But I'm not more aggressive—a behavior change often tied to testosterone. That's not surprising to Robert Sapolsky, ., a neuroendocrinologist at Stanford University and a leading researcher on stress and behavior. "It's really not the case that testosterone 'causes' aggressive behavior," he says. "Instead, it makes the brain more sensitive to social cues that trigger aggression. And in support of that, a guy's testosterone level isn't a very good predictor of how likely he is to be aggressive."
In a 2011 randomized controlled study, researchers recruited 54 healthy men whose mean 25(OH)D levels were in the deficiency range for a year-long intervention. They divided the subjects into two groups. The first group of 23 men had an average serum 25(OH)D of nmol/L and took a daily placebo. The second group of 31 men had an average serum 25(OH)D of nmol/L and took a daily 3332-IU vitamin D supplement. After the trial was finished, the researchers observed a significant increase in total testosterone from nmol/L to nmol/L in the supplement group. 19 In contrast, there were hardly any changes in testosterone concentrations in the placebo group. 19 These findings suggest that men deficient in vitamin D who take a proper vitamin D supplement may fix low levels of low testosterone.
Now this is a remarkable change if you think about it. The "concentration" of testosterone and estrogen - estradiol is what really counts - changed by 24% from just one lifestyle change. Imagine what could happen as you pile on some of the other Testosterone Increasing Techniques and Estrogen Lowering Strategies that I have mentioned on the web site. There is no reason that you cannot dramatically improve your ratio of testosterone to estradiol (unless you happen to be training for the Olympics with a professional trainer).