Is L. reuteri Safe for Male Fertility?
There is no evidence that Lactobacillus reuteri negatively affects male fertility, and it can be considered safe for men to take. The available research on L. reuteri focuses exclusively on its antimicrobial and gastrointestinal benefits, with no studies documenting adverse effects on sperm parameters or reproductive function 1, 2, 3.
Evidence Review
What We Know About L. reuteri
- L. reuteri is a naturally occurring probiotic that colonizes the human gastrointestinal tract and has demonstrated safety in clinical trials for treating acute diarrhea and preventing antibiotic-associated diarrhea 1, 2
- Studies have used doses ranging from 10^10 to 10^11 colony-forming units daily without reporting reproductive adverse effects 1, 2
- The probiotic produces antimicrobial compounds like reuterin that target enteric pathogens but has not been associated with hormonal disruption or testicular toxicity 3
Probiotics and Male Fertility: The Broader Context
- Emerging evidence actually suggests potential benefits: One randomized controlled trial of 56 men with idiopathic infertility showed that prebiotic/probiotic supplementation significantly increased sperm concentration, motility, normal morphology, and DNA integrity compared to placebo 4, 5
- The European Association of Urology guidelines acknowledge that probiotic interventions may improve sperm parameters, though more research is needed 4
What Actually Harms Male Fertility
The major guideline-supported risk factors for male infertility include:
- Obesity: Strong evidence links elevated BMI with impaired reproductive function and abnormal semen parameters 6
- Smoking: Moderate evidence suggests negative effects on semen quality, and cessation is strongly recommended 6
- Recreational drugs: Men attempting to conceive should completely abstain from marijuana/THC, which demonstrates detrimental effects on sperm quality 7
- Testosterone therapy: Absolutely contraindicated in men seeking fertility as it suppresses spermatogenesis and causes azoospermia 4, 5
- Heat exposure: Though evidence quality is limited, excessive heat may impair spermatogenesis 6
Clinical Bottom Line
L. reuteri poses no documented risk to male fertility and may theoretically provide benefits through probiotic mechanisms. The absence of any reported reproductive toxicity across multiple clinical trials, combined with emerging evidence that probiotics can improve sperm parameters, supports its safety profile 4, 1, 2.
Key Caveats
- No studies have specifically evaluated L. reuteri's direct effects on semen analysis parameters or fertility outcomes, so definitive benefit cannot be claimed 1, 2, 3
- Men with fertility concerns should prioritize evidence-based interventions: weight loss if obese, smoking cessation, avoiding recreational drugs, and regular physical exercise 6, 4, 5
- Any supplement intervention requires at least 74 days (the duration of spermatogenesis) to show potential effects on sperm quality 5