4.2 | Results in the context of what is known
To our knowledge, there is no large-scale, population-based, longitudinal study evaluating the association between presence of UL and development of type 2 diabetes mellitus in young women. This study revealed that UL was associated with an elevated risk for type 2 diabetes mellitus and that myomectomy seemed to attenuate the risk for type 2 diabetes mellitus in young women with UL.
Several studies indicate an association between obesity and UL.2,12,13 Ciavattni et al. performed an observational case-control study including 71 women of childbearing age diagnosed with UL and 145 women as control group.12 Women with UL had higher BMI (P = 0.0034), preperitoneal fat thickness (P< 0.0001), and subcutaneous fat thickness (P = 0.0003); however, only preperitoneal fat thickness showed an independent significant association with the presence of UL in multivariate analysis (P < 0.0001). Another study, including 89 patients with UL and 81 healthy women without UL, showed that increased body fat (especially abdominal visceral fat) is associated with an increased risk of UL.13 Recently, a meta-analysis examining 24 studies found a positive association between obesity and the risk/prevalence of UL (odds ratio [OR] 1.19, 95% CI 1.09-1.29).2 Consistent with the result of previous studies, women with UL had a BMI higher than that of women without UL in our study, although both groups had relatively low BMI. However, in subgroup analysis stratified by BMI, women with BMI ≥25 kg/m2 revealed no significant difference in the incidence rate of type 2 diabetes mellitus between women with UL and without UL. This might be due to well-known close association between obesity and the development of type 2 diabetes mellitus. Relative high incidence rate of women with or without UL with BMI ≥25 kg/m2 compared to women with BMI less than 25 kg/m2 support this hypothesis (Table 3). Similarly, there was no difference in the incidence rate of type 2 diabetes mellitus between women with UL and without UL in whom with CKD history. These findings also might be due to the inseparable association between CKD and development of type 2 diabetes mellitus.14
Beyond obesity, several studies reported that various metabolic components were associated with UL.10,15 Takeda et al investigated whether UL is associated with any specific criteria of metabolic syndrome.15 In their case-control study, BMI, blood pressure, TG, and FPG were significantly higher in 213 women with UL compared to those in 159 women without UL. Moreover, the risk of UL was correlated with increased metabolic component levels; the OR of three metabolic components for UL was 3.64 (95%CI 2.28-5.82). Another study that enrolled 1,230 parous premenopausal women reported that women with UL had higher waist circumferences, body fat, blood pressure, and LDL cholesterol than women without UL.10 Increasing evidence suggests that UL seems to share pathogenic features with the development of metabolic syndrome. In our study, women with UL had poor metabolic profiles, such as higher blood pressure, FPG, total cholesterol, TG, LDL cholesterol, and lower HDL cholesterol, when compared with women without UL.
Although the two disease states are likely to be related, few studies have evaluated the association between UL and type 2 diabetes mellitus. A nested case-control study enrolling 3,789 participants reported a protective association between UL and type 2 diabetes with a relatively greater protective effect observed among European Americans than African Americans.16 However, this study was limited by design and population as it was a cross-sectional study that included relatively old women (mean age: 47 y in UL group; 44 y in control group). On the other hand, the previously mentioned study by Tak et al revealed that hyperglycemia is significantly associated with an increased risk of UL (OR: 1.45, 95%CI 1.10-1.89).10Furthermore, in a Taiwanese population-based cohort study, metformin use was associated with a lower risk of UL (HR: 0.467, 95%CI 0.387-0.564) in 21,996 women with new-onset type 2 diabetes mellitus.11 However, there was no longitudinal study to evaluate the risk for type 2 diabetes mellitus solely in connection with the presence of UL, especially in young women.