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Numerous factors -- including body mass index (BMI), lifestyle, relationship status, and a number of disease states -- were tied with declining testosterone levels in men over 70, researchers found.

In a meta-analysis including about 25,000 men, testosterone levels were fairly stable from ages 17 to 70, but then started to significantly drop after that (-44.7 ng/dL change per SD increase, 95% CI -59.1 to -30.6), Bu B. Yeap, MBBS, PhD, of University of Western Australia in Perth, and colleagues reported in . One SD increase was about 15 years.

After age 70, Yeap's group found several clinical and lifestyle factors that were related to this testosterone drop.

"One of the findings which we were struck by, was that after allowing for other factors, testosterone levels are in fact stable until the age of about 70 years," Yeap explained to MedPage Today. "After that age, testosterone levels declined with age, despite increasing levels of the pituitary hormone that drives testosterone production by the testis."

"This indicates that production of testosterone by the testis in men is impaired after the age of 70 years," he said.

BMI was inversely associated with testosterone levels, with every SD increase in BMI linked to a -69.7 ng/dL (95% CI -77.8 to -61.4) drop in testosterone. Only men with a BMI over 32 had higher estradiol concentrations.

Similarly, men who engaged in vigorous physical activity for 75 minutes or less per week saw significantly lower testosterone levels (-14.7 ng/dL, 95% CI -25.9 to -3.7), as did former smokers (-9.8 ng/dL, 95% CI -15.9 to -3.5).

"Men should be encouraged to engage in healthy lifestyle behaviors, as this should help maintain their body's own testosterone production," advised Yeap.

Interestingly, married men -- or otherwise in a relationship -- also had significantly lower testosterone levels independent of age (-16.4 ng/dL, 95% CI -25.6 to -7.5).

"A possible explanation could be that married men with families might be more stressed, and therefore have lower testosterone levels," Yeap suggested, "but our study wasn't designed to look further into this result."

In addition, researchers found having a history of several health factors was associated with significantly lower testosterone levels after surpassing age 70, including:

• Hypertension -15.3 ng/dL (95% CI -23.6 to -6.9)
• Cardiovascular disease: -10.1 ng/dL (95% CI -15.9 to -4.3)
• Cancer: -40.1 ng/dL (95% CI -51.6 to -28.5)
• Diabetes: -41.2 ng/dL (95% CI -47.6 to -35.2)

Beyond testosterone, Yeap's group found that sex hormone-binding globulin was likewise associated with age and inversely associated with BMI. Luteinizing hormone was also directly linked with age in men over 70.

"The main message is that a range of sociodemographic, lifestyle, and medical factors influence testosterone levels in men," said Yeap. "These need to be considered when clinicians interpret testosterone results from individual men, as testosterone levels might be lower than expected in the presence of these conditions, rather than being always due to a problem with the testes."

For the review, the researchers pulled individual participant data from nine studies, which included 21,074 men, plus aggregate data from another two studies, which included another 4,075 men. Studies were conducted across Australia, Europe, and North America. Total testosterone, dihydrotestosterone, and estradiol were measured using mass spectrometry. Sex hormone-binding globulin and luteinizing hormone were measured using immunoassay.

"Additional research is needed to determine mechanisms underlying the association of marriage with lower testosterone concentrations in middle-aged men and the implications of impaired Leydig cell function for the health of older men," the researchers concluded.

Correction: The paragraph about lower testosterone levels in married men was updated to reflect that the finding was independent of age.

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