Study Title and Description
Caffeine intake and semen quality in a population of 2,554 young Danish men.
Key Questions Addressed
|1||For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on reproductive and developmental outcomes?|
Primary Publication Information
|Title||Caffeine intake and semen quality in a population of 2,554 young Danish men.|
|Author||TK Jensen,SH Swan,NE Skakkebaek,S Rasmussen,N Jørgensen,|
Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Reproductive Toxicity - Design Details
No arms have been defined in this extraction form.
|Question... Follow Up||Answer||Follow-up Answer|
|What outcome is being evaluated in this paper?||Reproductive and Development|
|What is the objective of the study (as reported by the authors)?||The authors examined the association between semen quality and caffeine intake among 2,554 young Danish men recruited when they were examined to determine their fitness for military service in 2001–2005.|
|Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods)||Population: Men recruited from September 2001 to December 2006 from the men in the military draft; these men completed a questionnaire which included detailed information about lifestyle factors. Participants delivered a semen sample, had a blood sample drawn, and underwent a physical examination. Participants did not differ from nonparticipants with regard to age, but they were better educated than nonparticipants (data not shown). Semen analysis: All men provided a semen sample. The period of ejaculation abstinence was recorded, and the semen sample was analyzed according to the World Health Organization’s 1999 guidelines, modified in accordance with Jørgensen et al. The current analysis includes morphology results for only a subset of men because not all samples had been counted yet. Spermatozoa morphology was assessed in 284 for the 299 men consuming more than 1 bottle (0.5 L) of cola per day, as well as for 97 randomly selected men consuming no cola and 98 randomly selected men consuming less than 1 bottle (0.5 L) of cola per day because we initially found a negative association between cola intake and semen quality. Questionnaire: Participants completed a questionnaire containing information regarding: diseases, born with testicles in scrotum, fever, parents’ social class, dietary habits, and beverage consumption. Participants were asked, How much did you consume of the following beverages during the last week? Possible responses were as follows: glasses of wine (units), bottles of beer (0.33 L), number of strong alcoholic drinks (12 cL), bottles of cola (0.5 L), bottles of diet soft drinks (0.5 L), and number of chocolate bars (50 g). In addition, they were asked how many cups of coffee, tea, and chocolate containing beverages they consumed daily during the last week. Each man’s daily caffeine intake was estimated by assuming a cup to contain 150 mL and the caffeine content to be 117 mg in one cup of coffee, 70 mg in one cup of tea, 5 mg in one cup of chocolate beverages, 70 mg in 0.5 L of cola and diet soft drinks, and 7 mg in a 50-g chocolate bar (1). In the analyses, ‘‘weekly intake of cola’’ was calculated as the sum of reported drinks of cola and diet soft drinks (assuming diet soft drinks to be cola). Statistics: Outcome variables were semen volume, sperm concentration, total sperm count, and percentages of motile and morphologically normal spermatozoa. Exposure variables were average daily caffeine intake included as a continuous variable and categorized as daily intake of 0–100 mg, 101–200 mg, 201–800 mg (1–800 mg), and > 800 mg, which corresponds to approximately 1, 2–7, and > 7 cups of coffee per day. All analyses were initially performed with total daily caffeine consumption and then for men who reported caffeine intake from coffee, tea, chocolate beverages or bars, diet soft drinks, or cola separately to determine the independent associations with each. Cola consumption was reported as weekly intake of number of 0.5-L bottles; cola intake was entered as a continuous variable or categorized as no cola, 1–7, 8–14, and > 14 bottles per week. Semen quality in relation to caffeine and cola intake by the Kruskal-Wallis test. Then, the distributions of the variables from the questionnaires and physical were compared via chi-square test to identify potential confounders. Finally, data were examined by using univariate analyses of variance. Covariates initially included factors possibly associated with semen parameters or caffeine consumption and were then excluded stepwise if they did not change the estimate by more than 10%. Analyses for different types of caffeine intake were performed by including the sources in separate models as well as by simultaneously including all caffeine-containing sources in the same model.|
|How many outcome-specific endpoints are evaluated?||5|
|What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)||semen volume|
|List additional health endpoints (separately).|
|List additional health endpoints (separately)|
|What is the study design?||Cross-sectional|
|Randomized or Non-Randomized?|
|What were the diagnostics or methods used to measure the outcome?||Objective|
|Optional: Name of Method or short description|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||Daily caffeine intake included as a continuous variable and categorized as daily intake of 0–100 mg, 101–200 mg, 201–800 mg (1–800 mg), and > 800 mg.|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)||diseases (various, combined), born with testicles in scrotum, fever, parents’ social class, dietary habits, and beverage consumption|
|Provide a general description of results (as reported by the authors).||Men who reported no caffeine intake had better semen quality (median sperm concentration, total sperm count, and morphological normal sperm; however, moderate consumption of caffeine was not associated with a reduction in semen quality. Men with a high caffeine intake (> 800 mg of caffeine per day) had a slight reduction in semen quality (not statistically significant). After control for confounders, low (101–200 mg) to moderate (201–800 mg) daily caffeine consumption was not associated with a reduction in semen quality. Consumption of > 800 mg of caffeine per day resulted in a nonsignificant reduction in semen quality. Over the entire range, only semen volume decreased significantly with increasing caffeine intake. Analyses from different sources, after controlling for confounders, resulted in no association of coffee, tea, chocolate beverages or bars, or diet soft drinks with semen quality. When all caffeine sources were included simultaneously in the model, only cola consumption was associated with a significant reduction in semen quality. The analyses were repeated for caffeine intake from sources other than cola (Table 4) to determine whether the association between caffeine and semen quality was attributable to an adverse effect of cola. The same magnitude of effect as for total caffeine intake was found for men whose caffeine intake was not derived from cola. Authors also examined associations of caffeine and cola consumption with serum reproductive hormones (testosterone, inhibin B, follicle-stimulating hormone, and luteinizing hormone). However, we found no statistically significant associations (data not shown).|
|Did the authors perform a dose-response analysis (or trend/related analysis)?||Yes|
|What were the authors's observations re: trend analysis?||Over the entire range, only semen volume decreased significantly with increasing caffeine intake.|
|What were the author's conclusions?||Moderate caffeine intake (101–800 mg/day) compared with low intake (<100 mg/day) was not associated with semen quality. High caffeine (>800 mg/day) intake was non-significantly associated with reduced sperm concentration and total sperm count. The authors cannot exclude the possibility of a threshold above which cola, and possibly caffeine, negatively affects semen quality. Alternatively, the less healthy lifestyle of these men may explain these findings.|
|What were the sources of funding?||This work was supported by the European Union (contract QLK4-1999-01422/BMH4-CT96-0314), Danish Environmental Agency, Danish Research Council (grants 2107-04-0006, 22-03-0198, and 95-103-21990), Malermester Johansens Fond and Svend Andersens Fond, and The Danish Agency for Science, Technology and Innovation (grant 271070678).|
|What conflicts of interest were reported?||Conflict of interest: none declared.|
|Does the exposure (dose) need to be standardized to the SR?||Multiple metrics|
|Provide calculations/conversions for the exposure based on the decision tree in the guide (for all endpoints/exposure levels of interest).||Only caffeine-based analyses used in comparisons.|
|List all the endpoint(s) followed by the dose (mg) which will be used in comparison to Nawrot. Characterize value as LOAEL/NOAEL, etc. if possible.||>800 NOEL semen volume >800 NOEL sperm concentration >800 NOEL total sperm count >800 NOEL % motile sperm >800 NOEL % morphologically normal forms|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||Selected caffeine-based analyses as most refined Endpoints collectively described by authors as semen quality No data shown for associations of caffeine and cola consumption with serum reproductive hormones (testosterone, inhibin B, follicle-stimulating hormone, and luteinizing hormone).|
|What is the importance of the study with respect to the adverseness of the outcome?||Important|
No baseline characteristics have been defined for this extraction form.
Results & Comparisons
No Results found.
|Arm or Total||Title||Description||Comments|
No quality dimensions were specified.
No quality rating data was found.