The cost of coping: a cardio-neuro-metabolic risk for black South Africans?

Psychosocial stress is a contributing factor to cardiovascular disease. 1 An important way of investigating the mechanisms underlying this association is acute psycho-physiological stress testing, involving measurement of physiological responses to laboratory-induced stress. Psycho-physiological stress testing allows individual differences in responses to standardised stress to be evaluated and related to psychosocial and cardiovascular risk factors. Accumulating evidence has demonstrated associations of disturbed psycho-physiological responses with sub-clinical measures of atherosclerosis, hypertension and metabolic risk. The complex pattern of responding to stress is influenced by individual differences, such as coping style, race and ethnic-ity, genetic make-up, background stress, and lifestyle habits, which should be taken into account when interpreting results. For example, a unique interplay between cardiac and vascular responses in urban black Africans 2 is thought to contribute towards a heightened risk of hypertension in this group. Whether or not psycho-physiological risk markers provide prognostic information over and above that of established risk markers is not clear but adapting to or appraisal of an urban environment could add to heightened responses. There are, however, marked ethnic differences in cardio-vascular responses or reactivity (CVR) that may in part be explained by psychosocial factors. Black Africans 7,8 and African-Americans 4 normally and when exposed to stressful situations exhibit exaggerated CVR and a higher risk for the development of hypertension 1 in comparison to Caucasians. In three separate regions, including rural and urban black South Africans, results demonstrated increased vascular responses on exposure to the handgrip and cold pressor tests in urban participants compared to their rural counterparts. It is suggested that in urban Africans the physiological adaptation process is inclined to shift towards increased vascular responses and prevalence of hypertension. We might speculate that the individual who experiences emotional– social–cultural disruption in an urban environment is in a continuous state of hyper-vigilant coping and vascular sympathetic hyperactivity/overdrive through exaggerated CVR. Mental and chronic psychosocial stress triggers sympathetic nervous system (SNS) hyperactivity and has been shown to be associated with increased vascular responsiveness, pressure overload, hypertension and myocardial ischaemic risk. 5,7 Also, increased vascular and plasma renin responses seen in black African men further increase sympathetic activity through peripheral vascular hyper-responsiveness and higher blood pressure. This change to a high vascular resistance pattern accompanying hypertension predisposes to the development of left ventricular hypertrophy. In fact, studies show that African-Americans have greater left ventricular wall thickness than Caucasians, suggesting that increased peripheral vascular resistance may …