Aaron K. Styer MD, associate director of the Basic Science Research Program for the Reproductive Endocrinology & Infertility Fellowship at Mass General
"Will my daily caffeine intake reduce my fertility?" This is perhaps one of the more commonly asked questions by women trying to conceive.
The most studied lifestyle habits, smoking and alcohol, have garnered much attention over the past decade, as possible common causes of reduced fertility. Because of its prevalence in the Western diet, caffeine has also been studied extensively by many investigators as a potential harmful factor in connection with fertility. Caffeine is knowingly and unknowingly consumed daily by women worldwide and is present in a variety of dietary sources such as soft drinks, tea, coffee, chocolate, and several over the counter medications.
Despite an extensive list of publications investigating the effect of dietary caffeine on fertility, there have been conflicting reports. Some have demonstrated an association of caffeine with infertility, while others have not shown any obvious adverse effects on a couple’s ability to conceive. Interestingly, there have even been small scale studies which demonstrate improved fertility with certain caffeinated beverages.
Much publicity has recently been generated by an article released earlier this year entitled "Inhibitory effect of caffeine on pacemaker activity in the oviduct is mediated by cAMP-regulated conductances". This study published in the British Journal of Pharmacology by investigators from the University of Nevada School of Medicine, highlights a potential role of caffeine in reducing fertility and delaying conception by slowing the transport of the egg through the fallopian tube.
In this study, the authors utilized mice to assess the effects of caffeine on smooth muscle contraction in the fallopian tubes of these animals. Muscle activity in this model is thought to facilitate transport of the mouse egg through the oviduct (fallopian tube) prior to fertilization by sperm and subsequent conception. Based upon their findings, they report that increasing caffeine concentrations progressively reduced the muscle activity vital to egg transport in the oviduct. The authors concluded that these results could imply that excessive caffeine consumption may result in impaired transport of the egg and reduced conception rates in humans.
Although the findings of this publication are intriguing, and this group should be commended for investigating the effects of caffeine in a female reproductive system model, it would be premature to confidently assume that the findings and conclusions of this study can be applied to human infertility. Since this study was performed in mice and the caffeine treatments were mainly performed in an in vitro system (outside of the body), it would not be prudent to make any conclusions regarding caffeine use and human fertility based upon these results.
Because the majority of previous studies analyzing the association between caffeine and fertility are retrospective and employed many different study designs, there are inherent biases and study flaws which may contribute to a lack of consensus of results. Although researchers have proposed that caffeine may negatively affect a woman’s ability to ovulate (release an egg), and reduce fertility rates, there has not been any study to clearly demonstrate this.
Early studies in the late 1980’s concluded that caffeine intake greater than 250 mg per day (approximately 11 oz of brewed coffee) were associated with decreased fertility. Unfortunately, these studies were also retrospective, only small numbers of patients were studied, and they contained biases and confounders which did not account for factors, other than caffeine, which may have caused infertility.
One notable study by investigators at the Harvard School of Public Health prospectively followed greater than 18,000 married women enrolled in the Nurses’ Health Study for 8 years, as they attempted to conceive (Chavarro JE et al. Epidemiology 2009; 20(3): 374-381). This well designed and appropriately powered study did not find that caffeine intake impaired ovulation to the point of decreasing fertility. Unlike most studies, this was a comprehensive prospective analysis, and examined a very large number of patients over an appropriate period of time.
Our professional and personal lives are filled with stressors, and many of us indulge in a daily ritual of caffeinated beverages or snacks to navigate routines. When faced with the anxieties of trying to conceive, and the prospect of infertility, many "comfort items", which happen to be caffeinated, may be difficult to completely eliminate. Despite a large number of available studies, we are still faced with a sizeable collection of inconsistent data and some uncertainties. Questions which beckon answering include:
1. Does caffeine intake have a consistently negative effect on a woman’s ability to conceive?
2. If caffeine does have a negative impact on conception rates, is there a specific amount of daily caffeine consumption which poses an increased risk of infertility?
Although we are reassured that there is no consistent evidence supporting a negative effect of routine dietary caffeine on woman’s fertility, there is also a lack of evidence to exclude caffeine as a contributing factor to infertility. Most frustrating to patients and practitioners is the fact that there is no uniform counseling or evidence based guidelines available. We are all hopeful that future studies will allows us to answer the above questions more definitively. Until then, we can rely on expert opinion which suggests that moderate caffeine consumption (e.g. 1-2 cups of coffee per day or its equivalent) before or during pregnancy has no apparent negative effects on fertility or pregnancy outcomes (Practice Committee of the American Society for Reproductive Medicine, Fertil Steril 90 (suppl3) 2008; S1-S6.).
For now, it seems that mild to moderate daily caffeine intake does not affect fertility. As with anything in life…everything in moderation…including caffeine.
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