Scientists from the Anton Dohrn Zoological Laboratory in Naples, Italy found that D-aspartic acid increased testosterone by 30 percent in human men, and by 51 percent in rats. Obviously, this caught the interest of fitness enthusiasts. We warned that the study did not measure the effects of D-aspartic acid on performance, muscle mass or strength, so we could not recommend it as an effective supplement for bodybuilders or power athletes. You should have listened to us. Australian scientists from the University of Western Sydney, led by Geoffrey Melville, found that daily supplementation of either three or six grams of D-aspartic acid decreased total and free testosterone in resistance-trained men, and had no effect on related hormones such as estrogen or sex-hormone binding globulin. We don’t know its effects on muscle mass or performance.
Source: Journal of the International Society of Sports Nutrition, 12: 15, 2015