It's safe to say your teenage years probably aren't the time when you're most worried about your health, but according to the authors of a new report, what happens during adolescence can play a huge role in determining your health for the rest of your life.The report , which was published in the Lancet and is the result of a commission to look at health challenges facing young people worldwide, found that today's teens are growing up in a world where preventable and treatable health issues, such as HIV/AIDS and unplanned pregnancy, abound.Among the most shocking findings of the report: For women between the ages of 10 and 24, unsafe sex is the fastest-growing risk factor for illness and death worldwide.Related: Have Better Sex With One Of These 5 Condoms To determine the major causes of death among young people, the report's researchers observed changes in this group's health over 23 years. At first, STIs didn't even rank as a risk factor for death, but nevertheless, they reached number one by the end of the research period.The importance of safe sex has been stressed with increasing urgency over the years. But, unfortunately, other studies have found that STI rates are on the rise.Related: How To Find the Best Birth Control For You