By: Dylan Gallegos
Editor’s Note: Former FACTS elective student and medical resident, Dylan Gallegos, summarized a study exploring the potential connection between caffeine intake and reproductive-aged women’s hormone levels and ovulatory function, with a focus on race-based differences. The research article, “Caffeinated beverage intake and reproductive hormones among premenopausal women in the BioCycle Study,” [1] was published in the American Journal of Clinical Nutrition in 2012.
Introduction
Studies have shown that approximately 89% of reproductive-aged women consume about 166 mg of caffeine per day (about 1.5 to 2 cups of coffee). Although caffeinated beverages are consumed at high rates, there is inconclusive and limited data on the consumption of caffeine and its effects on reproductive hormones. The primary objective of this study was to assess the relationship between caffeine intake and reproductive hormones in healthy premenopausal women and evaluate differences between races, if any. Secondly, researchers sought to determine whether or not caffeine is associated with incidental anovulation. Development and assessment of these associations is critical to craft guidelines regarding caffeine consumption levels for women in their reproductive years.
Methodology
The BioCycle study by Shliep et al. was conducted between 2005 and 2007 in western New York. The study followed premenopausal women, ages 18 to 44 years old, who were menstruating regularly, with a self-reported cycle length between 21 and 35 days for each menstrual cycle in the past 6 months. Additionally, participants were not on any form of hormonal contraception at the time of the study or the three months prior. Participants provided fasting blood samples eight times per cycle. Fertility monitors were used to assess menstrual cycle timing to determine when to draw samples. Estradiol, progesterone, luteinizing hormone (LH), follicle stimulating hormone (FSH), sex hormone binding globulin (SHBG), and insulin were all measured. Participants also completed 24-hour dietary recall (HDR) during check-ups to assess food and beverage intake.
Results
Primary study findings revealed that white women who consumed more than 200 mg of caffeine per day exhibited a decreased amount of free serum estradiol. Conversely, Asian women exhibited an increase in free estradiol levels and LH. Black women experienced both increased estradiol and decreased FSH levels. Both soda and green tea intake were associated with increased estradiol levels across all races. The only beverage associated with anovulation was green tea; however, the sample size for women who reported drinking green tea was small.
“Both soda and green tea intake were associated with increased estradiol levels across all races.”
Discussion
The American College of Obstetricians and Gynecologists (ACOG) recommends moderate caffeine consumption, defined as less than 200 mg caffeine daily, or two small cups of coffee a day. It is unclear whether caffeine intake at the recommended amount is more likely to be beneficial or harmful in reproductive-aged women who are not pregnant. The study results suggest caffeine consumption at the recommended levels is associated with slightly lower estrogen levels among white women, but has no effect on ovulatory function. While estrogen is a critical hormone for a woman’s healthy menstrual cycle function, high estrogen levels in some women may increase risk of breast and ovarian cancer. In a follow-up study among the same BioCycle participants, Schliep et al. found serum caffeine to be associated with reduced testosterone levels and a lower risk of sporadic anovulation. [2]
“The study results suggest caffeine consumption at the recommended levels is associated with slightly lower estrogen levels among white women, but has no effect on ovulatory function.”
In addition to varying effects on hormones observed across races, caffeine has also been observed in animal models to impact aromatase, inhibiting this key enzyme responsible for converting androgens to estrogen. Interestingly, the effect of caffeine as an aromatase inhibitor may benefit the population of women diagnosed with polycystic ovary syndrome (PCOS) as these patients may have elevated endogenous estrogen levels. Thus, caffeine may counter the estrogen dominance observed in PCOS. Presently, letrozole (an aromatase-inhibiting drug) is utilized in PCOS patients to induce ovulation and decrease serum estrogen. Future research might consider monitoring changes in reproductive hormone levels, symptoms, and fecundity in PCOS patients with varied caffeine intake.
In addition to the short-term effects of caffeine, there is also a need for long-term research observing the effects of caffeine intake on bone mineral density between healthy post-menopausal women and women with a history of PCOS. Such a study could more accurately assess the benefits of caffeine consumption for women diagnosed with this metabolic syndrome. Anovulation and infertility present real obstacles for women with PCOS, and combining information about lifestyle factors, such as caffeine consumption, with the information gleaned from charting a woman’s natural signs of fertility allows a woman and her clinicians to better monitor her health.
References
[1] Schliep KC, Schisterman EF, Mumford SL, et al. Caffeinated beverage intake and reproductive hormones among premenopausal women in the BioCycle Study. Am J Clin Nutr. 2012;95(2):488-497. doi:10.3945/ajcn.111.021287
[2] Schliep KC, Schisterman EF, Wactawski-Wende J, et al. Serum caffeine and paraxanthine concentrations and menstrual cycle function: correlations with beverage intakes and associations with race, reproductive hormones, and anovulation in the BioCycle Study. Am J Clin Nutr. 2016;104(1):155-163. doi:10.3945/ajcn.115.118430
ABOUT THE AUTHOR
Dylan Gallegos
Dylan completed medical school at the Burrell College of Osteopathic Medicine at New Mexico State University. He is currently doing his obstetrics and gynecology residency at Las Palmas Del Sol Healthcare in El Paso, TX. Dylan participated in both Parts A and B of the FABM elective and hopes to utilize the fertility awareness-based methods he learned during the elective with his future patients.
Inspired by what you read?
You can support the ongoing work of FACTS here. To connect with a member of our team, please email development@FACTSaboutFertility.org. Interested in becoming an individual or organizational member? You can learn more and register here. To discuss with a member of our team, please email membership@FACTSaboutFertility.org.
