Cycling for Health UK Fact Sheet

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1 Cycling for Health UK Study: An observational study of erectile dysfunction, infertility and prostate cancer in regular male cyclists Fact Sheet Written by Dr Milo A Hollingworth, University College London What do we already understand about cycling and its relationship with erectile dysfunction, infertility and prostate cancer? Cycling has been implicated in health problems affecting the male urogenital organs including inflammation of the prostate (prostatitis), blood in the urine (haematuria), erectile dysfunction (impotence) and infertility. In addition to this, cycling is associated with increases in levels of prostate specific antigen (PSA) levels. The prostate releases PSA and it can be raised due to cancer, inflammation and trauma affecting the prostate. However, cycling has never previously been linked to prostate cancer. It has been hypothesised in the past that cycling can cause erectile dysfunction and infertility. Erectile dysfunction has been studied amongst cyclists undertaking mass participation cycling events, and also using measurements of blood flow to the penis during cycling. These studies suggested that cycling increased the risk of erectile dysfunction. Regarding infertility and cycling, research identified sperm abnormalities suggestive of infertility amongst cyclists. Despite this research, little evidence exists regarding erectile dysfunction and infertility in the context of habitual real- life cycling. In studies on the population, cause and effect relationships often demonstrate dose response relationships. Using smoking as an example, one would expect risk of lung cancer to increase with increasing levels of smoking. Therefore, we hypothesized that if erectile dysfunction and infertility were caused by cycling we would expect to see increasing risk of erectile dysfunction and infertility with increasing cycling levels. In addition to this, risk of prostate cancer was of interest considering the effects cycling has on PSA levels.

2 How did we conduct the study? We conducted an online survey of 5282 male cyclists looking at personal details (including age and gender) cycling habits (including weekly distance and time) and common health problems (including high blood pressure, heart disease, diabetes and cancer). Diagnosis was defined as being told by a doctor that they had the disease. These details were all self- reported. Statistical analysis was used to remove the impact of factors such as age, alcohol intake and smoking might have had on the data. Males over 50 years were specifically analysed for diagnosis of prostate cancer, as prostate cancer is rare under the age of 50 years. This sub- group comprised of 2,027 males with ages ranging between years. What did we find? Erectile dysfunction Increasing cycling time was not associated with increasing reports of erectile dysfunction. Infertility Increasing cycling time was not associated with increasing reports of infertility. Prostate cancer 36 men reported being diagnosed with prostate cancer, 17 of which reported cycling levels greater than 8.5 hours per week: Data from 2,027 male cyclists regarding prostate cancer and weekly cycling time Cycling hours per week Cases of prostate cancer reported Less than 3.75 hours per week 3 Between 3.76 and 5.75 hours per week 7 Between 5.76 and 8.5 hours per week 9 More than 8.5 hours hours per week 17 Total 36/2,027 cyclists

3 Statistical testing demonstrated that there was an upgoing trend between prostate cancer diagnosis and weekly cycling time. This reached statistical significance, which means our findings were unlikely to be due to chance. This data was analysed using techniques to remove the influence of factors such as age, smoking and alcohol intake. According to our data, men cycling over 8.5 hours per week were 6 times more likely to have received a diagnosis than those cycling less than 3.75 hours per week. What did we conclude? Erectile dysfunction Our data challenges the simple cause- and effect relationship between cycling and erectile dysfunction previously suggested. Although, we cannot deny that erectile dysfunction is a problem amongst cyclists, it is not simply that increasing cycling increases risk of erectile dysfunction. For example, erectile dysfunction is also affected by poor cardiovascular health, which may be prevented by cycling. Our data may also be affected by use of modern bicycle design Infertility The suggestions of cycling causing infertility, based on measurements of sperm characteristics, were not born out in our population data. Prostate cancer We found an up- going relationship between prostate cancer diagnoses and cycling time, suggesting that cycling hours per week were positively associated prostate cancer diagnosis. This has never been found before and it is subject to many interpretations, which include but are not limited to the following: Prostate cancer in some way is caused by cycling, potentially due to trauma or inflammation of the prostate Cycling increases levels of PSA which in turn lead to increased rates of investigation for prostate cancer Cyclists are more health- literate and are aware of the dangers of prostate cancer and consult their doctors more readily

4 Cyclists are more likely to suffer urogenital abnormalities such as blood in the urine or pain around the prostate making them more likely to be tested for prostate cancer Cycling time and prostate cancer are both associated with an unknown factor that was not accounted for by our study Most importantly, our study is the first piece of research to explore the link between prostate cancer and cycling. Many other different studies using different methods are required to investigate this further. What are the strengths of the study? Our study uses data from real- life cyclists Our study is the largest of its kind Our study recorded detailed information regarding cycling activity What are the weaknesses of the study? Our study is observational and cannot determine cause and effect relationships Our study is dependent on self- report which may be subject to some inaccuracy Our study looks back in time at those who have already been diagnosed, this kind of design can often over- emphasize certain relationships Our study cannot differentiate between high grade and low grade prostate cancer Was study funded or influenced by any third parties? This research did not receive any specific funding and the design of the study was not influenced by any third parties What s the take home message? Cyclists should not necessarily worry that cycling well definitely causes erectile dysfunction. If men experience symptoms of erectile dysfunction, they should consult their doctor, altering their cycling saddle or cycling habits may help to improve symptoms.

5 We have no evidence to suggest that cycling will negatively affect your fertility. We cannot say on the basis of our results that prostate cancer is caused by cycling. We would not recommend that people reduce their cycling volume. Cycling has many physical and mental health benefits that at present outweigh any risks it may cause. This research should prompt further investigation using different study designs. Where can you find out more information? Leibovitch I, Mor Y. The vicious cycling: bicycling related urogenital disorders. Eur Urol 2005;47(3): Gebreegziabher Y, Marcos E, McKinon W, Rogers G. Sperm characteristics of endurance trained cyclists. Int J Sports Med 2004;25: Mejak S, Bayliss J, Hanks S. Long distance bicycle riding causes prostate- specific antigen to increase in men aged 50 years and over. PLoS One 2013;8(2):e56030.