Socioeconomic position, lifestyle factors and age at natural menopause: a systematic review and meta-analyses of studies across six continents

Abstract

Background: Age at natural menopause (ANM) is considered a marker of biological ageing and is increasingly recognized as a sentinel for chronic disease risk in later life. Socioeconomic position (SEP) and lifestyle factors are thought to be associated with ANM.

Methods: We performed a systematic review and meta-analyses to determine the overall mean ANM, and the effect of SEP and lifestyle factors on ANM by calculating the weighted mean difference (WMD) and pooling adjusted hazard ratios. We explored heterogeneity using meta-regression and also included unpublished findings from the Australian Longitudinal Study on Women's Health.

Results: We identified 46 studies across 24 countries. Mean ANM was 48.8 years [95% confidence interval (CI): 48.3, 49.2], with between-study heterogeneity partly explained by geographical region. ANM was lowest among African, Latin American, Asian and Middle Eastern countries and highest in Europe and Australia, followed by the USA. Education was associated with later ANM (WMD middle vs low education 0.30, 95% CI: 0.10, 0.51; high vs low education 0.64, 95% CI 0.26, 1.02). A similar dose-response relationship was also observed for occupation. Smoking was associated with a 1-year reduction of ANM (WMD: -0.91, 95% CI: -1.34, -0.48). Being overweight and moderate/high physical activity were modestly associated with later ANM, but findings were less conclusive.

Conclusions: ANM varies across populations, partly due to differences across geographical regions. SEP and some lifestyle factors are associated with ANM, but further research is needed to examine the impact of the associations between risk factors and ANM on future health outcomes.

Keywords: Menopause; body mass index; meta-analysis; physical activity; smoking; socioeconomic factors; systematic review.

Figure 1.

Flow diagram of selection process and inclusion of studies for meta-analysis. ¹Studies by Dravta et al. (2009) and Ku et al. (2004) each included two study populations.

Figure 2.

Meta-analysis of mean age at natural menopause, stratified by geographical region (using random effects). CI, confidence interval. ^aChinese women in Taiwan; ^bsecond- or third-generation emigrants from Korea to China; ^cChinese Malay and Indian women in Singapore; ^dmean and standard error were calculated from the median and range using recommended formula; ^eStudy included centres from North, Central and South America (Argentina; Bolivia; Brazil; Chile; Colombia; Costa Rica; Cuba; Dominican Republic; Ecuador; Honduras; Mexico; Panama; Paraguay; Peru; Uruguay. Dotted line represents the overall summary mean age.

Figure 3.

Meta-analysis^a of the unadjusted effect of (a) middle education level, (b) high education level, (c) middle occupation level and (d) high occupation level on age of natural menopause. ^aRandom effects estimates. Third and fourth columns in the figures give the number of women classified as having a middle, high or low education level, and middle, high or low occupation level, as appropriate.

Figure 4.

Meta-analysis^a of the unadjusted effect of income on age of menopause. ^aRandom effects estimate.

Figure 5.

Meta-analysis^a of (a) the unadjusted effect of smoking on age of menopause and (b) the unadjusted effect of smoking on age of natural menopause, stratified by whether countries were ‘economically more developed regions’ or ‘other regions’.^b WMD, weighted mean difference; CI, confidence interval. ^aRandom effects estimates; ^bthe meta-analysis stratified by region excludes one outlying study (Cooper et al.), since the direction of the effect estimate for smoking was clearly contrary to all other studies, and the exclusion of which removed all heterogeneity among ‘economically more developed regions’. The third and fourth columns in each figure give the number of women who were classified as smokers and non-smokers in each study.

Figure 6.

Meta-analysis of the unadjusted effect of (a) overweight^a (b) obesity^b and (c) moderate/high physical activity^a on age of natural menopause. WMD, weighted mean difference; CI, confidence interval. ^aRandom effects estimate; ^bfixed effects estimate. Third and fourth columns in the figures give the number of women classified as being normal weight, overweight or obese, and moderately to highly physically active or physically inactive (low or no physical activity), as appropriate.