It's established science that as we get older, testosterone levels often drop, Hegseth says in a video on X.
Testing for the male sex hormone should be done in conjunction with annual health checks. If levels are low, soldiers should be advised about treatment, but it should be voluntary.
Women's testosterone levels also often decline over the years, but it is not clear from Hegseth's video whether they are covered by the new regulations.
U.S. special forces have often come under scrutiny in recent years for taking extra testosterone and similar substances in the hope of becoming better soldiers, writes the AP news agency.
