The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Caffeine, a natural alkaloid found in tea, coffee, cocoa, and cola, was tested for its effects on reproduction and fertility in Swiss CD-1 mice. Caffeine was tested simultaneously at two laboratories, each using a variation on the standard RACB study design. This study performed Tasks 1, 2, and 3, while the other study in mice performed Tasks 1, 2, and 4. Caffeine was among the very first compounds run at these labs using this protocol. Data on body weights, clinical signs, and food and water consumptions were collected during the dose-range-finding phase (Task 1), and used to set exposure concentrations for Task 2 at 0.0, 0.012, 0.025, and 0.05% in drinking water. Water was chosen to mimic the route of human exposure. Water consumption was not affected by addition of caffeine. These levels of caffeine, and measured water consumption and body weights, produced calculated consumption estimates nearly equal to 22, 49, and 93 mg/kg/d. Three control, 1 low dose, and 1 middle dose mouse died during the study. Treated mice were also reported to have lost facial hair, but the percentages and groups involved were not specified.
There was no effect on the mean number of litters/pair produced, or on the aggregate mean number of pups/litter (the total number of pups/total number of litters for all pairs at a treatment level). There was a 20% reduction in live male pups/litter, however. Evaluating each litter individually, after the first litter, the high dose group always delivered 1-2 pups less than the controls; at the fifth litter, the controls delivered a mean of 10.3 ± 7 pups (mean ± SEM), while the high dose group delivered a mean of 8.6 ± 1 pups. The proportion of pups born alive was reduced by 3%, 5%, and 5% in the low, middle and high dose groups, respectively. Additionally, pup body weight adjusted for litter size was reduced by 4% at the high dose.
A crossover mating trial (Task 3) was performed. There were no differences between the groups in the mating and fertility indices, and no differences with respect to pup number or viability or weight.
Task 4 was not performed on this study. After 7 days of vaginal smears to evaluate cyclicity, the control and high dose Task 2 mice were killed and necropsied. Female body weight at necropsy was reduced by 5%, while body-weight-adjusted organ weights were unchanged. Ante-mortem vaginal cyclicity was unaffected by caffeine exposure. Male body weight was unchanged by consumption of 0.05% caffeine, but adjusted liver weight was increased by 10%. Absolute testis weight dropped by 7% and adjusted seminal vesicles weight decreased by 12%. Sperm motility values for controls was low (47% motile), so the 21% reduction in the treated group should be viewed with caution. Similarly, the control epididymal sperm density was nearly equal to half of the subsequent control values for this lab, so the significant increase in sperm density in the caffeine-treated group is likely erroneous.
The slight but significant reductions in (male) pup number, pup viability, and adjusted pup weight suggest that caffeine produced some slight reproductive toxicity. This occured in the presence of very slight indications of other toxicities (body or organ weight changes).