Cancer Risk 'Increases With Increasing Number of Sex Partners'

Liam Davenport

February 14, 2020

The more sexual partners an individual has had during their lifetime the greater their risk of a cancer diagnosis, potentially due to a higher likelihood of contracting sexually transmitted infections (STIs), UK researchers have discovered.

They analysed data on more than 5700 men and women who took part in a longitudinal study on ageing in which they were asked about their number of sexual partners during their lifetime.

The results indicated that, among men, having 10 or more lifetime sexual partners increased the risk of a cancer diagnosis by 69% compared with having one or no sexual partners. In women, the risk was increased by 91%.

Sex Questions

The research, which was published by BMJ Sexual and Reproductive Health on 13th February, also revealed than women who reported five or more sexual partners were 64% more likely to have a life-limiting chronic condition.

The authors suggest that, "enquiring about the number of sexual partners a patient has had may be a simple and cost-effective complement to existing cancer screening programmes in identifying those at risk of certain cancers".

However, they add that, "further work is required first in order to replicate our findings and establish whether a causal relationship exists".

They also underline that, due to the nature of the study, "it is possible that the association between the number of sexual partners and cancer was a chance finding".

Nevertheless, the team suggests that an individual’s number of sexual partners "captures a combination of likelihood of exposure to STIs and lifestyle profile".

Gender Differences

Study co-author Dr Lee Smith, The Cambridge Centre for Sport and Exercise Sciences, Anglia Ruskin University, Cambridge, said that the potential link with STI history could explain the stronger relationship between the number of sexual partners and cancer risk in women than in men.

He told Medscape News UK that "we know that there’s a strong link between human papillomavirus [HPV] and cervical cancer", whereas the link between HPV and, for example, penile cancer is not as strong.

Dr Smith also underlined that, although it could be that people with "a greater number of sexual partners just generally lead more unhealthy lifestyles or engage in other kinds of risky behaviours that could be associated with cancers in later life," they did control for factors such as smoking and alcohol consumption in their analysis.

He emphasised that results suggest that people "of course should engage in safe and protected sex" but "if they have had unprotected sex in the past or a risky sexual encounter, they should make their healthcare provider aware".

Specific Cancers

The researchers note that STIs are associated with an increased risk of cancers, with HPV linked to not only the vast majority of cases of cervical cancer but also cancers of the mouth, penis, and anus.

Moreover, gonorrhoea infection is associated with prostate cancer risk in black men, and both hepatitis B and C are linked to an increased risk of developing liver cancer.

The researchers therefore suggest it is "plausible" that the higher the number of lifetime sexual partners, the greater the risk of contracting STIs and, subsequently, later health complications.

They add that, "given that STIs often go undiagnosed", an individual’s lifetime number of sexual partners could be a proxy for sexual risk behaviour.

Survey Data

To investigate further, the team examined cross-sectional data from the English Longitudinal Study of Ageing, which included men and women aged 50 years or more who responded to the Health Survey for England.

The analysis focused on the sixth wave of the study, conducted in 2012/13, as it was the first in which participants were asked about their number of sexual partners, via the Sexual Relationships and Activities Questionnaire (SRA-Q).

They included 2537 men and 3185 women in the sample. They had a mean age of 64.3 years and 65.3 years, respectively, and 93.7% of men and 96.0% of women were white.

The majority of men (73.6%) and women (60.6%) were married or cohabiting.

The vast majority of men (85.5%) and women (86.9%) were non-smokers, and 84.0% and 69.9% drank alcohol regularly or frequently. Moderate or vigorous activity was undertaken at least once a week by 80.2% of men and 74.8% of women.

As few participants reported having zero or 20 or more partners on the SRA-Q, the team combined those with the proximal categories, finding that, among men, 28.5% reported having 0–1 lifetime sexual partners, 29% 2–4 partners, 20.2% 5–9 partners, and 22.2% ≥10 partners.

Among women, 40.8% reported having 0–1 lifetime sexual partners, 35.5% 2– 4 partners, 15.8% 5–9 partners, and 7.8% ≥10 partners.

A higher number of lifetime sexual partners was associated in both men and women with younger age, being unmarried, and being in the highest or lowest quintile of wealth.

Moreover, respondents with a higher number of sexual partners were more likely to report smoking, frequent alcohol use, and engaging in physical activity on a weekly basis.

Study Findings

Using logistic regression analysis taking into account these factors, as well as ethnicity and depressive symptoms, the team found that there was an association between the number of lifetime sexual partners and a cancer diagnosis.

Compared with having had 0–1 sexual partners, 10 or more sexual partners was associated with an odds ratio of a cancer diagnosis of 1.69 in men (p=0.047) and 1.91 in women (p=0.038).

Although there were differences in rates of cancer diagnoses between those reporting 0–1 sexual partners and those reporting 2–4 and 5­­–9 partners, they did not reach statistical significance.

There was, in women, a significant association between the number of sexual partners and the risk of a life-limiting longstanding illness.

Compared with women who had had 0–1 sexual partners, those reporting 5–9 lifetime sexual partners had an odds ratio of a longstanding illness of 1.64 (p=0.003). In women reporting at least 10 partners, the odds ratio was the same, at 1.64 (p=0.007).

There was no association between the number of lifetime sexual partners and self-rated health, coronary heart disease risk, or stroke risk in either men or women.

No funding or conflicts of interest declared. 

BMJ Sex Reprod Health 2020;0:1–8. doi:10.1136/bmjsrh-2019-200352

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