For guys without hypogonadism, a wait-and-see approach may make the most sense. "We just don't have the data to prove that raising testosterone in men who already have normal levels confers any real benefit," says Dr. Robert Mordkin , a urologist in Arlington, Virginia. Furthermore, Mordkin adds, "Natural waxes and wanes of testosterone as we age may have some not yet entirely understood protective effects." In addition to making us better fathers, as the Northwestern study infers, declining testosterone "may lower our vulnerability to prostate cancer at a time in our lives when we're at the greatest risk for it." That said, if you have classic symptoms of hypogonadism – low libido, fatigue, erectile dysfunction – "it's probably reasonable to check your testosterone. And for those guys whose blood levels come under definitions of low testosterone, it's probably reasonable to try the therapy for a while. But that's very different from saying testosterone is the fountain of youth."