NEW YORK: Older men with low levels of the hormone testosterone may die sooner than other men their age with normal testosterone levels, a study suggests.

Researchers found that among 794 generally healthy older men, those with the lowest testosterone levels were 40% more likely to die within the 1985-2004-study period.

The findings do not mean, however, that older men should start taking testosterone supplements to achieve a longer life, the study authors are quick to point out.

The study shows only an association between low testosterone and earlier death - not a cause-and-effect relationship, lead author Dr Gail A Laughlin said. What's more, there was no evidence that having above-average testosterone levels gave men any longevity advantage. "We cannot recommend that any man take testosterone based on these results," Laughlin stressed.

She and her colleagues at the University of California, San Diego, report their findings in the Journal of Clinical Endocrinology & Metabolism .

In theory, low testosterone could affect older men's longevity through metabolic effects. Some past studies have found that low testosterone can precede the development of abdominal obesity and the metabolic syndrome - a collection of risk factors for diabetes and heart disease that includes obesity, high blood pressure and unhealthy cholesterol levels.

In their study, Laughlin and her colleagues found that low testosterone was associated with abdominal obesity and aspects of the metabolic syndrome, but when these factors were excluded, low testosterone remained independently linked to earlier death.

The study included 794 men between 50 and 91 year old (average age 73.6 years) who were followed for an average of 11.6 years. Overall, the one quarter with the lowest testosterone levels at study entry were 40% more likely to die over the course of the study than men with higher levels of the hormone.

There is some disagreement among experts on how to define overt testosterone deficiency, with some saying it should be diagnosed when levels fall below 300 nanograms per deciliter (ng/dL) and others advocating lower cutoffs. There was no evidence in this study that raising older men's testosterone above 300 ng/dL might boost survival.