What high-quality prospective studies exist on sexual behavior and prostate cancer risk?

1. The flagship prospective cohort: Health Professionals Follow‑up Study and its updates

A large, long-term prospective analysis from the Health Professionals Follow‑up Study—updated with an additional decade of follow‑up—reported that men who reported more frequent ejaculation in adulthood had a lower risk of total prostate cancer incidence, framing ejaculation frequency as a potentially modifiable factor worth further research ^[1]; this result was summarized for lay readers in a Harvard Health overview that highlighted a roughly 31% lower risk among men reporting 21+ ejaculations per month versus 4–7 per month in some analyses ^[2].

2. Other prospective work and narrative syntheses: a mixed but cautiously consistent signal

Narrative and systematic reviews that explicitly searched for prospective studies find a mixed but suggestive picture: recent reviews identified several prospective cohort studies among the small set of total investigations and emphasize discordant findings across designs, concluding that higher ejaculation frequency often trends toward a protective association but that uncertainty remains ^[3]; these reviews note six prospective studies surfaced in broad searches alongside multiple case‑control reports ^[3].

3. What meta‑analyses say when you combine designs

Dose‑response meta‑analyses and pooled studies that mix prospective cohorts with many case‑control reports have reported varied associations: one 2018 dose–response meta‑analysis concluded that more female sexual partners and earlier age at first intercourse were associated with increased prostate cancer risk, while ejaculation frequency showed no clear linear association though moderate frequency might be protective ^{[4] [5]}. These syntheses often include few true prospective cohorts and therefore inherit biases from retrospective designs ^{[4] [5]}.

4. The STI angle: consistent signal from older meta‑analyses and case–control work

Separate meta‑analytic work has repeatedly found an elevated relative risk of prostate cancer among men with histories of sexually transmitted infections—syphilis and gonorrhea feature in several pooled analyses—suggesting an infectious or inflammatory pathway as a plausible mechanism ^[6]. Population‑based case–control investigations that collected sexual behavior and serologic data likewise flagged associations between unprotected sex, encounters with sex workers, specific STIs, and higher prostate cancer risk ^{[7] [8]}.

5. Methodological limits that temper certainty

Across the literature the dominant limitations are clear and repeatedly noted: many studies are case–control (subject to recall and selection bias) rather than prospective ^{[4] [5]}, measurement of sexual behavior and ejaculation frequency is self‑reported and variable across instruments ^[9], and confounding (age, screening/PSA testing patterns, urinary health, hormones, and lifestyle) complicates inference—reviews explicitly call for larger, well‑conducted prospective cohorts with standardized exposure measures to resolve contradictions ^{[3] [9]}.

6. Bottom line and where research should go

The highest‑quality prospective evidence to date—chiefly the Health Professionals Follow‑up Study and its updated analyses—supports an inverse association between higher ejaculation frequency and total prostate cancer risk, but this finding is not uniformly replicated and coexists with meta‑analytic signals implicating STIs and some sexual‑behavior measures in increased risk ^{[1] [2] [6] [4]}. Consensus statements in recent reviews call for further prospective cohorts, harmonized exposure metrics, and attention to screening bias and infection history before clinical recommendations can be made ^{[3] [9]}.