More than one in four young women first have sex below the age of 16 - a greater proportion than previous generations, figures suggest.
Data from the Health Survey for England show 27% of women aged 16 to 24 first had sex under the age of consent, compared with 22% of men of the same age.
The 2010 report suggests sexual behaviour has changed over the generations, with the proportion of women who first had sex below the age of 16 increasing over time.
Just 15% of men and 4% of women aged 55 to 69 said they first had sex under the age of 16, alongside 18% of men and 10% of women aged 45 to 54. Among those aged 35 to 44, 21% of men and 14% of women first had sex under 16.
Published by the NHS Information Centre, the report found that one in 10 young people aged 16 to 24 have had 10 or more sexual partners.
But 26% of women and 32% of men aged 16 to 24 say they have never had sex.
Young people are more likely than those who are older to have been tested for the sexually-transmitted infection chlamydia (27% of men and 44% of women aged 16 to 24 compared with 6% of men and 12% of women aged 45 to 54).
Across all age groups, men have typically had 9.3 female sexual partners in their lifetime, while women have slept with an average of 4.7 men.
Almost a quarter of all women (24%) have only ever had one sexual partner, compared to 17% of men. Some 13% of women have had 10 or more partners of the opposite sex, compared with 27% of men.
The report also found that obesity among adults is at the highest level since 1993. Some 26% of men and women were obese in 2010 and, overall, 68% of men and 58% of women were overweight or obese. The prevalence of obesity has increased from 13% in 1993 to 26% in 2010 among men, and from 16% to 26% among women.