Parity associated with telomere length among US reproductive age women

STUDY QUESTION: Is telomere length related to parity among a nationally representative sample of US reproductive age women? SUMMARY ANSWER: History of live birth was associated with shorter telomere length. WHAT IS KNOWN ALREADY: Shorter telomeres have been linked with a range of chronic health conditions and mortality and parity has been associated with health indicators. However, there is a lack of research on how parity relates to telomere length. STUDY DESIGN, SIZE, DURATION: This nationally representative, cross-sectional study included 1954 women from the National Health and Nutrition Examination Survey, 1999-2002, the only survey period which includes measurement of telomere length. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women aged 20-44 were included. Parity, defined as number of previous live births, was ascertained by questionnaire. Leukocyte telomere length was measured by polymerase chain reaction and reported as a ratio in relation to standard reference DNA (T/S ratio). The relationship between leukocyte T/S ratio and parity was examined using survey weighted linear regression. Models were adjusted for race/ethnicity, age, BMI, income-to-poverty ratio, education, early age at menarche and smoking status. MAIN RESULTS AND THE ROLE OF CHANCE: Among reproductive age women in the US, the adjusted mean leukocyte T/S ratio was 4.2% (95% CI: 0.9, 7.3) shorter in parous compared with nulliparous women. Parity was associated with 116 fewer base pairs (95% CI: 26, 204) on average, using estimated coefficients from the adjusted linear regression models and mean covariate values. LIMITATIONS REASONS FOR CAUTION: This study was cross-sectional and therefore was unable to establish temporality. The dataset lacked information on social factors, stress and fertility status, which may help explain these findings. Only two previous studies have examined this question and our findings should be interpreted with caution. WIDER IMPLICATIONS OF THE FINDINGS: These findings in a nationally representative sample of US reproductive age women suggest that history of live birth may be associated with accelerated cellular aging. The magnitude of the observed association was greater than that of the impact of smoking or obesity on telomere length, suggesting that parity may have an independent influence on cellular aging and warrant further study. STUDY FUNDING/COMPETING INTEREST(S): The study was funded in part by the Undergraduate Research Scholars Program at George Mason University. The authors have no conflicts of interest.