Effect Of Diet On Vascular Health In Type 2 Diabetes And Community-dwelling Adults
Open Access
- Author:
- Sauder, Katherine Ann
- Graduate Program:
- Biobehavioral Health
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 04, 2014
- Committee Members:
- Sheila Grace West, Dissertation Advisor/Co-Advisor
Sheila Grace West, Committee Chair/Co-Chair
Penny Margaret Kris Etherton, Committee Member
Jan Ulbrecht, Committee Member
David Nathan Proctor, Committee Member - Keywords:
- Cardiovascular disease
nutrition
diabetes
metabolic syndrome
blood pressure
endothelial function
arterial stiffness - Abstract:
- Cardiovascular disease (CVD) is the leading cause of death in the United States. Lifestyle modification, including dietary changes, continues to be the first line of therapy for risk management. While notable progress has been made in identifying foods and nutrients that optimize health, it remains unclear as to what eating patterns are most effective at reducing risk in vulnerable populations. The purpose of this dissertation is to examine the relationship between diet and vascular risk factors in two high-risk populations: individuals with type 2 diabetes and older adults. Additionally, it will examine the reliability of a novel method of measuring vascular health that has the potential to improve risk assessment in the medical clinic. The first study in this dissertation evaluated the effects of nut consumption on blood pressure, systemic hemodynamics, heart rate variability, and endothelial function in adults with type 2 diabetes. Cardiovascular disease is the leading cause of death in this population, and interventions to reduce risk are urgently needed. We enrolled 30 adults with type 2 diabetes in a randomized, crossover, controlled-feeding study. After a 2-week baseline period, participants consumed a low-fat control diet (27% fat) and a moderate-fat pistachio diet (33% fat) containing pistachios (20% of daily energy) for 4 weeks each. Following each diet period, we assessed systemic hemodynamics and heart rate variability at rest and during acute mental stress, endothelial function, and, in a subset of participants (n=21), 24-hour ambulatory blood pressure. There was no difference between treatments in blood pressure at rest and during mental stress; however, total peripheral resistance was significantly reduced by approximately 4% following the pistachio diet and did not change following the control diet. Furthermore, 24-hour ambulatory systolic blood pressure, which is a better predictor of target organ damage than resting blood pressure, was significantly reduced by 3.5 mmHg following the pistachio diet. Several measures of heart rate variability were improved following the pistachio diet, and there was no difference between the treatments on endothelial function. This study demonstrates that, for individuals with type 2 diabetes, consuming a moderate-fat diet that includes pistachios improves multiple cardiovascular risk factors. The second study in this dissertation examined whether adherence to the 2010 Dietary Guidelines for Americans is independently associated with endothelial dysfunction and arterial stiffness in a cross-sectional sample of adults from the Framingham Heart Study. There is strong evidence from intervention studies that diet is related to vascular health, but the majority of these studies have tested individual foods or nutrients and relied on small samples of mostly younger adults. The effect of overall diet quality, as defined by public health recommendations, on measures of vascular health is unknown. This study included diet and vascular data previously collected in 6020 adults in the Framingham Heart study. Diet quality was quantified with the 2010 Dietary Guidelines for Americans Index (DGAI-2010), endothelial dysfunction was assessed via brachial flow-mediated dilation, and arterial stiffness was assessed via carotid-femoral pulse wave velocity. Regression analyses were used to determine whether DGAI-2010 scores were independently associated with vascular health. Baseline brachial mean flow velocity significantly decreased with increasing DGAI-2010 scores (P=0.002) and hyperemic mean flow ratio significantly increased with increasing DGAI-2010 scores (P=0.02). Augmentation index significantly decreased with increasing DGAI-2010 scores; age-stratified analyses revealed that this relationship was statistically significant only in older adults (>50 years). Diet was not significantly related to measures of endothelial dysfunction. Our results suggest a link between diet quality and vascular health and as such may be useful for designing interventions to treat or prevent age-related vascular decline. The third study in this dissertation assessed the test-retest reliability of a novel method of measuring endothelial dysfunction. Peripheral arterial tonometry (PAT) is a promising method for non-invasive assessment of endothelial dysfunction that is operator-independent, easily standardized between laboratories, and FDA-approved for risk assessment in medical clinics. Furthermore, given the increased risk of diabetes and CVD in adults with the metabolic syndrome, it is important to verify the reliability of PAT in the metabolic syndrome and to provide population-specific power and sample size estimates that can guide clinical trial design. This study included 20 adults with the metabolic syndrome who completed 5 PAT tests each separated by 1 week. The PAT-derived index of endothelial dysfunction (the reactive hyperemia index, RHI) showed robust repeatability (intra-class correlation = 0.74), and was not related to daily fluctuations in glucose and insulin. We show that a parallel arm study powered at 0.90 would require 22 participants to detect an absolute change in RHI of 0.40 units (equal to ~25% change in this sample), whereas a crossover study would require only 12 participants. These results indicate that PAT can be used to assess endothelial dysfunction in adults with the metabolic syndrome as reliably as in healthy subjects. In conclusion, dietary modification is a key element of CVD prevention. This dissertation provides evidence that a specific food (pistachios) and health dietary pattern (the Dietary Guidelines for Americans) may reduce risk in vulnerable populations. It also demonstrates the reliability of a novel, non-invasive method of measuring vascular endothelial dysfunction in a population with elevated risk. These findings can help researchers and clinicians develop interventions to reduce the burden of CVD in the United States and globally.