Background: To examine sexual behaviors among people aged 14–59 years in the United States.
Methods: Using data from the National Health and Nutrition Examination Surveys from 1999-2010, we analyzed: 1)trends in age at sexual initiation, number of sex partners, and same-sex partner report by 10-year birth cohorts among adults >30 years; and 2)patterns of sexual practices among participants ≤30 years. Estimates were adjusted for demographic factors prior to significance testing. Sex was defined as vaginal, oral, or anal.
Results: Adults born in more recent birth cohorts were younger at sexual debut than those born in previous periods (Ptrend<0.001); this trend was more pronounced among women. Among women born in 1940-49 and 1970-79, 6.6% and 15.1% reported sex before age 15. Among men born in 1940–49 and 1970-79, 14.9% and 18.6% reported sex before age 15. The percentage of adults reporting >10 lifetime partners increased in later birth cohorts, from 16.9% of women born in 1940–49 to 32.3% of in 1970–79; and from 41.2% of men born in 1940-49 to 48.7% in 1970-79. The percentage of women reporting ever having same-sex partners increased with successive cohorts, from 5.2% in 1940-49 to 9.4% in 1970-79 (Ptrend<0.001); this trend was not seen in men. Among participants aged 14, 16, and 20 years, 13.7%, 40.9%, and 84.1% reported ever having sex; with no difference between genders. There was no change by 2-year survey intervals from 1999-2010. Among sexually active 14 year-olds, 46.0% of males and 22.3% of females had ≥3 lifetime partners.
Conclusions: Among participants aged >30 years, age at sexual initiation decreased while number of sex partners increased in more recent birth cohorts, especially among females. Over the past decade, the percentage of participants aged ≤30 years reporting sexual activity by ages 14, 16, and 20 remained stable.