This is from a study that I previously missed: Hormonal response following a minor physiological stress induced by bleeding in a blood donor clinic was investigated in 134 humans with different blood groups. After venisection, serum cortisol concentration (mean +/- SD) was found highest in blood group A donors (455 +/- 217 nmol/L), followed by group B (364 +/- 206), AB (325 +/- 154) and O (297 +/- 110). In 14 subjects of blood group A compared to an equal number of blood group B subjects, mean plasma adrenaline level was higher in group A (0.23 +/- 0.09 nmol/L) than in group B (0.15 +/- 0.12) but the difference was not statistically significant. Blood group A individuals responded to a … Continue reading Blood group A individuals responded to a stressful situation with higher levels of cortisol, and possibly of adrenaline