Early initiation of sexual intercourse is associated with an increased likelihood of STD infection among teenagers and young adults overall, but the magnitude and strength of the association vary by current age, according to findings from the National Longitudinal Study of Adolescent Health (Add Health).1 In analyses of data on respondents who provided urine samples for STD testing in Wave 3 of the survey, teenagers who had first had intercourse at an early age were more likely than their peers who had waited to test positive. However, the older the respondent, the less pronounced the difference, and for 24-year-olds, the association was no longer statistically significant. The relationship between age at first sex and STD infection did not vary by other characteristics studied.
To examine long-term associations between age at first intercourse and STD risk, analysts studied data from 9,844 sexually experienced Wave 3 Add Health respondents who provided a urine specimen to be tested for chlamydia, gonorrhea and trichomoniasis. They used multiple logistic regression and included interaction terms to assess whether associations varied among young people with different demographic characteristics.
The sample was evenly divided between males and females; 80% of the young people were white, and 90% were non-Hispanic. Nearly nine in 10 said that at least one parent had a high school or higher education. At the time of Wave 3 (2001-2002), respondents were 18-26 years old; their mean age was about 22 years. On average, they had been about 16 years old when they first had intercourse; one in three had been younger than 16.
Seven percent of respondents tested positive for at least one STD. This group was disproportionately female (58%) and black (51%), and reported a lower level of parental education than did the overall sample. Forty-six percent of those who had an STD had been younger than 16 at first intercourse. The proportion with an STD declined from about 10% of those who had first had sex at age 12 to about 6% among those who had delayed first intercourse until age 20.
Both current age and age at first intercourse were negatively associated with young people's likelihood of having an STD. Results of the multivariate analysis showed, however, that the older the respondent, the smaller the increase in risk related to age at first intercourse. For example, compared with their peers who had first had sex at age 17, 18-year-olds who had initiated intercourse at age 13 had more than twice the odds of being infected (odds ratio, 2.3), but 24-year-olds who had begun intercourse at age 13 had only a small increase in odds that was not statistically significant (1.1).
Other factors associated with an elevated likelihood of testing positive for an STD were being female (odds ratio, 1.4), being Hispanic (1.8) and being nonwhite (6.0 for blacks and 1.7 for others). Respondents who reported that at least one parent had completed high school or received a postsecondary education had reduced odds of being infected (0.6-0.8). The association between age at first intercourse and the likelihood of having a positive STD test did not differ by these characteristics.
The analysts conclude that "programs that effectively prolong virginity among adolescents make sense as part of a comprehensive strategy for reducing [STDs] among adolescents." By the same token, they emphasize that such programs "will have limited returns in terms of reproductive health among young adults." They suggest that early intercourse, in and of itself, may not be responsible for heightened STD risk among young people, and that different mechanisms may be effective for reducing STD rates in late adolescence and young adulthood.
1. Kaestle CE et al., Young age at first sexual intercourse and sexually transmitted infections in adolescents and young adults, American Journal of Epidemiology, 2005, 161(8):774-780.