Heavy smoking raises risk for type 2 diabetes mellitus in obese men; but, light smoking reduces the risk in lean men: a follow-up study in Japan.
OBJECTIVE
To investigate interactive effects of cigarette smoking and body mass index (BMI, measured in kilograms per square meter) on the risk for type 2 diabetes mellitus (DM).


METHODS
We conducted a follow-up study in 16,829 apparently healthy men 30 to 59 years of age. At baseline, 23.1%, 24.6%, 24.0%, and 28.4% of the men were 'never' smokers, ex-smokers, light smokers (<or=20 cigarettes/d), and heavy smokers (>20 cigarettes/d), respectively. BMI was expediently categorized into quartiles (Q1: <21.3; Q2: 21.3-22.9; Q3: 23.0-24.7; and Q4: >24.7 kg/m2). Incident DM was identified by a fasting serum glucose level of 7.00 mmol/L or higher or the criterion 'under treatment for DM.' The risk ratio for incident DM, hazard ratio (HR) and the 95% confidence interval (CI), according to smoking and BMI, were estimated by using Cox proportional hazard models. Age, drinking, exercise, and education were computed as confounders.


RESULTS
During mean follow-up of 7.4 years, 869 men developed DM. In Q4 of BMI, heavy smoking raised the risk against 'never smoking' (multivariate-adjusted HR (95%CI): 1.37 [1.05-1.80]), but neither light smoking nor ex-smoking did. In Q1 of BMI, light and heavy smoking reduced the risk (multivariate-adjusted HR (95% CI): 0.45 (0.23-0.88) and 0.74 (0.41-1.33), respectively).


CONCLUSIONS
Smoking and BMI interactively influence risk for DM and the interaction is considerably complex. Heavy smoking moderately increases the risk for DM in obese men. But, light smoking reduces the risk in lean men.
Nagaya
Teruo
T
Department of Public Health, Nagoya City University Graduate School of Medical Sciences, Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan. nterubo@med.nagoya-cu.ac.jp
Yoshida
Hideyo
H
Takahashi
Hidekatsu
H
Kawai
Makoto
M
D000328:Adult; D015992:Body Mass Index; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology*; D005500:Follow-Up Studies; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D009765:Obesity; D016016:Proportional Hazards Models; D018570:Risk Assessment; D012907:Smoking / Q000453:epidemiology*; D013851:Thinness