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Strawberry Consumption Improves Vascular Health Parameters in Adolescent Males

April 21, 2020
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The 2019 Berry Health Benefits Symposium resulted in a collection of papers recently published in the journal Food & Function. Among the papers was "Effects of short-term consumption of strawberry powder on select parameters of vascular health in adolescent males" authored by Roberta Holt, Carl Keen, and their team at University of California, Davis. Here is a brief summary of their study as well as implications for practical applications and future strawberry nutrition research.

Studying Cardiovascular Health in Childhood

Although cardiovascular disease (CVD) is perceived as a disease manifested in adulthood, mothers with hypercholesterolemia during pregnancy may pass on fatty streaks and risk for CVD to their children. Further, due to the increased CVD risk factors in children such as obesity and insulin resistance, the American Heart Association has proposed targeting children through young adults to help achieve their 2020 Impact Goal of reducing vascular disease and stroke deaths by 20%. This gave the research team justification for studying vascular function in a youth population. Polyphenol-rich foods have an inverse relationship with CVD risk. Strawberries are a powerful source of polyphenols, particularly pelargonidin, flavonols, ellagic acid, and ellagitannins. They are also a source of dietary nitrate, the precursor for nitric oxide known for its vasodilation effects.

Research Design

The research team designed a randomized, controlled, double-blind, crossover trial to assess whether the acute (one hour) or short-term (one week) consumption of a freeze-dried strawberry powder could influence vascular health in adolescent males. The participants had a higher CVD risk due to their elevated adiposity (>75th percentile for age and sex).

Holt et al hypothesized that vascular function would increase following the intake of strawberry powder compared to a control powder. Microvascular function as measured by peripheral arterial tonometry (PAT), platelet reactivity, and plasma nitrate and nitrite concentrations were assessed before and after the one-week daily consumption of 50g of strawberry powder or an isocaloric, macronutrient-matched control powder that was devoid of polyphenols. The powders were divided into two 25g servings. The teenagers were instructed to mix the powder in water, consuming one packet at breakfast and the other at dinner.

Twenty-five males aged 14–18 years old were enrolled in the trial. The mean age was 16 years, and the participants on average were healthy with normal blood pressures, fasting lipid profiles, and fasting blood glucose levels.

PAT was assessed after an overnight fast and one hour after consuming the assigned powder. The measurement provided the data for: (1) reactive hyperemia index (RHI), (2) Framingham RHI (fRHI), an index associated with cardiovascular risk factors, (3) augmentation index (AIx), a useful assessment of vascular function in children, (4) platelet reactivity assessed by flow cytometry, and (5) total plasma nitrate/nitrite.

Results

An initial analysis demonstrated that neither short-term (seven-day) nor acute strawberry powder intake improved microvascular function when assessed as a group. Likewise, no significant differences were observed in blood pressure, plasma lipids, or platelet reactivity. Total fasting plasma nitrate/nitrite was not significantly changed with strawberry powder compared to control powder after one week of intake.

However, a significant increase in total plasma nitrate/nitrite levels was observed one hour after the intake of strawberry powder compared to the control.

Based on the results of the acute intake, and because strawberries are a source of dietary nitrate with a half-life of five to eight hours, a subset analysis was conducted. The researchers compared those who had an increase in the one week change in total plasma nitrate/nitrite after consuming the strawberry powder (“Responders”) with those who did not (“Non-Responders”). “Responders” did in fact have an increase in both RHI and fRHI, while “Non-Responders” had no improvement in vascular function.

Conclusion

The researchers conclude that “the literature to date strongly supports the concept that the regular consumption of strawberries can be associated with improvements in cardiovascular health.” However, there are limited long-term studies on strawberries’ impact on vascular function, especially in at-risk populations. More studies are needed in a variety of populations since hormonal status, sex, age, genetics, and microbial metabolism can affect polyphenol metabolism and ultimately cardiometabolic response. This study on adolescent males along with future research will better inform dietary recommendations about the amount and frequency of strawberry intake to support vascular health at varying life stages.

Source: Holt, R.R., Zuelch, M.L, Charoenwoodhipong, P., Al-Dashti, Y.A., Hackman R.M., et al. (2020). Effects of short-term consumption of strawberry powder on select parameters of vascular health in adolescent males. Food & Function, 11, 32-44. Doi: 10.1039/C9FO01844A

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