Research on Nitrate-Rich Vegetables and Blood Pressure

Introduction to Hypertension

High blood pressure, known medically as hypertension, impacts millions globally, with approximately 75 million affected in the United States alone. Maintaining healthy blood pressure levels is crucial to prevent hypertension, as it is a leading contributor to heart attacks and strokes. Inorganic nitrate and nitric oxide play vital roles in cardiovascular health, with inorganic nitrate converting to nitric oxide, which helps dilate blood vessels. Increasing nitrate intake can enhance nitric oxide production in the body.

The Nitrate-Rich Vegetable Study

A recent study published in the American Journal of Clinical Nutrition investigated whether consuming nitrate-rich vegetables could reduce high blood pressure in individuals with prehypertension or untreated grade 1 hypertension. Conducted in Australia, the study involved 30 participants aged between 21 and 75 years.

This randomized, controlled crossover trial featured three distinct four-week treatment periods interspersed with four-week rest phases, culminating in a total of 24 weeks. Participants followed one of three treatment protocols: consuming high-nitrate vegetables, low-nitrate vegetables, or no additional vegetables during the control phase.

Methodology

Before and after each treatment period, researchers collected data on participants’ height, weight, waist circumference, and hip circumference. They conducted various assessments, including electrocardiograms, blood pressure tests, fasting blood tests, fasting saliva tests, fasting urine tests, medical examinations, and food-frequency questionnaires. Arterial stiffness was also evaluated pre- and post-treatment. Participants reported any medications or supplements they were taking and provided detailed medical histories.

During the study, participants made minor dietary adjustments, consuming mixed vegetable juices at breakfast and dinner. The high-nitrate treatment required a daily intake of 150mg of nitrate, while the low-nitrate treatment involved 22mg. In the control period, participants consumed water blended with a quarter of an orange and eight grams of maltodextrin, resulting in a nitrate intake of 6mg. Food diaries confirmed adherence to the treatment protocols, and nitrate and nitrite digestion was monitored through blood, saliva, and urine samples.

Results of Nitrate-Rich Vegetable Consumption

While participants showed an increase in overall nitrate, nitrite, and carotenoid levels, the study concluded that an increased intake of nitrate-rich vegetables did not lead to a reduction in blood pressure or changes in arterial stiffness. The authors noted that multiple trials have explored this hypothesis, yielding inconsistent results. Some studies reported decreased blood pressure, while others found no significant changes.

Factors contributing to these differing outcomes may include the amount of nitrate consumed, baseline nitrate levels, prior vegetable intake, and the participants’ age and health status. The authors of this study identified potential reasons for the lack of blood pressure reduction. If participants had already consumed sufficient nitrate before the study, additional nitrate may not have been effectively metabolized. Furthermore, a 12-hour fasting period prior to blood, saliva, and urine sampling could have influenced nitrate concentrations.

Despite these considerations, the extended duration of the study and the absence of participants on antihypertensive medications add to its reliability and uniqueness.

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References

Blekkenhorst C, Lauren, et al. Nitrate-rich vegetables do not lower blood pressure in individuals with mildly elevated blood pressure: A 4-wk randomized controlled crossover trial. ASN. 2018. 107: 894-908. https://doi.org/10.1093/ajcn/nqy061
Centers for Disease Control and Prevention: Blood Pressure. 2018, https://www.cdc.gov/bloodpressure/index.htm. Accessed 7 June 2018.