Phosphatidylserine (PS) is a phospholipid found in high concentrations in brain tissue and is involved in cellular function, particularly in neurons. Its use to support the "Cortisol body system" typically refers to its purported ability to modulate the body's stress response, specifically by influencing cortisol levels. Several clinical studies have investigated the effects of phosphatidylserine supplementation on cortisol, particularly in response to acute physical or psychological stress. A number of randomized, placebo-controlled trials have shown that PS supplementation (generally in doses of 300-800 mg/day) can attenuate the rise in cortisol following intensive exercise or mental stress in healthy adults.

For example, a double-blind study by Monteleone et al. (1992) found that PS supplementation significantly blunted the ACTH and cortisol response to physical stress. Other studies, such as those by Fahey et al. (1998) and Kingsley et al. (2006), have shown reductions in exercise-induced cortisol increases. However, not all studies have found positive effects, and there is variability in dosing, duration, and populations studied. The mechanism is not fully understood but may involve modulation of hypothalamic-pituitary-adrenal (HPA) axis activity.

Overall, while there is some scientific evidence to support phosphatidylserine's use in modulating cortisol responses to acute stress, the evidence is moderate and not universally consistent. Further large-scale, long-term studies are needed for definitive conclusions.