Testosterone supplementation for “low T” is not supported by evidence, review concludesBMJ 2016; 354 doi: https://doi.org/10.1136/bmj.i5166 (Published 22 September 2016) Cite this as: BMJ 2016;354:i5166
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Testosterone supplementation for men in the absence of pathological hypogonadism: more research needs to be done.
The comment by McCarthy  is consistent with a recent position statement from the Endocrine Society of Australia recommending testosterone replacement therapy for men with the clinical syndrome of androgen deficiency due to underlying hypothalamic, pituitary or testicular disease, but not for older men with comorbidities, obesity or diabetes who may exhibit “low testosterone” in the absence of pathological hypogonadism . However the conclusion by Huo et al  that further trials of testosterone are not necessary might be premature.
The US Testosterone Trials showed a moderate benefit of testosterone supplementation to improve sexual function in older men , proving causality for prior observational data . Additional outcome measures from that trial have yet to be reported. Epidemiological studies in middle-aged and older men implicate low testosterone with increased risk of metabolic syndrome  and diabetes . The ongoing Australia-wide study Testosterone for the Prevention of Diabetes Mellitus (T4DM, ACTRN12612000287831) in overweight men with impaired glucose tolerance will discover whether causality applies to diabetes risk. In older men low testosterone concentrations are independently associated with increased incidence of stroke  and with mortality . Testosterone’s bioactive metabolites dihydrotestosterone and estradiol may influence biological ageing favourably in men .
Thus the next challenge will be to design and conduct adequately powered randomised controlled trials to determine the effect of testosterone on cardiovascular and mortality risk. The systematic review by Huo et al  defines the limits of available evidence, illuminating by extension the scope of our current ignorance. Additional clinical studies, particularly randomised controlled trials, are vital to inform health care for the increasing demographic of men at risk of ill-health who wish to age well.
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Competing interests: I have received speaker honoraria and conference support from Bayer, Eli Lilly and Besins, research support from Bayer, Eli Lilly and Lawley Pharmaceuticals, and participated in Advisory Boards for Eli Lilly and Besins.