Testosterone levels can vary depending on the time of day, the test used, the age of men sampled and their health, according to Carolyn Allan, a medical adviser to Andrology Australia, a government-funded research and education center in Melbourne.
A normal range for healthy, young adult men is 8 to 27 nanomolars per liter. Levels typically fall by 1 to 2 percent a year from about age 30, Allan says.
There’s some controversy about whether a drop in testosterone is due simply to age or medical conditions that occur more frequently in older age, said Ronald Swerdloff, professor of medicine and chief of endocrinology at Harbor-UCLA Medical Center in Los Angeles.
Testosterone should be kept above 8 nanomolars to avoid erectile dysfunction and above 10 to prevent bone loss, Allan said. Levels above 15 will help protect against increased accumulation of body fat and a flagging libido.
The findings of a study in Germany presented at a medical meeting in June showed the hormone helped obese men with low testosterone levels lose weight and keep it off. The study followed 214 men for at least two years and 115 for at least five. Their cholesterol, blood-sugar and blood pressure also improved with the treatment.
Australia’s National Health and Medical Research Council is committing A$4.5 million ($4.6 million) to a study seeking to establish whether testosterone, combined with diet, is safe and effective in mitigating diabetes risk.
Current recommendations to prevent or delay type 2 diabetes focus on reducing body fat and exercising, which fails to stop as much as 30 percent of those at risk of the obesity-linked condition developing it within five years. The International Diabetes Federation says the disease costs $471 billion to treat worldwide.
The scientists aim to recruit 1,500 pre-diabetic men ages 50 to 74 years with relatively low testosterone and waist circumference of 95 centimeters (37 inches) or more. Participants will receive free access to a weight-loss program provided by Weight Watchers International and treatment with either testosterone or a placebo.