WASHINGTON: Obese men often experience a sharp decline in testosterone levels while obese girls show much higher levels of the sex hormone than girls of normal weight, according to scientific research released on Monday.

Two separate studies published in the Journal of Clinical Endocrinology and Metabolism could indicate increased health risks for both grown men and teen-age girls who are obese.

Testosterone is the primary sex hormone for men, though it is found in women as well. It helps maintain muscle mass and bone density and keeps sex drive and physical energy at healthy levels. Testosterone levels naturally decline as men age. But those who put on weight - as little as 13.6 kg for a 6-foot man - lost as much testosterone as if they had aged 10 years.

Obese girls going through puberty had the opposite problem, a separate study found. Researchers at the University of Virginia and several other universities found that obese girls had two to nine times the levels of testosterone as girls of normal weight, which could impair reproductive health.