See Also

Stress (roughly the opposite of relaxation) is a medical term for a wide range of strong external stimuli, both physiological and psychological, which can cause a physiological response called the general adaptation syndrome, first described in 1936 by Hans Selye in the journal Nature.

The chemistry of stress

Under circumstances of physiological or emotional stress, the body protects itself by shifting the relative balance of our nervous system and by rapidly secreting specific stress hormones such as cortisol, adrenaline (sometimes called epinephrine) and noradrenaline (sometimes called norepinephrine). These effects are not ideal over the long term.

The adrenal glands are an extension of the sympathetic nervous system. In response to stress these glands release several different chemicals into the blood stream. These messengers provide another level of communication between the nervous system, the hormonal system, and other internal systems to provide further direction as to how they should act in response to stress.


The first class of the messenger molecules made by the adrenal glands are catecholamines. There are two catecholamines released from the adrenals in response to stress: Epinephrine (commonly called adrenaline) and norepinephrine. This response is very useful under some circumstances. But a prolonged duration of time in this mode will come at a cost.

Although blood group A individuals respond to stress by releasing a lot of adrenaline, they also eliminate it very quickly. Blood group O appear to have more difficulties with catecholamines; if they produce a any sizeable amount in response to stress, it will take them a while to eliminate them and their effects. This may be the result of the amorph aspects of the O genotype and its influence via gene linkage on the actions of dopamine beta hydroxylase, an enzyme that shares an adjacent locus. (1)

Investigation of the relationship between ABO blood groups (ABO BG) and Type A behavior pattern (TABP) was performed. CH and TH + CH scores in individuals with blood type A and type A personality were significantly lower (P less than 0.01). The values of TH-CH scores among tested people were of no statistical significance (P greater than 0.05). Moreover, nearly half of the examinees (41.32%) had higher CH score and the distribution of the individuals was obviously different in statistics (P less than 0.005). In addition, L score of examinees with blood type A and type B personality was relatively lower. (2)

Consistent correlations have been found between physical dysfunctional states and blood factors. Some of these disorders have possible psychosomatic components (eg, duodenal ulcer, myocardial infarction). This study focused on the relationship between blood types and various indices of behavior patterns (eg, type A behavior scores, anger ratings) in young patients who had had an initial myocardial infarction. Patients with blood type O scored significantly higher on type A behavior scales and related indices than those having blood type A. Those with blood group B responded on several scales between those with types A and O. We discuss the utility of blood groupings in future research in the prediction of myocardial infarction, methodologic limitations, the relationship of these results to temperament studies, Jenkins Activity Survey subtest patterns, anti-H reactivity pattern, and hypotheses relating blood factors and behavioral traits in patients with psychosomatic disorders. (3)


Another critical hormone to consider is cortisol which is also made and released from your adrenal glands. Cortisol is in a class of chemicals called glucocorticoids. Most people have actually used a glucocorticoid at some point in time. Medicines like hydrocortisone or prednisone are examples of these glucocorticoids.

While the catecholamines can be thought of as more of a short-term solution to stress, cortisol is more of a long-term response. Cortisol is a catabolic hormone, meaning it will function to break down muscle tissue and convert the proteins from this muscle tissue into energy. This hormone is often portrayed as the enemy of body builders since it acts to break down their hard-earned gains in muscle mass.

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 stressful situation with higher levels of cortisol, and possibly of adrenaline. These observations tend to support findings of previous studies demonstrating a high risk of diseases related to stress (coronary heart diseases and gastrointestinal diseases), in men with A blood group. (4)

Cortisol is considered to be such a reliable indicator of stress upon a system that many physiologists define stress as an event that elicits increased levels of cortisol. These include exposure to cold, starvation, bleeding, surgery, infections, pain or injuries, and too much exercise just to name a few. Even your mental state can induce the increase of this hormone. A critical, but often overlooked, piece of the puzzle influencing the release of cortisol to stress is actually your blood type. But before looking at this connection lets explore cortisol and stress a bit further. It is in the arena of cortisol that blood type A's are hit the hardest and blood type O's tend to be spared.

Past research has associated ABO blood type and mental stress with cardiovascular risk. The effects of blood type (A vs. O) coupled with a mirror drawing stressor on very low density lipoprotein toxicity-preventing activity (TxPA) and plasma cortisol levels have been studied. Exposure to the stressor significantly decreased TxPA and increased cortisol for the total group of 25 older adult males. However, the stress response patterns of the 15 blood type A males were different from those of the 10 type O subjects. The blood type A group had higher initial levels of TxPA and cortisol as well as quicker stress recovery rates than the type O group. ABO blood type may be an important behavioral hematologic variable to assess in studies concerning biochemical stress response or cardiovascular risk.(5)


Determination of ABO blood types was carried out in 72 (35 female and 37 male) patients with obsessive-compulsive neurosis, 73 (35 female and 38 male) patients with phobic neurosis, 75 (54 female and 21 male) patients with hysteria and a random sample of 600 individuals (268 female and 332 male) drawn from the general population. Results provide evidence of: (1) a positive association between obsessive-compulsive neurosis and blood type A and a corresponding negative association between the former and blood type O; (2) a positive association between phobic neurosis and blood type O and a corresponding negative association between the former and blood type A, and (3) a positive association between hysteria and blood type A and a corresponding negative association between the former and blood type O. Moreover, sex does not appear to modify the ABO blood type distribution in our patients with obsessive-compulsive neurosis, phobic neurosis or hysteria. These findings might be considered as supporting the view that hereditary factors in the neurotic individual may influence the clinical form of his neurosis. (6)

Platelet Mono Amine Oxidase (MAO)

The association between the two genetic markers of affective disorders, ABO blood group system and platelet MAO (monoamine oxidase) activity was studied in 70 healthy young males. The platelet MAO activity of subjects with blood type O was significantly lower than that of subjects with blood type A and with blood types A + B AB + B together. This finding could constitute a "bridge" between the two genetic approaches to affective disorders. (7)


1. Sherrington R, Curtis D, Brynjolfsson J, Moloney E, Rifkin L, Petursson H, Gurling H. A linkage study of affective disorder with DNA markers for the ABO-AK1-ORM linkage group near the dopamine beta hydroxylase gene. Biol Psychiatry 1994 Oct 1;36(7):434-442

2. Mao X, Xu M, Mu S, Ma Y, He M. Study on relationship between human ABO blood groups and type A behavior pattern. Hua Hsi I Ko Ta Hsueh Hsueh Pao 1991 Mar;22(1):93-96

3. Neumann JK, Chi DS, Arbogast BW, Kostrzewa RM, Harvill LM. Relationship between blood groups and behavior patterns in men who have had myocardial infarction. South Med J 1991 Feb;84(2):214-218

4. Locong AH, Roberge AG. Cortisol and catecholamines response to venisection by humans with different blood groups. Clin Biochem 1985 Feb;18(1):67-69

5. Neumann JK, Arbogast BW, Chi DS, Arbogast LY. Effects of stress and blood type on cortisol and VLDL toxicity preventing activity. Psychosom Med 1992 Sep;54(5):612-619

6. Rinieris P, Rabavilas A, Lykouras E, Stefanis C. Neuroses and ABO blood types.Neuropsychobiology 1983;9(1):16-18

7. M, Bagdy G, Rihmer Z, Kulcsar Z. Reduced platelet MAO activity in healthy male students with blood group O. Acta Psychiatr Scand 1983 Feb;67(2):130-134