Physical inactivity predicts type 2 diabetes

Data from several prospective epidemiologic studies have shown an inverse association between physical activity and the incidence of type 2 diabetes [1-3]. Recently, Wei et al. extended these findings, which were based on self-reporting of physical activity and type 2 diabetes, by examining the relationship of objectively measured cardiorespiratory fitness to the incidence of impaired fasting glucose and type 2 diabetes [4]. This analysis included 8633 mostly white men with non-insulin-treated type 2 diabetes, who were followed for 6 years after baseline assessment of cardiorespiratory fitness by a maximal exercise test on a treadmill. Men in the low fitness group (the least fit 20% of the cohort) had a 1.9-fold risk for impaired fasting glucose and a 3.7-fold risk for diabetes compared to those in the high fitness group (the most fit 40% of the cohort) after adjusting for age, smoking, alcohol consumption and parental diabetes. After additional adjustment for body mass index, high-density lipoprotein (HDL) cholesterol and triglycerides and hypertension, the low fitness group still had a significantly increased risk of impaired fasting glucose (1.7-fold increase compared to the high fitness group) and diabetes (2.6-fold increase) (Fig. 4.4.1). These data support the hypothesis s

Age > 45 years

Age < 45 years

P=0.004

Parental diabetes

No parental diabetes

Impaired fasting glucose

Normal fasting glucose

Fig. 4.4.1 Incidence of type 2 diabetes per 1000 person-years by cardiorespiratory fitness levels according to age group (a), body mass index (BMI, b), history of parental diabetes (c), and impaired fasting glucose (d). White bars represent the low fitness group, light tinted bars represent the moderate fitness group, and dark tinted bars represent the high fitness group. Reproduced with permission from [4].

that physical inactivity plays a significant role in the pathogenesis of type 2 diabetes. Similar data have also recently been reported for women participating in the Nurses' Health Study. This prospective study included self-reported data on physical activity in women surveyed in the United States in 1986 with updates in 1988 and 1992 [5]. During 8 years of follow-up, 1419 cases of diabetes were documented. After adjusting for age, smoking, alcohol use, history of diabetes and hypertension, menopausal status and high cholesterol, the relative risks of developing diabetes across quintiles of increasing physical activity decreased from 1.0 to 0.54 [5]. After further adjustment for body mass index, the relative risk reduction was still significant and fell from 1.0 to 0.74 (lowest vs. highest quintile of physical activity). Importantly, equivalent energy expenditures from walking and vigorous activity resulted in comparable magnitudes of risk reduction [5]. These data suggested that in women also, greater physical activity level is associated with a sub stantial reduction in risk for type 2 diabetes and also suggested that physical activity of moderate intensity and duration is beneficial.

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