In the United States, 29 billion energy drinks and 146 billion cups of coffee are consumed yearly! Over 90% of adults report drinking coffee as one of the most commonly consumed beverages, second only to water. Among teens and young adults, energy drinks are the second most popular dietary supplement behind multivitamins(1). It’s not just the taste of these beverages that people enjoy; it's the health and performance benefits of caffeine!
Between reducing fatigue and increasing mental alertness, focus, and reaction time, caffeine's benefits are of interest to many people, especially athletes. There's long been concern regarding whether caffeine is safe for pregnant women. But with recent scrutiny to understand metabolic differences between the sexes, you may wonder how or if caffeine is helpful to women at all. Does caffeine help performance in female athletes the same as the research says it does for male athletes?
Let's first discuss how it works and where the research is to review whether caffeine is beneficial for female athletes.
Caffeine is an adenosine receptor antagonist that increases the release of stimulating neurotransmitters to increase arousal and reduce fatigue(2). In sports research, this has translated into more mental focus and attention and reduced time to exhaustion. Further benefits may include the promotion of fatty acid mobilization and shifting substrate utilization, which may be useful to some athletes(2). Despite the hundreds of dietary agents claiming to improve performance, the International Olympic Committee has narrowed down just four ingredients with good evidence to support ergogenic benefits for athletes – caffeine is one of them, along with creatine, buffering agents, and nitrates(3). Needless to say, athletes from endurance sports, like running and rowing, to power sports, like weight lifting or combat sports, and even to skill and focus sports, like darts and shooting, will likely benefit!
But do male and female athletes respond to caffeine the same? Is caffeine beneficial to female athletes?
Despite decades of research in caffeine, a 2022 review study discovered that from 2000-2021, only 15 studies on caffeine and performance enhancement have been conducted in a female-only population (4). Within those studies, only 7 controlled for the menstrual cycle or hormone status- but the methods of doing so were not uniform. Since hormones affect metabolism and caffeine clearance, and due to the wide range of hormones across a menstrual cycle, across a woman’s lifespan, and various uses of exogenous hormones and birth control methods, this is clearly a limiting factor in our understanding of how caffeine works in women and if caffeine is safe in women. Furthermore, out of these 15 studies reviewed in the article, all women were under age 40, with a mean age under 30, and training status widely varied from untrained to elite, highlighting even further research gaps.
So although we don’t know all the details as to whether caffeine is beneficial for female athletes especially women over 40, women in menopause, or women in varying stages of the menstrual cycle or with hormonal contraceptives- here is what we do know:
Without consideration of sex, the IOC Consensus Statement of Dietary Supplements and the High Performing Athlete concludes that optimal benefits of caffeine are observed in doses of 3-6mg/kg body weight. Adverse effects are observed at doses ≥9mg/kg, and in extremely high doses or in combination with other stimulants, caffeine may have fatal outcomes(3).
The International Society of Sports Nutrition's Position Stand on Caffeine and Exercise Performance offers strong support for the use of lower doses of caffeine (1–3 mg/kg of body mass) to activate the central nervous system, which can reduce pain and rate of perceived exertion, which may be helpful in endurance athletes (5).
One study by Astorino et al. (2012) supplemented female soccer payers with the energy drink Red Bull®, which contains only 1.3 mg/kg caffeine. There were no beneficial effects in the supplemented group on sprint time, rate of perceived exertion (RPE), or heart rate; however, the authors suggested that the 1.3 mg/ kg dose of caffeine was simply an insufficient amount (2).
Now in doses of 3-6mg/kg, specific to women, the results of caffeine's benefits to female athletes are certainly promising, though results are highly variable based on the type of performance being measured! Further, it's possible that men and women do metabolize caffeine differently- outlined in a few studies below. Last, variation in the CYP1A2 gene, which affects caffeine metabolism, may modify the ergogenic effects of caffeine, regardless of or independent of sex. The CYP1A2 gene was not necessarily investigated in the studies outlined below. So as always, further research is needed here. The bullet points below are direct quotes by Murphy et. al. in the 2022 review “Dietary Supplements for Athletic Performance in Women: Beta-Alanine, Caffeine, and Nitrate” to give insight to caffeine’s benefits for female athletes:
Norum et al. (2020) investigated the effects of acute supplementation of 4 mg/kg caffeine on strength and power in resistance-trained women and found significant improvements
Goldstein, Jacobs et al. (2010) found similar benefits to strength, but no notable improvements in endurance, with 6 mg/kg caffeine supplementation.
Using the same 6 mg/kg dosage, Ali et al. (2016) found that evening supplementation with caffeine in female teamsport athletes improved eccentric knee flexor performance both immediately after and the day after consumption. This study did not find a notable difference in strength, nor in peak power or concentric power.
Pérez-Lo´pez et al. (2015) found elite female volleyball players showed improvement for volleyball-specific performance measures, such as standing and jumping spike velocity, hand grip, jump height, and agility with 3 mg/kg caffeine ingested 60 min prior to exercise. Simulated game performance improved and the number of errors per game were reduced.
Krasňanová et al. (2014) found no notable improvement in floorball-specific shooting accuracy, standing long jump, or performance in the 6 × 9 m shuttle run in women supplemented with an average of 4.4 mg/kg caffeine (n = 14). There was a significant improvement in the average completion time of the longer, 6 × 40 m shuttle run (p < .01), which has been shown to reliably reflect power and anaerobic capacity
Stojanovi´c et al. (2019) investigated the effect of 3 mg/kg caffeine on the anaerobic performance of female professional basketball players (n = 10). Significant increases in 10 m (p = .05) and 20 m (p = .04) sprint times and a moderate decrease in RPE (p = .04) were reported in the supplemented group, along with nonstatistically significant improvements in squat jump (p = .08), agility (p = .12), and suicide run (p = .28) performance.
Del Coso et al. (2013) supplemented female “rugby sevens” players with 3 mg/kg caffeine in the form of a commercial energy drink. No effect of caffeine was seen on maximal running speed in sprint testing, but total leg muscle power in 15-s maximal jump testing and average running pace during simulated game play improved, showing some ergogenic benefits of the commercial drinks in this population of female rugby athletes.
Female soccer players who supplemented with 3 mg/kg caffeine from a commercial energy drink also saw improvements in mean jump height and peak power in a jump test, as well as an increased number and length of sprint bouts per game in simulated game play (Lara et al., 2014). Unlike the female rugby players, these supplemented female soccer players had increased average peak speed and maximal speed in a sprint test, though this did not translate to any significant difference in maximal speed (p = .25) during game play (n = 18).
Motl et al. (2006) found a significant reduction in midworkout pain perception (p = .001) in moderately trained college women given either 5 or 10 mg/kg caffeine before exercise (n = 11). Decreased perception of pain mid-workout could translate to longer or harder training sessions in women, leading to greater physiological adaptation to training.
Tinsley et al. (2017) compared the effects of both caffeinated and noncaffeinated commercial energy drinks on muscular force production in women and men (n = 21). The caffeinated energy drink contained 3.6 mg/kg caffeine, and the rest of the ingredients varied between the two drinks, save for a consistent 6 g citrulline malate in both beverages. The increases in strength seen in the results of a three rep max force production test in both men and women were statistically nonsignificant (p = .57). However, the differences between men and women in the improvements that did occur were much more pronounced in the noncaffeinated group (0%–1.5% increase for women, 9% for men) compared with the caffeinated group (5%–11% increase for women and men).
Skinner et al. (2019) examined the sex-based differences in 3 mg/kg caffeine supplementation on endurance cycling performance and found a significant increase in cycling time-trial (TT) performance with caffeine (p < .001), but no significant difference between sexes (p = .98) (n = 27). Notably, postexercise plasma concentrations of caffeine were significantly higher in women (p < .001) than in men, with only women experiencing significant pre- to postexercise increases in plasma caffeine concentration (p < .01).
While both studies by Tinsley et. al and Skinner et al. appear to demonstrate no difference in caffeine efficacy between sexes, the more pronounced increase in plasma caffeine concentration and greater benefit to strength performance compared with noncaffeinated energy drinks may support the idea of different metabolic responses to caffeine in women compared with men.
Potgieter et al. (2018) found a greater magnitude of response to 6 mg/kg caffeine in triathlon performance in men compared with women.
Chen et al. (2019) studied caffeine’s impact on delayed-onset muscle soreness and exercise-induced muscle damage in both male and female college athletes (n = 20). One hour after ingestion of 6 mg/kg caffeine, men saw a significantly greater decrease in reported delayed-onset muscle soreness compared with women (p < .01). This study also showed a reverse correlation between the reduction in delayed-onset muscle soreness and the restoration of power output after exercise-induced muscle damage in men, but no such correlation was found in women. However, the small sample size (n = 10 F, 10 M) and variance related to interindividual differences in hormone levels may have contributed to the lack of detectable correlation in women.
So is caffeine beneficial to female athletes? Can caffeine boost performance of of female athletes and is is safe for women? Research is still needed but the most likely the answer to all three questions is yes; performance benefits of caffeine can be experienced doses ranging from 3-6mg/kg body weight. These benefits may vary depending on the performance outcomes being measured, training status, and individual responses based on genetics. However, far more research is needed to conclude whether the caffeine benefits seen in women are consistent across the menstrual cycle, use of varying hormonal contraceptives, or as women age and experience perimenopause and menopause.
Now you may be wondering, what exactly does 3-6mg/kg look like, and is that possible to consume through whole foods, coffee, or do female athletes need caffeine supplements? For a 150 pound person, 3-6mg/kg looks like approximately 200mg-400mg. To answer your questions, you’ll want to take a look at my upcoming blogs - top 6 sports nutrition products with caffeine as well as my favorite caffeine-filled recipes to fuel your day! Stay tuned!
REFERENCES:
https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/the-buzz-on-energy-drinks#:~:text=About%2090%25%20of%20adults%20consume,and%20young%20adults%2C%20behind%20multivitamins.
Murphy MJ, Rushing BR, Sumner SJ, Hackney AC. Dietary Supplements for Athletic Performance in Women: Beta-Alanine, Caffeine, and Nitrate. Int J Sport Nutr Exerc Metab. 2022 Feb 23;32(4):311-323. doi: 10.1123/ijsnem.2021-0176. PMID: 35196646.
Maughan RJ, Burke LM, Dvorak J, et alIOC consensus statement: dietary supplements and the high-performance athleteBritish Journal of Sports Medicine 2018;52:439-455.
Murphy MJ, Rushing BR, Sumner SJ, Hackney AC. Dietary Supplements for Athletic Performance in Women: Beta-Alanine, Caffeine, and Nitrate. Int J Sport Nutr Exerc Metab. 2022 Feb 23;32(4):311-323. doi: 10.1123/ijsnem.2021-0176. PMID: 35196646.
Guest, N. S., VanDusseldorp, T. A., Nelson, M. T., Grgic, J., Schoenfeld, B. J., Jenkins, N. D. M., … Campbell, B. I. (2021). International society of sports nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 18(1). https://doi.org/10.1186/s12970-020-00383-4