在全台灣男性十大癌症發生率中，攝護腺癌佔第五名，增加比率逐年上升。而在2017年的癌症登記報告中，全台灣男性一年發生攝護腺癌的總數為5866人，約佔男性新發生癌症的10% (註：全世界每年新發生癌症的15%是攝護腺癌)。雖然大約知道飲食和運動可以次級預防，但是如何預防攝護腺癌還是缺乏實證，而且大部分的危險因子都是不能自己控制的，例如：年紀、人種、家族史、或者基因。這篇前瞻性的研究來自美國哈佛醫學院，自1986年起針對健康產業的專家 (其中91%是白人，有醫師、藥師、護理師、來自醫學院的教授…)等沒有癌症的自願者，組成一個可以持續追蹤分析的資料來研究 (Health Professional Follow-up Study, HPFS)。這群受試者每兩年就會接受一次問卷分析，而在1992年在問卷中加入射精頻率的選項；初步追蹤8年 (到2000年)，相較於每月射精4-7次的族群，每月射精21次以上的族群，發生攝護腺癌的機率少了50%。而這篇是為了更確立這個發現，於是多加了10年的追蹤時間 (共追蹤了18年的時間，到2010年)，所做的研究更新。

研究結果發現，在年齡20-29歲的組別裡，每月射精21次以上比起每月射精4-7次，可以減少19%攝護腺癌發生。而在年齡40-49歲的組別裡，每月射精21次以上比起每月射精4-7次，可以減少22%攝護腺癌發生。在年齡20-29歲的組別裡，每月射精21次以上的族群，統計出每1000人年會發生6.56個攝護腺癌；每月射精4-7次的族群，統計出每1000人年會發生8.95個攝護腺癌 (兩者每1000人年相差 2.39個)。而在年齡40-49歲的組別裡，每月射精21次以上的族群，統計出每1000人年會發生6.74個攝護腺癌；每月射精4-7次的族群，統計出每1000人年會發生8.94個攝護腺癌 (兩者每1000人年相差 2.20個)。

但是射精次數的多寡，也與BMI、身體活動、飲食、暴露在性病感染風險程度息息相關，而這些因素也是可能跟攝護腺癌與它的進展可能有關的因子。不過這篇研究最重要的，是發現射精次數跟”低風險”攝護腺癌發生的機率呈負相關。這也意味著說，針對性生活教活躍的族群，也許可以減少攝護腺癌的篩檢與追蹤 (註：性功能/性慾減低也是攝護腺癌治療最主要的副作用之一)。另外，增加射精次數到底為何可以預防攝護腺癌的發生 (也許跟射精時候可以影響周邊區的上皮細胞阻礙了檸檬酸的氧化製造、也許跟射精可以減少攝護腺管內的晶體製造、也許跟射精可以減少身心壓力和中樞神經系統的抑制而進而減少攝護腺上皮細胞轉化成癌細胞有關)，本篇無法提供一個結論，還需要進一步的分析研究。最後，還是需要台灣本土或者亞洲區域的類似研究分析，才能把本篇的射精可能減少攝護腺癌發生的結論確立。

Background: Evidence suggests that ejaculation frequency may be inversely related to the risk of prostate cancer (PCa), a disease for which few modifiable risk factors have been identified.

Objective: To incorporate an additional 10 yr of follow-up into an original analysis and to comprehensivelyevaluatetheassociationbetweenejaculationfrequencyandPCa,accountingfor screening, clinically relevant disease subgroups, and the impact of mortality from other causes.

Design, setting, and participants: A prospective cohort study of participants in the Health Professionals Follow-up Study utilizing self-reported data on average monthly ejaculation frequency. The study includes 31 925 men who answered questions on ejaculation frequency on a 1992 questionnaire and followed through to 2010. The average monthly ejaculation frequency was assessed at three time points: age 20–29 yr, age 40–49 yr, and the year before questionnaire distribution.

Outcome measurements and statistical analysis: Incidence of total PCa and clinically relevant disease subgroups. Cox models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

Results and limitations: During 480 831 person-years, 3839 men were diagnosed with PCa. Ejaculation frequency at age 40–49 yr was positively associated with age-standardized body mass index, physical activity, divorce, history of sexually transmitted infections, and consumption of total calories and alcohol. Prostate-specific antigen(PSA) test utilization by 2008, number of PSA tests, and frequency of prostate biopsy were similar across frequency categories. In multivariable analyses, the hazard ratio for PCa incidence for 21 compared to 4–7 ejaculations per month was 0.81 (95% confidence interval[CI] 0.72–0.92; p < 0.0001 for trend) for frequency at age 20–29 yr and 0.78 (95% CI 0.69–0.89; p < 0.0001 for trend) for frequency at age 40–49 yr. Associations were driven by low-risk disease, were similar when restricted to a PSA-screened cohort, and were unlikely to be explained by competing causes of death.

Conclusions: These findings provide additional evidence of a beneficial role of more frequent ejaculation throughout adult life in the etiology of PCa, particularly for low-risk disease.

Patient summary: We evaluated whether ejaculation frequency throughout adulthood is related to prostate cancer risk in a large US-based study. We found that men reporting higher compared to lower ejaculatory frequency in adulthood were less likely to be subsequently diagnosed with prostate cancer.