The present study found that T2DM men had higher CIMT than T2DM women, especially in those with age ≥ 69 years. Age was the main risk factors of CIMT in both genders. However, the impact of ageing on CIMT progression only existed in male patients.
The gender difference in CIMT in T2DM patients was in line with other population researches. In a study of healthy Taiwan population, CIMT was significantly higher in men than in women (0.558 vs 0.527 mm, P = 0.012) . Kablak-Ziembicka et al confirmed this result in subjects without CVD (men vs women 1.05 vs 0.93 mm, P < 0.001) . CIMT in our study was higher than that in Taiwan healthy population, while was lower than that in population without CVD  or with normal glucose tolerance . This might be due to the differences in age, ethnicity and physical condition of study populations.
We found that gender difference in CIMT only existed in the group with age ≥ 69 years. This finding was consistent with the Tromsø study , which found that gender difference in CIMT was not significant in young population and gradually increased with age . Dalla Pozza et al reported that there CIMT was not different between male and female children with type 1 diabetes mellitus . However, contrary results were found in subjects without CVD risk factors studied by Sinning et al . In their study, gender difference in CIMT only exists in young population (mean age: 35 years) but not in elderly population (age range: 55–72 years) . The possible reason might be that the estrogen, which suppressed the progression of arteriosclerosis, decreased in postmenopausal women. Thus, gender difference in CIMT was weakened in elderly population as observed by Sinning et al. However, our subjects were patients with diabetics, which is an important and independent risk factor of CVD. Hayashi et al reported gender difference in CVD risk factors , which may cause gender difference in CIMT. Moreover, men are more susceptible to CVD risk factor than women [28–30]. Therefore, gender difference in CIMT was significant in our study due to diabetic status.
Another main finding of our study was that CIMT progression was faster in men than women, which was in keeping with other studies [24, 31]. Stensland-Bugge et al reported that the average progression per year of CIMT was greater in men than in women (0.010 mm versus 0.009 mm, P < 0.01) . In the present study, these value were 0.030 mm for men and 0.022 mm for women (P < 0.01). The progression of CIMT in our study was higher than those reported from healthy population (0.007 mm/year in Germen, 0.008 mm/year in Japanese) [32, 33] and similar to those reported from subjects with impaired glucose tolerance  and T2DM . In the current study, after adjustment for other covariables, age was an independent risk factors of CIMT progression only in men. This might be the reason that men had higher CIMT than women and this gender difference was more significant in patients with old age and more significant after a 4-year follow-up.
The present study must be interpreted within the context of its limitations. First, we did not find gender difference in the incidence of cardiovascular diseases or microvascular diseases after a 4-year follow-up, although men had higher CIMT than women at baseline. This might be due to the small sample size and the relatively short follow-up period. Second, we did not categorize anti-diabetic treatment, which might have effect on the results.