Objective: The relation between body weight and mortality in type II diabetic patients has not been fully elucidated. The aim of the present study was to evaluate the impact of body weight on mortality in a well-characterized type II diabetic cohort.
Research design and methods: We examined a cohort of 3398 type II diabetic patients, alive on December 1986 and followed up for 10 years, to assess mortality and its causes and to investigate the relationship between body mass index (BMI) and mortality from all and specific causes. For this purpose, survival in the different quartiles of BMI was evaluated by a Cox model, controlling for sex, age, treatment, smoking, duration of diabetes, hypertension, and fasting plasma glucose. The Cox model was applied either excluding (model 1) or including (model 2) the last three variables.
Results: During the 10 ys of follow-up, 1212 deaths (639 women, 573 men) occurred in the cohort under study. Since the interaction between BMI and age was statistically significant (P = 0.002), survival was studied separately in people aged <65 and > or =65 y (median age of the cohort = 65.9 y). Under 65 y, a significantly higher all-cause mortality was observed in obese patients, that is, in the IV quartile (BMI> or =30.9 kg/m(2); RR = 1.74; CI 95% = 1.26-2.40), in model 1. The inclusion of hypertension, duration of diabetes, and fasting plasma glucose in the model (model 2) slightly decreased the relative risk (RR = 1.52; CI 95% = 1.10-2.11). After 65 y, higher body weight was associated with a better outcome, especially in patients belonging to the IV quartile of BMI (RR = 0.74; CI 95% = 0.62-0.90).
Conclusions: In older type II diabetic patients, a moderate excess weight predicts a better survival, while obesity is a negative prognostic factor in patients younger than 65 y. In the latter patients, the effect of obesity on mortality seems to be partly mediated by hypertension, duration of diabetes, and fasting plasma glucose.