Do physical activity, sitting time and body mass index affect fertility over a 15-year period in women? Data from a large population-based cohort study

Abstract

STUDY QUESTION Do physical activity (PA), sitting time (ST) and body mass index (BMI) affect fertility over a 15-year period in Australian women? SUMMARY ANSWER Moderate and high levels of PA confer advantages for fertility in women with normal BMI, but increased risk of infertility was observed in obese women. WHAT IS KNOWN ALREADY Higher BMI is positively associated with higher rates of problems with fertility, but the effects of physical activity and sitting time on fertility are less well understood. STUDY DESIGN, SIZE, DURATION Participants in The Australian Longitudinal Study of Women’s Health (ALSWH) completed mailed surveys in 2000, with follow-ups in 2003, 2006, 2009, 2012 and 2015 (N = 6130). PARTICIPANTS/MATERIALS, SETTING, METHODS Participants were aged 22 to 27 in 2000. They were asked to report their physical activity levels, sitting time and fertility problems in each survey from 2000 to 2015. BMI was calculated from self-reported weight and height. Cumulative incidence of fertility problems was calculated from 2000 to 2015 and hazard ratios (HR) and 95% CIs were calculated using survival analysis. MAIN RESULTS AND THE ROLE OF CHANCE From 2000 to 2015, the cumulative incidence of fertility problems was 15.4% (95% CI: 14.5–16.4). High levels of PA were associated with reduced risk of problems with fertility [HR 0.82 (95% CI: 0.69–0.98)], and higher BMI was positively associated with fertility problems [overweight: HR 1.18, (95% CI 0.99–1.39); obese: HR 1.36, (95% CI 1.14–1.63)]. In survival analyses, incidence rates were highest in every survey interval in women who reported low PA levels and in women who were obese. Overall, ST was not associated with fertility problems. In stratified models, high levels of PA attenuated the risk of problems with fertility in women who were in the normal BMI category [HR 0.64, (95% CI 0.49–0.82)]. LIMITATIONS, REASONS FOR CAUTION The ALSWH relies on self-reported data, which may be subject to recall bias. WIDER IMPLICATIONS OF THE FINDINGS The study provides estimates of problems with fertility in a cohort of young adult Australian women, and the results indicate that these are inversely associated with physical activity levels and positively associated with BMI. However, the high infertility risk in obese women was not attenuated by high levels of PA. The protective effects of PA were only observed in women with normal BMI. As rates of developing problems with fertility were highest in every survey interval among women who reported low levels of physical activity and in women who were obese, these findings suggest that improving physical activity levels could be an affordable strategy to reduce problems with fertility in women who are trying to conceive. These findings should be considered by clinical and public health practitioners. STUDY FUNDING/COMPETING INTEREST(S) The ALSWH is funded by the Australian Government. Funding for these analyses was provided by a University of Queensland (UQ) International Postgraduate Research Scholarship and a UQ International Development Fellowship. The authors declare no conflicts of interest.

Trajectories and determinants of weight gain in two cohorts of young adult women born 16 years apart

“…If our projections are ratified, the health effects for our millennial cohort will be profound. With average BMI in the obese category, there will be increases in 'mainstream' NCDs such as CVD, diabetes, cancers, osteo-arthritis and mental health problems, and in numerous less frequently cited consequences of obesity such as incontinence, cataracts, and reproductive health problems [15,[29][30][31][32]. This will mean increased health care costs, as previous analyses of ALSWH data have already shown that health care costs are significantly higher for women in the obese BMI category until at least 78 years of age, and that Australian women with obesity have almost twice the number of prescriptions and higher pharmaceutical costs across the lifespan than women with healthy weight [33].…”

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“…In addition, many women trying to conceive lead unhealthy lifestyles that affect their chances of becoming pregnant ( 7 , 8 ). Risk factors include poor diet ( 9 , 10 ), being overweight or obese, a sedentary lifestyle ( 11 ), tobacco use, and high levels of anxiety or depression ( 12 ), among others ( 13 ). Moreover, women's pre-conception lifestyle can not only decrease natural fertility, but also affect the results of fertility treatments.…”

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“…Among overweight/obese women (BMI ≥25 kg/m 2 ), fecundability was 27% higher for vigorous PA of ≥5 versus <1 h/week (Figure 3) [151]. In another cohort study, analyzing Australian women over a 15-years period, a lower risk of fertility issues was observed in the highly active and normal weight women, while a higher risk was observed in the obese women [152].…”