Background

There is a large body of literature investigating the relationship between sexual activities, including total number of sexual partners, and risk of developing sexually transmitted infections (STIs). To date, most of this research has focused on adolescents and young adults or the cost-effectiveness of preventative strategies.1 Studies have shown that a greater number of sexual partners is associated with greater risk of contracting STIs in adolescents.2

STIs can have long-term consequences for health, including greater risk of specific cancers. Rates of human papillomavirus (HPV) infection in sexually active young females have been consistently reported to range from 19% to 46%.3 Nearly all cases of cervical cancer can be attributable to HPV infection.4 Moreover, HPV has been found to be associated with cancers of the mouth, penis and anus,4 cancers that are most common in older adults.5 6 Other STIs, such as gonorrhoea infection, have been shown to increase the risk of prostate cancer in black men.7 The average age for men to be diagnosed with prostate cancer is between 55 and 69 years.8 Therefore, STIs may have a long lasting negative impact on adults later in life. Investigations into infection–cancer associations have shown that hepatitis B and hepatitis C are associated with a much higher risk of developing liver cancer,9 a common cancer among older adults with a peak rate between the ages of 85 to 89 years.10 People living with HIV are also more susceptible to several types of cancers.11 Besides cancer, STIs have also been found to be associated with diseases of the cardiovascular system.12

It is plausible that a greater number of lifetime sexual partners in older adults increases the risk of contracting an STI over the lifespan and subsequently increases the risk of developing health complications in later life. Given that STIs often go undiagnosed, number of sexual partners could provide a proxy measure of sexual risk behaviour that is more accurately reported (although likely subject to potential underreporting by people with a higher number of partners). Establishing the extent to which number of sexual partners is associated with health problems is important in gauging the potential utility of this measure as an indicator of risk.

Previous studies that have investigated the number of sexual partners and cancer risk have shown mixed findings. In a sample of black men, those reporting 25 or more sexual partners were found to be 2.80 (95% CI 1.29 to 6.09) times more likely to be diagnosed with cancer compared with men with five or fewer partners.13 Other research has found similar findings in more diverse samples in relation to anal cancer, prostate cancer and oral cancer.7 14 15 In contrast, a study using a Canadian population found reduced risk of prostate cancer among men with more than 20 sexual partners in their lifetime.16 Little research has been carried out examining the role of number of sexual partners as a behavioural risk factor for wider health outcomes in older adults.

To fill these knowledge gaps, the aim of the present study was to investigate the sex-specific associations between the number of lifetime sexual partners and several health outcomes in a large sample of older adults in England. We hypothesised that a greater number of previous sexual partners would be associated with increased risk of unfavourable health outcomes.