Endocrine Abstracts

Background: Presently it is unknown how much of testosterone decline associated with aging is actually due to ageing per se, and how much is related to weight gain, decreased activity, and other age-related factors. Understanding the modifiable factors associated with low testosterone, such as obesity or cardiorespiratory fitness (fitness) is critical.

Methods: The observational, cross-sectional study included 1653 men, ≥50 and <80 years of age, seen between January 2012 and December 2012 for a preventive medical examination and underwent BMI, total testosterone, and objective fitness measurements as defined by the total duration of time on a maximum Balke treadmill test. Treadmill time was then used to estimate metabolic equivalents (METs). All participants underwent morning (0700–0900 h) total testosterone measurement using the standard chemiluminescence method. Testosterone thresholds were categorized into low (<250 ng/dl), low normal (250–<400 ng/dl), and normal (≥400 ng/dl). We used traditional sample statistics to summarise characteristics of the sample within decades of age and ordered categories of BMI.

Results: While levels of mean testosterone levels in all age groups were in the normal range were statistically different between groups, (50–59 years, testosterone mean=479.0 ng/dl (S.D.=175.4); 60–69 years, testosterone mean=457.2 ng/dl (S.D.=204.1); and 70–79 years, testosterone mean=464.6 ng/dl (S.D.=176.7); trend P value=0.05), although, the trend was statistically different, mean testosterone levels in all groups were in the normal range. The prevalence of low testosterone did not significantly differ between 50–59, 60–69, and 70–79 age groups (<250 ng/dl=7.6–9.3% to 8.7%; trend test P=0.17) but did change with increasing BMI, (<250 ng/dl=3.4–6.8% to 17.8%; trend test P<0.001). Finally, fitness was positively correlated with total testosterone levels (P<0.001) and this correlation persisted after adjustment for age and BMI.

Conclusion: In this group of generally healthy men, there was no decrease in the mean total testosterone level with increasing age, yet we found statistically and clinically negative correlation between testosterone and BMI and positive correlation between testosterone and fitness.