Injectable testosterone: Age effects conversion to Estrogen & DHT
Injectable testosterone: Age effects conversion to Estrogen & DHT by Anthony Roberts
A recently published study examined the effects of various doses of injectable testosterone in young (<35 years) and old (>52 years) men. Conversion to estrogen was higher in older men, while conversion to DHT was the same for both groups. Age-related differences in free E2 (estradiol) and free E2:Testosterone ratios were insignificant after adjustments were made for fat mass, and SHBG (which were higher in the older group).
This is interesting because it may suggest that older men who are on HRT should consider the additional use of an aromatase inhibitor, such as Aromasin or Arimidex, both of which will lower conversion to estrogen while also lowering SHBG. This study also gives us younger guys a good reason to stay lean on our cycles to keep estrogen conversion to a minimum.
J Clin Endocrinol Metab. 2010 Jun 9. [Epub ahead of print]
The Effects of Injected Testosterone Dose and Age on the Conversion of Testosterone to Estradiol and Dihydrotestosterone in Young and Older Men.
Lakshman KM, Kaplan B, Travison TG, Basaria S, Knapp PE, Singh AB, Lavalley MP, Mazer NA, Bhasin S.
Omnadren 250mg1ml JelfaBackground: During testosterone (T) therapy, T is partly converted to 17beta-estradiol (E2) and 5alpha-dihydrotestosterone (DHT). Effects of age, testosterone dose, and body composition on total and free E2 and DHT levels are unknown. Objective: We evaluated age and dose-related differences in E2 and DHT levels in response to graded doses of testosterone enanthate in young and older men. Methods: Fifty-one young (aged 19-35 yr) and 52 older (aged 59-75 yr) men completed treatment with monthly injections of a GnRH agonist plus randomly assigned weekly doses of testosterone enanthate (25, 50, 125, 300, or 600 mg) for 5 months. Results: During testosterone administration, total and free E2 levels increased dose-dependently (dose effect, P < 0.001) in both young and older men. Total and free E2 levels and E2:T ratios during T administration were higher in older than young men, but age-related differences in free E2 and free E2:T ratios were not significant after adjusting for testosterone levels, percentage fat mass, and SHBG. DHT levels and DHT:T ratios were dose-related but did not differ between young and older men. Mechanistic modeling of free hormone data revealed that the conversions of T to E2 and DHT were both consistent with saturable Michaelis-Menten kinetics. The in vivo Km values were estimated to be 1.83 nM for aromatase and 3.35 nM for 5alpha-reductase, independent of age. The Vmax parameter for E2 was 40% higher in older men than younger men, but Vmax for DHT was not significantly different between age groups. Conclusions: During im testosterone administration, E2 and DHT levels exhibit saturable increases with dose. The rate of whole body aromatization is higher in older men, partly related to their higher percentage fat mass, SHBG, and testosterone levels.
PMID: 20534765 [PubMed - as supplied by publisher]