Hear the word testosterone, and I know immediately what you're thinking. You know it's what puts the moan in hormone. You think of muscle, of sex drive, of bravado. It's the vitality hormone that gives men the strength to win a fistfight (and the guts or stupidity to get into one in the first place). And it's the hormone that partly controls how much sex men want—and whether or not they're going to experience erectile dysfunction.
Most men produce 4 to 7 milligrams of testosterone a day, with the highest blood level in the morning and the lowest level in the evening (which helps explain why the first thing some men want in the morning is neither coffee nor a shower).
Science has yet to explain why the levels rise and fall at these times, but it may be related to action of the brain's pituitary gland. For practical purposes, those time frames do give some insight into why the so-called nooner can be an effective way to match a couple's sexual urges.
Find out more about this book:You: Staying Young: The Owner's Manual for Extending Your Warranty