A membrane phospholipid with a signalling role
Phosphatidylserine (PS) is a phospholipid that sits mainly on the inner leaflet of cell membranes, including those of neurons. There it contributes to membrane integrity and helps anchor and activate signalling proteins. When PS moves to the outer leaflet, it acts as a recognition signal, for example during the clearance of dying cells, which illustrates how tightly its location is regulated.
Supplemental PS today is usually derived from soy or sunflower lecithin, after earlier products were made from bovine cortex.
The cortisol and stress-response hypothesis
PS has been studied for blunting the cortisol response to acute stress, including exercise stress, and some small trials report a dampened rise. The effect is modest and the literature is limited, so this is best described as a plausible mechanism rather than a guaranteed outcome, and PS does not treat clinical stress or anxiety disorders.
This is general educational information, not medical advice. If you are considering PS for stress, mood, or memory concerns, discuss it with a qualified professional rather than relying on a single figure or claim.