Testosterone

Testosterone is the main male sex hormone. Levels drift down with age, but gaining weight or losing health can pull them down about as much as age does. Evidence: decent

Low testosterone is a diagnosis, not a feeling. The guideline asks for two things together: symptoms, and low levels in blood taken in the morning, on more than one occasion. Evidence: solid For the kind that turns up later in life, one study could only pin it down as sexual symptoms and low blood levels, both at once. Evidence: decent Tiredness on its own is a weak sign of it, whatever the ads say. Evidence: decent

"Low T" marketing and booster supplements are oversold, and so is the idea that testosterone is what makes men aggressive: there is a link, but it's small. Evidence: decent If yours is confirmed and treatment comes up, know the trade-off. In a trial of men with confirmed low levels who had heart disease or a high risk of it, testosterone gel did no worse than a dummy gel on serious heart events. It did bring more irregular heartbeat, sudden kidney damage and blood clots in the lungs. Evidence: decent Treatment also lowers sperm production, so if you still want children, tell the doctor before you start. Evidence: solid Some booster supplements contain vitamin and mineral doses above safe limits. Evidence: decent