Tuesday January 27 2009
The Independent has reported that “masturbation can be good for the over-50s” claiming it may remove toxins and reduce the risk of prostate cancer. The Sun reported that “solo sex” during one’s younger life might increase the risk of prostate cancer. These claims are based on research exploring prostate cancer and sex drive, which some suggest are both linked to high levels of male hormones.
The research surveyed 431 men who were diagnosed with prostate cancer before the age of 60 and 409 healthy men, asking about sexual habits at various stages of their lives. It was found that frequent masturbation during one’s 20s and 30s was associated with an increased risk of prostate cancer, while men who masturbated more frequently in their 50s had a lower risk.
This study has a number of limitations, in particular, asking men to accurately recall their sexual habits several decades ago. Also, because sex is a highly personal matter some men may have felt uncomfortable revealing such personal details about their lives, or may have defined sexual activities differently. For these reasons men may have easily over- or underestimated their sexual activity.
Sexual functioning is a normal part of healthy adult life and men should not be overly concerned by this study, as more research is needed in this area.
Where did the story come from?
This research was conducted by Prof Muir and colleagues from the University of Nottingham Medical School, Chulabhorn Cancer Hospital in Bangkok, the University of Cambridge, Royal Devon and Exeter NHS Trust and Institute of Cancer, and the Royal Marsden NHS Foundation Trust.
The study was funded by the Prostate Cancer Research Foundation and Cancer Research UK.
It was published in the British Journal of Urology International, a peer-reviewed medical journal.
What kind of scientific study was this?
This was a case-control study looking at the association between prostate cancer risk and sexual activity in men. It focussed on men diagnosed with prostate cancer relatively young, below the age of 60.
Recent research has reportedly associated sexual activity with risk factors for prostate cancer. It's been suggested that men with greater sex drive have higher male hormone levels. Since prostate cancer is known to be hormonally dependent, in theory having a higher sex drive as a result of male hormone levels could also be linked to an increased risk of prostate cancer.
It is thought that around 75% of prostate cancer diagnoses are in men over the age of 65, with only a quarter being diagnosed before this age. This study aimed to investigate this younger minority of cases.
The researchers used the Prostate Cancer Research Foundation Study to identify 431 men diagnosed with symptomatic prostate cancer before the age of 60. This was the case group. The cases were matched to 409 control subjects who were recruited through their GP.
All participants completed a postal questionnaire on lifestyle and sexual activity throughout adult life. This included asking about the number of sexual partners, age of first sexual experience, any sexually transmitted infections, and frequency of sexual intercourse or masturbation in their 20s, 30s, 40s and 50s.
Frequency responses were given in ranges and an overall frequency value for that decade calculated. Frequency of activities was categorised as never, less than once per month, one to three times per month, once a week, two to three times per week, four to six times per week, and daily.
The researchers then looked at whether there was a link between frequency of sexual activity and risk of prostate cancer. In their analyses they took into account factors that might affect results, which included age and ethnicity, as well as other factors found to differ between cases and controls.
What were the results of the study?
Postal questionnaires were responded to by 73% of the case group and 74% of the control group.
Overall, 59% of men reported a sexual activity (sexual intercourse and masturbation) frequency of 12 or more times per month whilst in their 20s, decreasing to 48% in their 30s with this frequency, 28% in their 40s, and 13% in their 50s.
Various differences were found between cases and controls; those in the case group were more likely to have had a full/obese shape across decades, to have had a sexually transmitted infection, to have a genital sore/ulcer and to have had more female partners. The researchers adjusted for these factors in their later analysis.
In the initial analysis the researchers only adjusted for differences in age and ethnicity: this showed no significant link found between prostate cancer and frequency of overall sexual activity (sexual intercourse and masturbation) in any decade, or lifetime sexual activity.
Masturbation more than once a week in the 20s, 30s and 40s age categories was associated with increased risk of prostate cancer compared to never masturbating. There were no significant links found between prostate cancer and masturbation in the 50s.
Researchers performed further analysis also taking into account the other differences between cases and controls. After these adjustments the significantly increased risk of prostate cancer remained for those who masturbated more than once weekly whilst in their 20s and 30s. No link was found in the 40s age category, whilst masturbation more than once weekly in the 50s category decreased risk.
There was no link between prostate cancer risk and frequency of sexual intercourse in any decade. More frequent overall sexual activity in the 50s significantly decreased prostate cancer risk, but there was no link with overall sexual activity in any other decade.
What interpretations did the researchers draw from these results?
The researchers conclude that there seemed to be a risk from more frequent masturbation in the 20s and 30s, but a protective effect in the 50s.
They say that this could imply different mechanisms at different ages by which sexual activity is involved in the development of prostate cancer. They also suggest that part of the effect seen in the 50s might be a result of “reverse causality” where prostate cancer affected the men’s sexual activity, rather than the other way around.
What does the NHS Knowledge Service make of this study?
The study has found a link between increased frequency of masturbation in the 20s and 30s decades and increased risk of prostate cancer, but a seemingly protective effect with the same frequency in the 50s. The reasons for this are unclear and this will need further research.
However, there are numerous potential limitations which must be considered when interpreting this study. The principle limitation is the reliability of the estimates of sexual activity, though it should be noted that the researchers attempted to minimize this bias through use of a long and extensive questionnaire. There are problems with the use of estimation, including:
- Asking men to recall their sexual activity and frequency across decades of life from their 20s, 30s, 40s and 50s. This is going to involve a lot of estimation inaccuracy.
- Sexual activity is a highly personal matter. Some men may feel uncomfortable revealing such personal detail and may therefore have either over- or underestimated their activity, depending on their feeling to answering.
- What constitutes a certain sexual activity to one person may not mean the same thing to another person.
There are also other limitations to take into account when interpreting this study and its coverage in the media:
- As with all studies of this type, an association between two factors does not necessarily mean that one causes the other. Other factors (confounders) that have not been adjusted for may affect the links found to masturbation.
- The study involved a lot of statistical comparisons. As more tests and combinations are made, the more likely it is that a result that occurs by chance will appear to be significant.
- There was a link found between cancer risk and frequency of masturbation, but no link was found to frequency of sexual intercourse. When both masturbation and intercourse were combined to give the variable of overall sexual activity, decreased risk was found with increased sexual activity in the 50’s, but no link was found for any other age group.
- These were a specific group of people with prostate cancer who were all diagnosed with cancer prior to the age of 60. The men in this study are not typical of the vast majority of people with prostate cancer, who are generally diagnosed over the age of 65. Therefore there may be particular unknown characteristics of these people that makes them more predisposed to prostate cancer at a younger age. The results may also not be representative of what would be seen in men who develop prostate cancer later in life.
- The study involved predominantly white men. Prostate cancer has been linked to ethnicity, with men of African-American origin believed to be at increased risk. Although the researchers did make careful attempts to adjust for ethnicity in their analysis, a wider ethnic representation may have given different results.
Men should not be overly concerned by this research. Sexual functioning is a normal part of healthy adult life. The causes of prostate cancer are not known for certain. Increasing age is the most established risk factor and more research is needed.