The clinical characteristics of the study participants are presented in Table 1 according to
smoking status. Current smokers were younger and had shorter duration of diabetes mellitus
compared with never smokers and past smokers. Duration of smoking was longer, whilst the
amounts of cigarette smoked (number of cigarettes per day and pack-years of cigarettes smoking)
were lower in current smokers than those in past smokers. Current smokers were more
likely to have alcohol drinking habits, depressive symptoms, and to be on insulin therapy and
were less likely to engage in regular exercise. Both patients with past and current smoking habits
tended to have higher waist circumference levels compared with never smokers.
Table 2 shows the age-adjusted mean values and partial regression coefficients (95% CIs) of
fasting plasma glucose (FPG) and HbA1c according to smoking status. The FPG levels did not
differ significantly among the groups, whereas HbA1c levels were higher in current smokers,
with a mean increase in the current smokers relative to that in the never smokers of 0.20%. Significant
elevation in HbA1c levels persisted after controlling for the confounding factors, namely,
age, duration of diabetes mellitus, total energy intake, current drinking habits, regular
exercise habits, depressive symptoms, use of oral hypoglycemic agents, use of insulin, and BMI.
Table 3 indicates the adjusted mean values and partial regression coefficients (95% CIs) of
FPG and HbA1c according to the amount of smoking. Values of FPG did not increase in association
with the amount of smoking. Conversely, HbA1c increased significantly with increases in
both number of cigarettes per day and pack-years of cigarette smoking compared with never
smokers, indicating a dose-response relationship (P for trend = 0.001 and