A Summary of the article on “Effect of Spinach, a High Dietary Nitrate Source, on Arterial Stiffness and Related Hemodynamic Measures: A Randomized, Controlled Trial in Healthy Adults”
Background
The article, “Effect of Spinach, a High Dietary Nitrate Source, on Arterial Stiffness and Related Hemodynamic Measures: A Randomized, Controlled Trial in Healthy Adults” by Jovanovski et al. (2015) published in Clinical Nutrition Research in July 2015, investigated the impact of dietary nitrate from spinach on vascular health. Authored by Elena Jovanovski and colleagues, the study aimed to determine if short-term consumption of spinach could affect arterial stiffness, and central and peripheral blood pressure (BP). This research builds on the understanding that diets rich in fruits and vegetables reduce cardiovascular risk, with recent attention on high-nitrate vegetables as a source of vasoprotective nitric oxide (NO). Given that hypertension affects nearly a billion people globally, and dietary modifications are a primary treatment, understanding specific dietary components like nitrate is crucial. Importantly, measures like augmentation index (AI), an indicator of arterial stiffness, and central BP are considered more closely associated with cardiovascular events than brachial BP.
Methods
The study employed a randomized, controlled, single-blinded, crossover design with 27 healthy participants aged 18-50. Each participant underwent two 7-day intervention phases, separated by a 1-week washout period. The interventions consisted of either a high-nitrate spinach soup (approximately 845 mg nitrate/day) or a low-nitrate asparagus soup (control, approximately 0.6 mg nitrate/day). The soups were matched for energy, macronutrients, and key minerals like potassium and sodium, with nitrate content being the primary difference. Participants were blinded to the intervention. On Day 1 and Day 7 of each phase, vascular measurements, including augmentation index adjusted for 75 beats per minute (AI75), central BP, and brachial BP, were taken over 180 minutes post-consumption, following a 10-12 hour fast.
Results
The findings revealed several promising hemodynamic benefits. On Day 1, the high-nitrate spinach intervention led to a significant reduction in AI75 of -6.54 ± 9.7% at 180 minutes post-consumption relative to baseline, and -5.72 ± 10.8% compared to the low-nitrate control (p = 0.01). After 7 days, the high-nitrate intervention sustained this reduction in AI75 from baseline (-6.93 ± 8.7%, p < 0.001), indicating no development of tolerance. Furthermore, following 7-day supplementation, the high-nitrate spinach significantly reduced central systolic BP by -3.39 ± 5.6 mmHg (p = 0.004) and central diastolic BP by -2.60 ± 5.8 mmHg (p = 0.028) at 180 minutes when compared to the low-nitrate control. Brachial systolic BP also showed reductions in the high-nitrate group compared to the low-nitrate intervention on Day 7. Mild bloating was reported in both groups, but no other adverse events occurred.
Conclusions
The study suggests that dietary nitrate from spinach contributes to beneficial hemodynamic effects by potentially increasing NO production via the oxygen-independent nitrate-nitrite-NO pathway, which is particularly relevant in cardiovascular disease where oxygen-dependent pathways may decline. The observed effects at 180 minutes align with the pharmacokinetics of orally administered dietary nitrate and its bioconversion to nitrite by oral microbiota. Interestingly, the low-nitrate asparagus control also showed an unexpected reduction in AI75 on Day 7 compared to Day 1, potentially due to other bioactive components like steroidal saponins, which are known to have vasodilatory properties. The authors note that the observed changes in AI75 likely reflect functional alterations in vascular smooth muscle tone rather than structural changes, given the study’s short duration. The study also addresses concerns about dietary nitrate and cancer risk, highlighting that nitrate from vegetables has been associated with a decreased risk of cancer.
Limitations of the study include reliance on self-reported compliance and the absence of plasma nitrate level measurements. While the study could not attribute the effects to a single bioactive compound, the authors emphasize the importance of understanding the overall health effects of whole, nutrient-dense vegetables like spinach. In conclusion, this preliminary study demonstrates the promising potential of dietary nitrate from whole foods like spinach to improve vascular health by reducing arterial stiffness and central BP in healthy individuals. These findings underscore the importance of dietary and lifestyle modifications in the prevention and management of cardiovascular disease.
References
Jovanovski, E., Bosco, L., Khan, K., Au-Yeung, F., Ho, H., Zurbau, A., Jenkins, A. L., & Vuksan, V. (2015). Effect of Spinach, a High Dietary Nitrate Source, on Arterial Stiffness and Related Hemodynamic Measures: A Randomized, Controlled Trial in Healthy Adults. Clinical Nutrition Research, 4(3), 160. https://doi.org/10.7762/cnr.2015.4.3.160
This post is based on Open Access research and is for informational purposes only.
