Lifestyle risk factors and new-onset diabetes mellitus in older adults: the cardiovascular health study

Abstract

Background: The combined impact of lifestyle factors on incidence of diabetes mellitus later in life is not well established. The objective of this study was to determine how lifestyle factors, assessed in combination, relate to new-onset diabetes in a broad and relatively unselected population of older adults.

Methods: We prospectively examined associations of lifestyle factors, measured using repeated assessments later in life, with incident diabetes mellitus during a 10-year period (1989-1998) among 4883 men and women 65 years or older (mean [SD] age at baseline, 73 [6] years) enrolled in the Cardiovascular Health Study. Low-risk lifestyle groups were defined by physical activity level (leisure-time activity and walking pace) above the median; dietary score (higher fiber intake and polyunsaturated to saturated fat ratio, lower trans-fat intake and lower mean glycemic index) in the top 2 quintiles; never smoked or former smoker more than 20 years ago or for fewer than 5 pack-years; alcohol use (predominantly light or moderate); body mass index less than 25 (calculated as weight in kilograms divided by height in meters squared); and waist circumference of 88 cm for women or 92 cm for men. The main outcome measure was incident diabetes defined annually by new use of insulin or oral hypoglycemic medications. We also evaluated fasting and 2-hour postchallenge glucose levels.

Results: During 34,539 person-years, 337 new cases of drug-treated diabetes mellitus occurred (9.8 per 1000 person-years). After adjustment for age, sex, race, educational level, and annual income, each lifestyle factor was independently associated with incident diabetes. Overall, the rate of incident diabetes was 35% lower (relative risk, 0.65; 95% confidence interval, 0.59-0.71) for each 1 additional lifestyle factor in the low-risk group. Participants whose physical activity level and dietary, smoking, and alcohol habits were all in the low-risk group had an 82% lower incidence of diabetes (relative risk, 0.18; 95% confidence interval, 0.06-0.56) compared with all other participants. When absence of adiposity (either body mass index <25 or waist circumference < or =88/92 cm for women/men) was added to the other 4 low-risk lifestyle factors, incidence of diabetes was 89% lower (relative risk, 0.11; 95% confidence interval, 0.01-0.76). Overall, 9 of 10 new cases of diabetes appeared to be attributable to these 5 lifestyle factors. Associations were slightly attenuated, but still highly significant, for incident diabetes defined by medication use or glucose level.

Conclusion: Even later in life, combined lifestyle factors are associated with a markedly lower incidence of new-onset diabetes mellitus.

Figure 1

Relative risk (RR) of incident diabetes mellitus according to the number of low-risk lifestyle factors among 4883 older adults from 1989 to 1998. Diabetes was defined by new use of insulin or oral hypoglycemic medication (assessed annually). Low-risk lifestyle factors included physical activity above the median level, dietary score in the upper 2 quintiles, never smoking, alcohol use, body mass index less than 25 (calculated as weight in kilograms divided by height in meters squared), and waist circumference less than 88 cm for women or 92 cm for men. Adjusted for age (years), sex (male vs female), race (white vs nonwhite), educational level (high school), and annual income (<$25 000, $25 000–$49 999, and ≥$50 000). No cases of incident diabetes occurred among individuals with all 6 low-risk lifestyle factors.

Figure 2

Relative risk (RR) of incident diabetes mellitus determined by medication use or fasting glucose level criteria according to the number of low-risk lifestyle factors among 4526 older adults from 1989 to 1998. Diabetes was defined by new use of insulin or oral hypoglycemic medication (assessed annually) or a fasting glucose level of 126 mg/dL or higher (to convert to millimoles per liter, multiply by 0.0555) (assessed at years 3 and 7), excluding individuals who met these criteria at baseline. Low-risk lifestyle factors included physical activity above the median level, dietary score in the upper 2 quintiles, never smoking, alcohol use, body mass index less than 25 (calculated as weight in kilograms divided by height in meters squared), and waist circumference less than 88 cm for women or 92 cm for men. Adjusted for age (years), sex (male vs female), race (white vs nonwhite), educational level (high school), and annual income (<$25 000, $25 000–$49 999, and ≥$50 000). No cases of incident diabetes occurred among individuals with all 6 low-risk lifestyle factors.

Figure 3

Relative risk (RR) of incident diabetes mellitus determined by medication use, fasting glucose level, or 2-hour postchallenge glucose level criteria according to the number of low-risk lifestyle factors among 4155 older adults from 1989 to 1998. Diabetes was defined by new use of insulin or oral hypoglycemic medication (assessed annually), fasting glucose level of 126 mg/dL or higher (to convert to millimoles per liter, multiply by 0.0555) (assessed at years 3 and 7), or 2-hour postchallenge glucose of 200 mg/dL or higher (assessed at year 7), excluding individuals who met these criteria at baseline. Low-risk lifestyle factors included physical activity above the median level, dietary score in the upper 2 quintiles, never smoking, alcohol use, body mass index less than 25 (calculated as weight in kilograms divided by height in meters squared), and waist circumference less than 88 cm for women or 92 cm for men. Adjusted for age (years), sex (male vs female), race (white vs nonwhite), educational level (high school), and annual income (<$25 000, $25 000–$49 999, and ≥$50 000). Incident diabetes among individuals with all 6 low-risk lifestyle factors (n=2) was too infrequent to estimate risk reliably.