activity for 30 minutes daily 5 days per week or moderate physical activity for 40 minutes daily 5 days per week.2
“This study is clinically relevant as it provides evidence to support commonly accepted dogma that fitness is beneficial in reducing the risk for prediabetes/diabetes,” the researchers concluded. “As this benefit remained significant even when adjusting for BMI, exercise programs remain critically important for reducing the development of prediabetes and diabetes.”
The study had some limitations, the researchers noted, including the fact that cardiorespiratory fitness is not equivalent to physical activity and has a significant genetic component, among others.