Testosterone Tumbling in American Males

The testosterone-fueled American male may be losing his punch.

Over the past two decades, levels of the sex hormone in U.S. men have been falling steadily, a new study finds.

For example, average total testosterone levels in men aged 65 to 69 fell from 503 nanograms/decileter (ng/dL) in 1988 to 423 ng/dL in 2003.

The reasons for this trend are unclear, said researchers at the New England Research Institutes in Waterdown, Mass. They noted that neither aging nor certain other health factors, such as smoking or obesity, can fully explain the decline.