Background: Many epidemiologic studies have evaluated the association between caffeine and fertility, with inconsistent results. Some studies suggest that various caffeine-containing beverages may affect fertility differently.
Methods: We evaluated the relation of caffeine, coffee, tea, and sodas with time to pregnancy in a prospective cohort study of 3628 women planning a pregnancy, in Denmark (2007–2010). Women reported beverage intake at baseline and every 8 weeks during follow-up until they became pregnant or for up to 12 cycles. We used discrete-time Cox proportional hazards regression to estimate fecundability ratios (FRs) and 95% confidence intervals (CIs), controlling for potential confounders.
Results: There was little relation between fecundability and caffeine intake of 300+ mg/day compared with <100 mg/day (FR = 1.04 [95% CI = 0.90–1.21]) or coffee intake of 3+ servings/day compared with none (1.05 [0.85–1.33]). Soda consumption was associated with reduced fecundability: for all types of sodas combined, the adjusted FRs were 0.89 (0.80–0.98), 0.85 (0.71–1.02), 0.84 (0.57–1.25), and 0.48 (0.21–1.13) for <1, 1, 2, and 3+ servings per day, respectively, compared with none. Tea drinking was associated with a slight increase in fecundability, with FR = 1.27 (0.98–1.64) for 2+ servings/day versus none.
Conclusion: In this prospective study of time to pregnancy, the association between caffeine intake and fertility differed by beverage type. Although we controlled for many confounders, our findings of reduced fecundability among soda drinkers and increased fecundability among tea drinkers could have resulted from confounding by unmeasured lifestyle characteristics.
From the aDepartment of Epidemiology, Boston University School of Public Health, Boston, MA; bSlone Epidemiology Center, Boston University, Boston, MA; cDepartment of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; and dRTI Health Solutions, Research Triangle Park, NC.
Submitted 30 June 2011; accepted 14 November 2011; posted online 8 March 2012.
This study was supported by the National Institute for Child Health and Development (R21-050264 and R01-060680) and the Danish Medical Research Council (271-07-0338). The authors reported no other financial interests related to this research.
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Correspondence: Elizabeth E. Hatch, Boston University School of Public Health, Department of Epidemiology, 715 Albany St., Boston, MA. E-mail: firstname.lastname@example.org.