Table 2 Estimates of coffe/caffeine consumption, outcomes reported and confounding factors in the selected studies
From: Coffee and caffeine intake and male infertility: a systematic review
First author, year | Estimates of caffeine (mg/serving) | Main findings | Confounding factors |
|---|---|---|---|
Full text | |||
 Cole, 2006 [34] | Not reported Caffeine drinks per month | Higher reported caffeine consumption was consistently, although not significantly, associated with longer time to pregnancy for both parents and the couple overall. | Intercourse frequency, mercury in blood |
 Curtis, 1997 [27] | coffee = 100 tea = 50 cola = 40 Level of daily intake | A slight decrease in fecundability among men was found when caffeine drinkers were compared with complete abstainers. Low (≤100 mg caffeine per day) versus high (>100 mg caffeine per day) consumption was also examined; no association with fecundability was observed using this cut-point. Consuming >3 cups of tea per day was associated with decreased fecundability. | Smoking, recent OC use, woman’s caffeine and age |
 FigĂ -Talamanca, 1996 [26] | Not estimated Cups of coffee per day | No consistent association between coffee consumption and sperm count, motility, morphology. High prevalence of atypical forms was observed among men drinking 1-3 cups of coffee/day, but not among those drinking >3. | Age, smoking and alcohol |
 Florack, 1994 [25] | coffee = 100 tea = 50 cola (375 ml) = 40 Level of daily intake | Heavy caffeine intake (>700 mg/day) among partners was negatively related to fecundability when compared with the lowest intake level (OR adjusted = 0.6, 95% CI, 0.3-0.97). | Smoking and alcohol, woman’s caffeine intake |
 Horak, 2003 [32] | Not estimated mL of coffee per day | No correlation between alcohol or coffee consumption and sperm DNA adducts | None |
 Jensen, 1998 [30] | coffee = 100 tea = 50 cola (100 ml) = 100 chocolate drink = 25 chocolate bar = 12.5 Level of daily intake | No adverse effect of caffeine among male smokers. Among nonsmokers, intake of more than 700 mg/d caffeine was associated with a Fecundability Ratio of 0.47 (95% CI 0.26–0.82) among males compared with nonsmokers whose daily caffeine intake was 0 to 299 mg/d. Among nonsmokers, we found no statistically significant associations between fecundability and intake of any specific source of caffeine, but a similar tendency was found for each source as for overall caffeine intake. | M and F: smoking, reproductive organs diseases, alcohol intake, age, BMI M: sperm concentration F: duration of menstrual cycle, use of OC as last method of birth control |
 Jensen, 2010 [38] | coffee = 117 tea = 70 cola (500 ml) = 70 chocolate drink = 5 chocolate bar = 7 Level of daily intake | 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. Semen volume, sperm concentration, total sperm count, and percentage of spermatozoa with normal morphology decreased among cola-drinking men compared with nondrinkers. | Fever >38C within the last 3 months, period of abstinence, BMI, in utero exposure to smoking, conditions found at the physical examinations, self-reported genital conditions, cryptorchidism |
 Jurewicz, 2014 [40] | Not estimated Days of coffee drinking/week | A positive relationship was found between coffee drinking everyday and the lack of chromosome X or Y, as well as coffee drinking 1–6 times per week and additional chromosome 18. | abstinence, age and past diseases |
 Klonoff-Cohen, 2002 [31] | coffee = 100 tea = 50 soda (can) = 100 chocolate drink = 4 chocolate bar = 7-18 (milk-dark) Level of daily intake | Male caffeine consumption had no relation with semen parameters, clinical pregnancy or achieving a livebirth. Analysed as a linear continuous predictor, was a significant risk factor for multiple gestation: OR = 2.2 (95% CI 1.1-4.4) and OR = 3.0 (95% CI 1.2-7.4) for men who increased their usual intake or intake during the week of initial visit by 100 mg/day. | Smoking, alcohol, years of schooling, partner’s age, race, indication to ART, number of attempt. |
 Kobeissi, 2007 | Not estimated Cups of coffee per day | Cases had a slightly higher mean intake of coffee (cups/day 3.2 ± 4.7 vs 2.9 ± 4.7, p = 0.574). At the multivariate analisys, odds of caffeine intake for being infertile were 1.05 (95% CI 0.96-1.14 by 1 cup/day). | Family history of infertility, reproductive health index, smoking, soft drinks intake, occupational exposures, war exposure |
 Marshburn, 1989 [22] | Not estimated Cups of coffee per day | Coffee drinking was correlated with increases in sperm density and percentage of abnormal forms. Among non smokers, coffee drinkers had a higher percentage of motile sperm as compared to non-coffee drinkers. | Alcohol, smoking |
 Oldereid, 1992 [23] | Not estimated Cups of coffee per day | No relationship could be established between sperm concentration, motility and morphology, and the number of cups of coffee drank daily | None |
 Parazzini, 1993 [24] | Not estimated Cups of coffee per day | Adjusted rate ratios for dyspermia were significantly higher in men drinking 2-3 and ≥4 cups/day (reference 0-1), compared either to normospermic men (1.8 and 3.0 respectively) or men of unknown semen quality (RR 1.3 and 4.2 respectively). | Age, education, smoking, alcohol |
 Radwan, 2016 [42] | Not estimated Days of coffee drinking/week | Coffee drinking were not related with any of the examined parameters of sperm DNA damage and high DNA stainability | age, smoking, alcohol, past diseases, BMI, duration of couple’s infertility, abstinence, level of stress, cell phone use |
 Ramlau-Hansen, 2008 [37] | coffee = 100 tea = 50 cola (500 ml) = 50 Level of daily intake | Caffeine exposure did not seem to affect adversely the semen quality or the levels of inhibin B or FSH. No association between caffeine and sperm motility or morphology. Men with a high caffeine intake had about 14% higher concentration of testosterone than men with a low caffeine intake. | abstinence time, diseases of the reproductive organs, smoking, season, maternal smoking during pregnancy |
 Robbins, 1997 [29] | Equivalent of 8 oz. cup: Tea = 0.5*n Cola = 0.25*n Level of daily intake | No difference between groups (0, 1 or ≥2 cups/day) was observed in term of semen motility and morphology. Lower density was found in the light caffeine group. Caffeine was significantly associated with increased frequencies of sperm aneuploidy XX18 and XY18, diploidy XY18-18 and the duplication phenotype YY18-18 | Age, smoking, alcohol |
 Schmid, 2007 [35] | Equivalent of 8 oz. cup: Tea = 0.5*n Cola = 0.25*n Level of daily intake | In tertiles of caffeine consumption, men with >308 mg of caffeine intake per day (equivalent to ∼ 2.9 cups of coffee) had ∼ 20% higher neutral % tail DNA than men with no caffeine intake (P = 0.01 unadjusted; P = 0.005 after adjusting for the covariates total kilocalorie intake and the history of urinary tract infections) | Vitamin C use, season, Kilocalories, urinary tract infections |
 Sobreiro, 2005 [33] | Not estimated Cups of coffee per day | Among patients not drinking coffee, progressive motility averaged 57.1%, whereas for the patients who consumed more than six cups of coffee per day, it averaged 62.4% (p for trend < 0.05). There were no significant differences in semen volume, sperm concentration or sperm morphology. | None |
 Vine, 1997 [28] | Equivalent of 8 oz. cup: Tea = 0.5*n Cola = 0.25*n Level of daily intake | No convincing evidence was found for associations between the means, standard deviations, or skewness of any of nine sperm nuclear morphometric parameters and caffeine exposure | Age, smoking, alcohol |
 Wesselink, 2016 [43] | Coffee = 135 Decaf.coffee = 5.4 Black tea = 40 Green tea = 20 White tea = 15 Soda = 23-69 Energy drinks = 48-280 Level of daily intake | Total caffeine intake among males was associated with fecundability (FR for ≥300 vs. <100 mg/day caffeine among males = 0.72, 95% CI = 0.54–0.96), although the association was not monotonic. With respect to individual beverages, caffeinated soda and energy drink intake were associated with reduced fecundability among males. | Age, ethnicity, education, smoking, alcohol, intercourse frequency, sleep duration, work time, partner’s caffeine intake |
 Wogatzky, 2012 [39] | Not estimated Cups of coffee per day | 204 men out of 1321 drinking coffee had an intake of more than 3 cups of coffee per day. With respect to MSOME criteria, these patients revealed a marked tendency towards lower sperm quality. | None |
 Yang, 2015 [41] | Not estimated Cups of coffee per day | Coffee consumption was found to be associated with increased progressive and nonprogressive motility of 8.9% or 15.4% for subjects consuming 1–2 cups/wk or 3 cups/wk of coffee, respectively. Cola consumption appeared an association with decreased semen volume at 4.1% or 12.5% for 1–2 bottles/wk or 3 bottles/wk. | age, tobacco and alcohol consumption, duration of abstinence, BMI, coffee/cola/fried food/baked foods consumption |
Published or only accessible as abstract | |||
 Adelusi, 1998 [44] | Not reported | Frequent coffee drinking associated to higher sperm motility | n.d. |
 Al-Inany, 2001 [45] | Not reported | No association between coffee consumption and sperm parameters | n.d. |
 Belloc, 2013 [46] | Not reported | Among caffeine consumers, semen volume was slightly higher (3.2 ± 1.6 vs. 3.1 ± 1.6 ml, p < 0.01) as pH (p < 0.01), but concentration was lower (60.0 ± 90.7 vs. 69.6 ± 124.9 millions/ml, p < 0.01), azoospermia less frequent (2.7 vs. 4.4%, p < 0.01). No relationship was observed for motility and morphology, nor for DNA fragmentation and chromatin decondensation. In a multivariate model including age, results were confirmed for volume (p < 0.01), but not for concentration. Caffeine intake was associated with a lower risk of elevated fragmentation (OR = 0.92, 95% CI 0.92-0.99). | n.d. |
 Karmon, 2013 [47] | Not reported | Caffeine intake was not related to semen quality parameters | Alcohol, smoking |
 Karmon, 2014 [48] | Not reported | Male caffeine intake was negatively associated with clinical pregnancy per initiated cycle. Compared to men consuming <88 mg/day of caffeine, adjusted odds ratios (95% CI) for clinical pregnancy per initiated cycle were 1.4 (0.5-3.8), 1.7 (0.6-4.8), and 0.4 (0.1-1.0) for men consuming 88-168 mg/day, 169-264 mg/day, and ≥265 mg/day of caffeine, respectively. | Alcohol, smoking |
 Pecoraro, 2015 [49] | Not reported | Fewer fertile than infertile men were coffee drinkers (p = 0.003) | None |