Adiposity and insulin resistance as mediators between age at menarche and type 2 diabetes mellitus

Genetic prediction of age at menarche, age at natural menopause and type 2 diabetes: A Mendelian randomization study

BACKGROUND AND AIMS

The relationship between reproductive factors and type 2 diabetes (T2D) is controversial; therefore, we explored the causal relationship of age at menarche (AAM), age at natural menopause (ANM), with the risk of T2D and glycemic traits using two-sample Mendelian randomization.

METHODS AND RESULTS

We used publicly available data at the summary level of genome-wide association studies, where AAM (N = 329,345), ANM (N = 69,360), T2D (N = 464,389). The inverse variance weighting (IVW) method was employed as the primary method. To demonstrate the robustness of the results, we also conducted various sensitivity analysis methods including the MR-Egger regression, the weighted median (WM) and the MR Pleiotropy RESidual Sum and Outlier (MR-PRESSO) test. After excluding IVs associated with confounders, we found a causal association between later AAM and reduced risk of T2D (OR 0.81 [95% CI 0.75, 0.87]; P = 2.20 × 10^-8), lower levels of FI (β -0.04 [95% CI -0.06, -0.01]; P = 2.19 × 10^-3), FPG (β -0.03 [95% CI -0.05, -0.007]; P = 9.67 × 10^-5) and HOMA-IR (β -0.04 [95% CI -0.06, -0.01]; P = 4,95 × 10^-3). As for ANM, we only found a causal effect with HOMA-IR (β -0.01 [95% CI -0.02, -0.005]; P = 1.77 × 10^-3), but not with T2D.

CONCLUSIONS

Our MR study showed a causal relationship between later AAM and lower risk of developing T2D, lower FI, FPG and HOMA-IR levels. This may provide new insights into the prevention of T2D in women.

Mediation Effect of Obesity on the Association of Age at Menarche With Blood Pressure Among Women in Southwest China

Background Previous studies have been inconsistent about the association between age at menarche and high blood pressure. Little is known about such association across a wide range of menarcheal ages in less developed ethnic minority regions in China. We aimed to explore the association between age at menarche and high blood pressure (BP; ≥140/90 mm Hg) and to examine the mediating effect of obesity and the moderating effect of menopausal status on this association. Methods and Results A total of 45 868 women from the baseline data of the CMEC (China Multi-Ethnic Cohort) were included in this study. Binary logistic regression was used to analyze the relationship between age at menarche and high BP, and the mediation model was used to evaluate the mediating effects of body mass index and waist circumference on the association of age at menarche with high BP. The mean age at enrollment and age at menarche of participants in our study were 49.3 (SD=10.7) and 14.7 (SD=2.1) years, respectively. Late menarche was associated with a lower risk of high BP (odds ratio, 0.831 [95% CI, 0.728-0.950]). The risk of high BP decreased by 3.1% with each year's delay in the onset of menarche (P for trend <0.001). Body mass index and waist circumference could partially mediate the association of age at menarche and high BP with the indirect effect of body mass index (odds ratio, 0.998 [95% CI, 0.997-0.998]) and waist circumference (odds ratio, 0.999 [95% CI, 0.998-0.999]). In addition, the mediation effects were modified by the status of menopause. Conclusions Women with late menarche have a lower risk of high BP, and obesity could be one of the important mediators. Obesity prevention is an efficient strategy to reduce the association between age at menarche and high BP, especially in premenopausal women.

Mendelian randomization identifies age at menarche as an independent causal effect factor for gestational diabetes mellitus

AIMS

The relationship between age at menarche (AAM) and gestational diabetes mellitus (GDM) risk is still inconclusive. This Mendelian randomization (MR) analysis was used to assess systematically the causal relationship between AAM and GDM risk in human beings.

MATERIALS AND METHODS

Single-nucleotide polymorphisms associated with AAM, oestradiol levels, sex hormone-binding globulin (SHBG) levels and bioavailable testosterone (BioT) levels were screened via the genome-wide association study enrolling individuals of European descent. Summary-level data for GDM (123 579 individuals) were extracted from the UK Biobank. An inverse-variance-weighted method was used for the primary MR analysis. Sensitivity analyses were examined via MR-Egger regression, heterogeneity tests, pleiotropy tests and leave-one-out tests. The directionality that exposure causes the outcome was verified using the MR-Steiger test.

RESULTS

Genetically predicted early AAM was found to have a causal positive association with a higher risk of GDM (odds ratio = 0.798, 95% confidence interval = 0.649-0.980, p = .031). In the multivariable MR analysis adjusted for oestradiol, SHBG and BioT levels, the causal association between AAM and GDM risk remained (odds ratio = 0.651, 95% confidence interval = 0.481-0.881, p = .006). A 1-SD increase in SHBG or BioT levels was significantly associated with a 41.4% decrease or 20.8% increase in the overall GDM risk (p = 3.71E-05 and .040), respectively. However, after controlling for AAM, oestradiol levels and BioT levels by multivariable MR analysis, there was no direct causal effect of SHBG levels on GDM risk (p = .084). Similarly, after adjusting for AAM, oestradiol levels and SHBG levels by multivariable MR analysis, there was no direct causal effect of BioT levels on the risk of GDM (p = .533). In addition, no direct causal association was identified between oestradiol levels and GDM risk in univariable MR analysis or multivariable MR analysis.

CONCLUSION

Genetic variants predisposing individuals to early AAM were independently associated with higher GDM risk. Further research is required to understand the mechanisms underlying this putative causative association. In addition, AAM may be helpful in clinical practice to identify women at risk for GDM; pregnant women who are young for menarche may need to take precautions before GDM develops.

Systolic blood pressure as the mediator of the effect of early menarche on the risk of coronary artery disease: A Mendelian randomization study

Background

Menarche timing may not be directly associated with the risk of coronary artery disease (CAD). Therefore, we investigated the roles of metabolic factors in explaining the effect of age at menarche on CAD risk.

Methods

We identified women with age at menarche and CAD by using three analytical methods: Mendelian randomization (MR), logistic regression analysis, and Cox proportional hazard regression. The first two analyses were performed in the Taiwan Biobank (N = 71,923) study, and the last analysis was performed in the Chin-Shan Community Cardiovascular Cohort study (N = 1,598). We further investigated the role of metabolic factors in mediating the effect of age at menarche on CAD risk by using three complementary methods with mediation analyses.

Results

One standard deviation of earlier age at menarche was associated with a 2% higher CAD risk [odds ratio = 1.02, 95% confidence interval (CI) = 1.001-1.03] in the MR analysis, an 11% higher risk (odds ratio = 1.11, 95% CI = 1.02-1.21) in the logistic regression analysis, and a 57% higher risk (hazard ratio = 1.57, 95% CI = 1.12-2.19) in the Cox proportional hazard regression. All the analyses consistently supported the role of systolic blood pressure in mediating this effect. The MR results indicated that 29% (95% CI = 26%-32%) of the effect of genetically predicted earlier age at menarche on CAD risk was mediated by genetically predicted systolic blood pressure.

Conclusion

The results obtained using different analytical methods suggest that interventions aimed at lowering systolic blood pressure can reduce the cases of CAD attributable to earlier age at menarche.