Adiposity in relation to age at menarche and other reproductive factors among 300 000 Chinese women: findings from China Kadoorie Biobank study

Abstract

Background: Adiposity is increasing rapidly in China but little is known about the relevance to it of women's reproductive factors, which differ inter-generationally and from that in the West. We assess associations of adiposity with life-course reproductive factors in Chinese women.

Methods: In 2004-08, the nationwide China Kadoorie Biobank recruited 303 000 women aged 30-79 (mean 50) years from 10 diverse regions. Multivariable linear regression was used to examine associations of reproductive factors (e.g. age at menarche/first birth/menopause, parity, breastfeeding and reproductive years) with measures of general [e.g. body mass index (BMI)] and central [e.g. waist circumference (WC)] adiposity in adulthood.

Results: Overall, the mean BMI was 23.7 (standard deviation 3.3) kg/m 2 , mean age at menarche was 15 (2) years and nearly all had given birth (99%) and breastfed children (98%). Adiposity was associated inversely with age at menarche and at first birth, with 0.19 and 0.05 kg/m 2 lower BMI and 0.38 and 0.12 cm lower WC per 1-year delay respectively ( P < 0.001). Among 128 259 post-menopausal women, adiposity was associated positively with age at menopause and reproductive years, with 0.05 and 0.07 kg/m 2 higher BMI and 0.12 and 0.17 cm higher WC per 1-year increase, respectively ( P < 0.001). The proportion with overweight/obesity had similar associations with these reproductive factors. Adiposity had a non-linear positive association with parity, but no association with breastfeeding duration.

Conclusion: Among Chinese women, earlier age at menarche and at first birth, later age at menopause and longer reproductive years were independently associated with increased adiposity late in life.

Keywords: Chinese; adiposity; cross-sectional studies; reproductive factors; women.

Figure 1.

Body mass index (BMI) and waist circumference (WC) vs age at menarche among all women, age at menopause and total reproductive years among post-menopausal women only. The means of each anthropometric measure was adjusted for age, region, education, household income, smoking, alcohol and physical activity. Analyses of age at menopause and reproductive years were only conducted among post-menopausal women, with additional adjustment for other reproductive factors. Closed squares represent the means of anthropometric measures with area inversely proportional to the variance of the mean and the vertical lines represent the corresponding 95% confidence intervals.

Figure 2.

Body mass index (BMI) and waist circumference (WC) vs number of live births in women and number of children fathered in men. The means of each anthropometric measure was adjusted for age, region, education, household income, smoking, alcohol and physical activity. Closed squares and solid lines represent the means of anthropometric measures for women whereas open squares and dash lines represent the means for men. Other conventions as in Figure 1.

Figure 3.

Body mass index (BMI) and waist circumference (WC) vs age at first birth and breastfeeding duration per child among parous women only. Conventions as in Figure 1 and the analyses were further adjusted for age at menarche and parity.

Figure 4.

Change in BMI associated with 1-year increase of (a) age at menarche among all women and (b) age at first birth among parous women only in certain population subgroups. The analysis was adjusted for age, area and other lifestyle factors (where appropriate). Each closed square represents a change in BMI per year increasing. The dotted vertical line indicates the overall change in BMI; the open diamond indicates it and its 95% confidence interval.