One of the reasons it’s difficult to know for certain if caffeine affects fertility is due to the quality of studies which have been done, that the results of the studies have been conflicting and that not many studies have actually looked at women who are experiencing trouble conceiving. To add to the confusion is that it isn’t clear exactly why caffeine affects fertility but it’s thought it may alter hormone levels, therefore, affecting ovulation and corpus luteum functioning (which is required for successful implantation of the embryo).
Of the evidence we do have there is a study in which women recorded their caffeine consumption whilst trying to get pregnant and this study found that those who consumed less than one cup of coffee per day were twice as likely to get pregnant per cycle (1). Another study involving women who were using IVF and other fertility treatments found caffeine consumption was a risk factor for not achieving a live birth (2). Which means either those women who consumed caffeine were either less likely to become pregnant in the first place or more likely to experience a miscarriage. This study found that this was related to ‘usual’ caffeine consumption and recommended women reduce their caffeine intake prior to their IVF cycle, not just when they start them.
So how much caffeine is in a cup of coffee? Well it depends on what sort of coffee it is, decaf is very low (3mg), instant is next (60-80mg) and then coffee shop coffees are going to be higher (113-282mg in a small coffee). Levels in tea vary depending on how long you brew it for and also on the type of tea with black tea (25-100mg) being higher in caffeine than green tea (30-50mg). Coke and other cola drinks vary but levels should be listed on the can (36-48mg) and same goes for energy drinks (80mg). Luckily, chocolate is pretty low at about 20mg in a 100gm bar of milk chocolate (3).
In short, the hard evidence isn’t in but it would be safe to conclude that caffeine adversely affects fertility in a dose-dependent way. So generally, good advice would be that women who are experiencing difficulty becoming pregnant should limit their coffee intake to 1 cup or to less than 200mg of caffeine per day.
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1. Wilcox, A., Weinberg, C. et al. (1997). “Caffeinated beverages and decreased fertility.” Lancet 2(8626-8627): 1453-1456.
2. Klonof-Cohen, H., Bleha, J. & Lam-Kruglick, P. (2002). ‘A prospective study of the effects of female and male caffeine consumption on the reproductive endpoints of IVF and gamete intra-Fallopian transfer.’ Human Reproduction 17(7): 1746-1754.
3. The Australian Beverage Council. ”Caffeine – The Facts”. www.australianbeverages.org/for-consumers/caffeine-facts/, (Accessed 29th August 2014).