Effect of cocoa flavanols on microvascular function: a comparison in South Asians and White Europeans

Richardson, Sophie Rebecca (2024). Effect of cocoa flavanols on microvascular function: a comparison in South Asians and White Europeans. University of Birmingham. Ph.D.

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Abstract

South Asians (SAs) are an ethnic group with increased cardiovascular disease (CVD) risk, and SA women are at particular risk of coronary artery disease (CAD), which is attributed to microvascular endothelial dysfunction. There is also evidence of impaired endothelium-dependent dilator (EDD) responses in young SA men and women relative to White Europeans (WEs), which is considered predictive of future CVD. It has already been established that EDD responses in arterial vessels can be improved by cocoa flavanols (CFs). Thus, this project focussed on current evidence of whether dietary CFs can improve microvascular function and tested experimentally whether microvascular responses differ between young WE and SA women, and the effect of an acute CF intervention on these responses.
A systematic review of the literature indicated that consumption of CFs improved microvascular responses in several different tissues, but these studies were mostly performed in men or mixed gender groups with wide age ranges. Experimental recordings using venous occlusion plethysmography and near-infrared spectroscopy (NIRS) to monitor forearm blood flow (FBF) showed that reactive hyperaemia (RH) and exercise hyperaemia (EH), the vasodilator responses evoked following release of arterial occlusion and by rhythmic handgrip contractions respectively, were impaired in young SA, compared to WE women. In addition, NIRS recordings suggested that microvascular regulation of tissue oxygenation was impaired in SA women. However, there was no effect of CFs on RH, or EH in either WE or SA women. This suggests that CFs are less effective in women than in men at augmenting EDD responses.
In addition, mental stress induced by a mental arithmetic task, evoked forearm vasodilation in half of women from each ethnic group, but vasoconstriction in the rest, suggesting that the muscle vasodilation was blunted in a similar proportion of WE and SA women. When grouped according to the direction of their response to mental stress, CFs increased FBF in vasoconstrictors, but not vasodilators, consistent with CFs augmenting nitric oxide-dependent vasodilation, which is impaired in vasoconstrictors. Given that exaggerated vasoconstrictor responses to mental stress predict future hypertension and CVD, the novel finding that CFs attenuated vasoconstriction in some women raises the possibility that dietary CFs may help to limit CVD risk in this group.
Finally, a comparison of diet and lifestyle between a larger population of WE and SA men and women showed that SAs had lower physical activity levels, and consumed fewer portions of foods associated with improving vascular function, including flavonoids, than WEs. This suggests that lifestyle factors, including diet, may at least partly explain the impaired EDD responses of young SA relative to WE women, and are likely to increase their risk of future CVD.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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