ACUTE EFFECTS OF DIETARY NITRATE SUPPLEMENTATION IN POSTMENOPAUSAL WOMEN

Open Access
Author:
Kim, Jin-Kwang
Graduate Program:
Physiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 06, 2016
Committee Members:
  • David Nathan Proctor, Dissertation Advisor
  • James Anthony Pawelczyk, Committee Chair
  • Penny Margaret Kris-Etherton, Committee Member
  • Connie Jo Rogers, Committee Member
  • Penny Margaret Kris-Etherton, Outside Member
Keywords:
  • cardivascular
  • Aging
  • dietary nitrate supplementation
  • beetroot juice
  • women
Abstract:
Women’s arteries are exposed to adverse age- and perimenopause-associated changes in cardiovascular risk factors, leading to accelerated stiffening of central arteries, attenuated functional (exercise) vasodilation, and exaggerated blood pressure reactivity after menopause. Unfortunately, traditional pharmacological management of blood pressure has not been highly effective in older women, and there are only a few low risk, estrogen-based therapies for improving vascular health in this age group. Consequently, there is a clinical need to investigate novel interventions for vascular health in post-menopausal women, particularly dietary interventions that have the potential to augment nitric oxide bioavailability and lower their blood pressure. The studies comprising this dissertation tested the ability of nitrate-rich beetroot juice (140 ml of beetroot juice containing 0.6g of nitrate) to raise circulating concentrations of nitrite (NO2-) and favorably influence central (aortic) hemodynamics and arterial stiffness at rest (study 1), ischemic forearm exercise tolerance and perceived effort (study 2), and muscle metaboreflex control of blood pressure (study 3) in normotensive, metabolically healthy post-menopausal women (57-64 yr; n = 9). A double-blind, placebo-controlled (BRnitrate vs. BRplacebo; IND#119978), cross-over study design was used, with a 7-day washout period between treatments, and standardized pre-visit instructions to minimize between-visit variation in plasma [NO2-]. Compared to responses observed during the BRplacebo visit, BRnitrate consumption raised plasma [NO2-], reduced resting systolic blood pressures (brachial and aortic), delayed the initial rise in perceived exertion during graded ischemic exercise, and attenuated the peak increase in mean arterial pressure during maximal engagement of the exercise pressor reflex (all p < 0.05). Non-significant effects were observed for resting arterial stiffness (pulse wave velocity; p = 0.33), ischemic forearm exercise time to fatigue (p = 0.13) and diastolic blood pressures during metaboreflex isolation (p = 0.18). Collectively, these results provide the first evidence that acute dietary nitrate supplementation has beneficial cardiovascular effects in healthy older women at rest and during a condition known to promote the conversion of NO2- to nitric oxide (ischemic forearm exercise). These studies also raise a new series of questions related to the mechanisms by which dietary nitrate may benefit cardiovascular health and exercise tolerance/blood pressure reactivity in older women, and support the pursuit of larger scale trials of dietary nitrate supplementation to determine whether these effects are in fact clinically significant and sustainable.