In randomized controlled trials (RCTs) of phosphatidylserine (PS) in athletic populations, PS did not consistently improve the outcomes examined.
A pair of 2006 RCTs from a team of UK researchers tested PS supplementation in cycling and downhill running. The participants in the PS groups in both studies took a large dose of PS (750 mg) for 10 days before the exercise bout. In the cycling study, time to exhaustion in the PS group improved significantly compared to that of the placebo group. The increase in the PS group was dramatic — from nearly 8 minutes to nearly 10 minutes. No significant differences were found in any of the other outcomes the study measured, including lower-intensity performance, fatigue levels, and serum cortisol levels.[1] The second study didn't report on the participants' time to exhaustion, but focused on muscle soreness and biomarkers of muscle damage and exercise-induced inflammation and oxidative stress. The study found no significant differences between the participants who received PS and those who received a placebo.[2]
Unlike the 2006 cycling study, which found no significant difference in cortisol, a 2008 crossover study of PS supplementation and cycling found that participants' post-exercise cortisol area under the curve was lower after PS supplementation. The study found no significant difference in the other outcomes. This RCT looked at the participants' serum cortisol, lactate, testosterone and growth hormone after a bout of moderate-intensity to high-intensity cycling, conducted after 10 days of supplementation with either 600 mg of PS or a placebo.[3] Another crossover study, this one in resistance-trained young men, also found no significant differences in post-exercise mood, serum cortisol levels, or serum testosterone levels between participants who had taken 400 mg of PS for 14 days and those who had taken a placebo. However, participants in the PS group did perform better on 1 of 3 metrics related to performing simple math problems quickly.[4]
The participants who took a combined PS (400 mg) and caffeine (100 mg) supplement for 2 weeks reduced their fatigue ratings immediately after resistance training, compared to a placebo. However, caffeine is known to reduce fatigue ratings,[5] so it is difficult to say how much PS contributed. Outcomes whose improvements could have more clearly been attributed to PS, such as mood and cognition, were not improved with supplementation compared to a placebo.[6]