Double product and psychological distress in a bi-ethnic urban South African cohort : the SABPA study
Schutte, Christiaan Ernst
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Argument: Hypertension contributes to the development of cardiovascular diseases. Several factors contribute to the development of hypertension, such as obesity, alcohol abuse and psychological distress. Black Africans suffer from hypertension due to life-style changes or urbanisation which can possibly increase psychological distress. Chronic distress can trigger sympathetic hyperactivity to activate the hypothalamic-pituitary-adrenal axis (HPAA) stress channel which releases the stress hormone, cortisol, which can increase cardiometabolic risk during chronic conditions. Double product (DP) is ideal for measuring workload of the heart since it is the product of systolic blood pressure and heart rate which serves as an index of oxygen consumption. DP, which also incorporates heart rate, can have a stronger relation with metabolic factors where an increased heart rate can contribute to increased cardiometabolic risk during sympathetic over-activity. Aim: We aim at assessing associations between DP, silent myocardial ischemia (ST), cortisol and Adrenocorticotropic hormone (ACTH) in different ethnic sex groups, and at assessing associations between DP, cortisol and ST during psychological distress. Methodology: Our sub-study is founded on the Sympathetic activity and Ambulatory Blood Pressure in Africans (SABPA) study (2008-2009). The sample group comprised a Socio-economically matching population of 409 teachers of the Dr Kenneth Kaunda Education District in North-West Province of South Africa. Cortisone users (n=3), participants diagnosed with atrial fibrillation (n=16) and clinically diagnosed diabetes (n=12) were excluded. The final group comprised 378 individuals which consisted of 92 Black men, 94 Black women, 94 White men and 102 White women. Ambulatory blood pressure, electrocardiogram and physical activity level values were obtained during the 48-hour clinical data collection process. Fasting Blood samples were collected and included gamma glutamyl transferase, high sensitivity C-reactive protein (CRP), cotinine, HbA1c, cortisol and corticotropin samples. Independent t-tests and Chi-square tests were used with a view to compare Black and White groups, followed by a covariance analyses (ANCOVA). ANCOVAs were corrected for a priori variables (age, waste circumference, physical activity, gamma glutamyl transferase and cotinine). Independent associations between DP, silent ischemic incidents, cortisol and cardiometabolic risk markers were determined in the total cohort as well as in moderate to severely depressive ethnic gender groups. Results: Blacks demonstrated a poorer cardiovascular profile with higher blood pressure values, an increased heart rate, higher HbA1c levels, more ischemia as well as more low-grade inflammation (CRP > 3 mg/l) than the White gender group. Lower cortisol as well as higher ACTH values occurred in Black men than in other ethnic and gender groups. Waist circumference was lower in Black men and higher in Black women than in White men and women. Stratification on race x gender groups showed low cortisol and higher ACTH as well as more silent ischemia in Black men, but in none of the other groups. The Black women, similar to the black men, showed higher ACTH values than was the case with White women. Associations were found between waist circumference and double product in Black men [Adj R2 0.36; β 0.35 (0.17,0.51); p<0.001], Black women [Adj R2 0.11; β 0.27 (0.06,0.48); p=0.014]; White men [Adj R2 0.33; β 0.52 (0.35,0.69) p<0.001]; and in White women [Adj R2 0.36; β 0.37 (0.10,0.60); p=0.007]. Following stratification of the participants in moderate and severely depressive (MDED) and non-MDED groups, associations were demonstrated between DP and silent ischemia (ST) [Adj R2 0.19; β 0.41 (0.40,0.42); P = 0.025] as well as between ST and cortisol [Adj R2 0.19; β 0.37 (0.25,0.48); P = 0.043] only in Black men. Conclusion: Emotional distress can facilitate autonomous dysfunction or sympathetic hyperactivity in the current Black male group. Hence, during chronic distress cortisol levels can influence double product negatively. It can increase the occurrence of ST, which increases down-regulation of the HPA axis and risk for cardiovascular disease. This indicates that higher emotional demands can influence cardiometabolic health where susceptibility to emotional distress can be an underlying factor for the observed differences in the group of Black men.
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