Studies assessing the impact of caffeine on fertility have evaluated a variety of outcomes including time to pregnancy, infertility and semen quality6-10.
Incorrect, or imprecise, assessments of the duration of exposure are a primary concern for the few studies addressing time to conception and ovulatory infertility8,9. Potential recall bias and exposure misclassification may explain the modest association reported for coffee and tea consumption and increased time to pregnancy.
A Danish prospective study evaluated the relation of caffeine, coffee, tea and sodas with time to pregnancy in a cohort of 3,628 women planning a pregnancy. There was little relation between fecundability and caffeine intake of more than 300mg per day compared with less than 100 mg/day or coffee intake of 3 or more servings a day compared with none8.
No support for an association with infertility due to ovulation disorders was provided, but exposure measurement error was likely introduced as a result of the timing of exposure assessments8,9.
Additionally, a 2018 population-based cohort study found no association between coffee, tea or total caffeine consumption and the risk of primary infertility in women10.
Evaluations of semen quality have consistently failed to observe adverse effects associated with caffeine intake1, as suggested by a Danish study6. However, a systematic literature review including 19,697 men concluded that whilst the literature suggests that caffeine intake, possibly through sperm DNA damage, may negatively affect male reproductive function, data from epidemiological studies on semen parameters and fertility is inconsistent and inconclusive7.
As stated by an Australian review paper, research results are unclear and insufficient to provide coffee consumption guidelines for preconception advice9.
In summary, consistent relationships between caffeine intake and measures of sub-fecundity have not been observed.