Bodybuilders who take 6 g CLA a day synthesise more testosterone, according to a small human study published by Italians in 2012 in the Journal of Strength and Conditioning Research.
We recently wrote about an Italian animal study in which mice that did daily high-intensity endurance exercise synthesised more testosterone when they were given CLA. A year previously the same authors published the results of a human study on the effects of CLA on testosterone levels.
In that study the researchers tested the hypothesis that CLA supplementation induces the Leydig cells in the testes to produce more testosterone. The publication describes an in-vitro study using R2C Leydig cells from a rat. The longer the cells are exposed to CLA in a test tube, the more testosterone they produce. And the testosterone production increased the higher the CLA concentration.
The results of the in-vitro study are shown below.
The Italians then turned their attention to whether humans also produce more testosterone when they are given CLA. The researchers gave 10 highly trained male strength athletes – average age 27 – a daily dose of 6 g CLA for three weeks. Before and after the supplementation period the researchers got their subjects to do weight training and analysed the men’s blood before and after working out.
During another period of three weeks the men were given a placebo.
The researchers observed no effects of the CLA supplementation on the concentration of estradiol, cortisol or SHBG. They did discover though that the men synthesised more testosterone after working out as a result of CLA supplementation.
The Italians observed no change in strength or body composition.
“The results of the present study show that CLA may have an effect on testosterone synthesis, although only a potentially slight increase in total testosterone compared with the placebo was observed in physically active men”, the researchers conclude. “It means that CLA might be used as an ergogenic aid to increase the anabolic effect of a resistance exercise bout, but further research is needed to understand the physiological relevance of this slight effect on testosterone.”
Effect of conjugated linoleic acid on testosterone levels in vitro and in vivo after an acute bout of resistance exercise.
Macaluso F, Morici G, Catanese P, Ardizzone NM, Marino Gammazza A, Bonsignore G, Lo Giudice G, Stampone T, Barone R, Farina F, Di Felice V.
The purposes of the present study were to investigate the effect of conjugated linoleic acid (CLA) supplementation on testosterone levels in vitro on a cell line derived from Leydig cells (R2C) and in vivo in the blood of physically active subjects before and after a resistance exercise bout. In vitro R2C cells were treated with different CLA concentrations (0-30 ?M) for 24 and 48 hours. After treatment, supernatant media were tested to determine testosterone secretion. The CLA increased the testosterone secretion only after 48 hours. In vivo, 10 resistance-trained male subjects, in a double-blind placebo-controlled and crossover study design were randomized for 3 weeks of either 6 g·d?¹ CLA or placebo. Blood was drawn pre and post each resistance exercise bout to determine the total testosterone and sex hormone-binding globulin (SHBG) levels. No significant differences were observed for total testosterone or SHBG pre and post each resistance exercise bout; although after the resistance exercise bouts, total testosterone increased moderately (effect size = moderate), whereas after CLA supplementation, there was a large increase in total testosterone (effect size = large). CLA supplementation induced an increase in testosterone levels in Leydig cells in vitro after 48 hours but not in vivo before and after a resistance exercise bout. These findings suggest that CLA supplementation may promote testosterone synthesis through a molecular pathway that should be investigated in the future, although this effect did not have an anabolic relevance in our in vivo model.
PMID: 22614148 [PubMed – indexed for MEDLINE]