CAFFEINE INTAKE AND FECUNDABILITY - A FOLLOW-UP-STUDY AMONG 430 DANISH COUPLES PLANNING THEIR FIRST PREGNANCY

Fecundability has been defined as the ability to achieve a recognized pregnancy. Several studies on caffeine and fecundability have been con ducted but have been inconclusive. This may be explained partly by lac k of stratification by smoking. Furthermore, few researchers have trie d to separate the effect of caffeine from different sources (coffee, t ea, cola, and chocolate), Clearly, the relationship between caffeine a nd fecundability needs further research, given the high prevalence of caffeine intake among women of childbearing age, We examined the indep endent and combined effects of smoking and caffeine intake from differ ent sources on the probability of conception. From 1992 to 1995, a tot al of 430 couples were recruited after a nationwide mailing of a perso nal letter to 52,255 trade union members who were 20 to 35 years old, lived with a partner, and had no previous reproductive experience. At enrollment and in six cycles of follow-up, both partners filled out a questionnaire on different factors including smoking habits and their intake of coffee, tea, chocolate, cola beverages, and chocolate bars. In all, 1596 cycles and 423 couples were included in the analyses, The cycle-specific association between caffeine intake and fecundability was analyzed in a logistic regression model with the outcome at each c ycle (pregnant or not pregnant) in a Cox discrete model calculating th e fecundability odds-ratio (FR), Compared to nonsmoking women with caf feine intake less than 300 mg/d, nonsmoking women who consumed 300 to 700 mg/d caffeine had a FR of 0.88 [95 % confidence interval (CI) 0.60 -1.31], whereas women with a higher caffeine intake had a FR = 0.63 (9 5% CI 0.25-1.60) after adjusting for female body mass index and alcoho l intake, diseases of the female reproductive organs, semen quality, a nd duration of menstrual cycle. No dose-response relationship was foun d among smokers. Among males, the same decline in point estimates of t he FR was present, Smoking women whose only source of caffeine was cof fee (>300 mg/d) had a reduced fecundability odds-ratio (FR = 0.34; 95% CI 0.12-0.98), An interaction between caffeine and smoking is biologi cally plausible, and the lack of effect among smokers may be due to fa ster metabolism of caffeine, Our findings suggest that especially nons moking women who wish to achieve a pregnancy might benefit from a redu ced caffeine intake. (C) 1998 Elsevier Science Inc.