Body mass index and age at natural menopause: a meta-analysis

There is no universal consensus on the relationship between body mass index (BMI) and age at natural menopause (ANM). The primary bias was confounding by cigarette smoking because smoking was a strong confounding factor related to lower BMI and earlier menopause. This meta-analysis was conducted to estimate the effect of BMI on ANM.

Medline and EMBASE databases were searched for relevant studies up to December 2013. Studies were selected for analysis based on certain inclusion and exclusion criteria. Hazard ratios (HRs) with 95% CI were extracted to assess the association between BMI and early ANM.

Nine studies were selected for this meta-analysis. The HR of early ANM was 1.08 (95% CI, 1.03-1.14; P < 0.01) in underweight women compared with women of normal BMI. Compared with women of normal BMI, overweight women (HR, 0.93; 95% CI, 0.91-0.96; P < 0.001) and obese women (HR, 0.95; 95% CI, 0.79-1.15; P = 0.59) were associated with late ANM. In addition, the HRs of early ANM in overweight and obese women were 0.92 (95% CI, 0.90-0.94; P < 0.001) and 0.88 (95% CI, 0.82-0.95; P < 0.001), respectively, compared with underweight women. A separate meta-analysis indicated that the results (HR, 0.85; 95% CI, 0.81-0.90; P < 0.001) changed markedly in the comparison of obese versus normal-weight women in studies that controlled for smoking.

The results of our study indicate that increased BMI modestly associates with later ANM. The relationship between BMI and ANM needs further clarification in well-designed studies, especially studies well-controlled for smoking status.