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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
 Figà-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 = 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
  1. BMI body mass index, OR odds ratio, RR risk ratio, CI confidence interval, FR fecundability ratio, MSOME Motile Sperm Organelle Morphology Examination