The Mediating Role of Body Mass Index in the Association Between Age at First Childbirth and Lung Function Among Chinese Postmenopausal Women

Abstract

Objective

Little is known about the effect of age at first childbirth on lung function. We aimed to investigate the association between age at first childbirth and lung function in Chinese women and further test whether this association is mediated by body mass index (BMI).

Methods

This cross-sectional study is a partial survey of the China Kadoorie Biobank (CKB) which was conducted in Xinxiang City, Henan Province between 2004 and 2008. A total of 16,584 postmenopausal women aged 30–79 years were enrolled. Multiple linear and logistic regression were used to investigate the association between age at first childbirth and lung function and overweight/obesity. The mediation analysis was performed using the PROCESS procedure for SPSS.

Results

The mean (SD) age at first childbirth was 23.1 (2.7) years. Women with first childbirth aged ≤19 years and 20–22 years had lower lung function than women who gave first childbirth aged 23–25 years. Per 1-year increase in the age at first childbirth was associated with a 3.31 mL increase in FEV1 (95% CI = 1.27–5.35), 3.91 mL increase in FVC (95% CI = 1.63–6.18), 0.15% increase in FEV1, % predicted (95% CI = 0.05–0.24) and 0.14% increase in FVC, % predicted (95% CI = 0.05–0.22). There was no clear association between age at first childbirth and FEV1/FVC ratio. BMI played a contribution to the association between age at first childbirth and FEV1 and the proportion was 16.4% (indirect effect: β = 0.65, 95% CI = 0.46–0.89; total effect: β = 3.96, 95% CI = 1.92–5.99). Similarly, the proportion to FVC, FEV1, % predicted, and FVC, % predicted was 25.0%, 16.6%, and 25.0%, respectively.

Conclusion

Early age at first childbirth was associated with lower lung function and BMI mediated the association. It is important to test lung function and popularize the knowledge of weight control in women who gave first childbirth at an early age.

Keywords:

• first childbirth
• lung function
• body mass index
• mediation
• postmenopausal women

Data Sharing Statement

Huizi Tian, Kai Kang, and Shixian Feng had full access to all of the data in the study and take responsibility for the integrity of the data.

Ethics Approval and Consent to Participate

All procedures in our study were in line with the Declaration of Helsinki. The study was approved by the ethics committees of the University of Oxford and the Chinese Center for Disease Control and Prevention (CDC). In addition, ethics approval was also obtained from the institutional research board at the Henan Provincial CDC and Huixian CDC. All participants provided written informed consent.

Acknowledgments

We thank the Chinese Center for Disease Control and Prevention, the Chinese Ministry of Health, the National Health and Family Planning Commission of China, and provincial/regional Health Administrative Departments. The most important acknowledgment is to the participants in the study and the members of the survey teams in Xinxiang City, Henan Province, as well as to the project development and management teams based in Beijing, Oxford.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis, and interpretation, or in all these areas; took part in drafting, revising, or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare no conflicts of interest in this work.

Additional information

Funding

This work was supported by grants (2016YFC0900500, 2016YFC0900501) from the National Key Research and Development Program of China, grants from the Kadoorie Charitable Foundation in Hong Kong, and grants (202922/Z/16/Z, 088158/Z/09/Z, 104085/Z/14/Z) from Wellcome Trust in the UK.