Hydroponic vs Conventional Spinach Smoothies: Effects on Salivary Nitrate Bioavailability and Blood Pressure (SPIN-BP-NO)

June 18, 2026 updated by: Raul Bescos, University of Plymouth

Acute Effects of Hydroponically vs. Conventionally Grown Spinach Smoothies on Salivary Nitrate Bioavailability and Blood Pressure: A Randomized Controlled Crossover Trial

The goal of this clinical trial is to determine whether hydroponic spinach (HS) versus conventional spinach (CS) smoothies produce differential post-consumption effects on salivary nitrate availability and blood pressure in adults.

The main questions it aims to answer are:

Do hydroponic spinach (HS) and conventional spinach (CS) smoothies produce differential post-consumption salivary nitrate availability responses in adults when consumed in equal volumes? Do hydroponic spinach (HS) and conventional spinach (CS) smoothies produce differential post-consumption blood pressure responses in adults when consumed in equal volumes?

Participants will:

Consume hydroponic spinach (HS) and conventional spinach (CS) smoothies on two separate study days.

Attend two laboratory visits at the university, scheduled within a 1-2 week period.

Undergo check-ups and study measurements during each visit (e.g., blood pressure and saliva sampling).

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

This randomized, double-blind, crossover study will investigate the acute effects of hydroponic spinach (HS) compared with conventional spinach (CS) smoothies on vascular responses in adults. The study aims to determine whether HS and CS smoothies elicit differential effects on nitrate bioavailability and blood pressure.

Spinach is a rich source of dietary nitrate, which can be converted via the enterosalivary pathway to nitrite and subsequently to nitric oxide, a key regulator of vascular function and blood pressure. The nitrate content of spinach varies according to cultivation methods, with hydroponically grown spinach often reported to have higher nitrate concentrations than conventionally grown spinach. However, it remains unclear whether these compositional differences translate into meaningful physiological effects following consumption.

Participants will attend two laboratory visits separated by a washout period of approximately 7-14 days. In this randomized crossover design, each participant will receive both interventions in a randomized order, enabling within-subject comparisons. At each visit, participants will consume a standardized smoothie containing either hydroponic or conventional spinach. The smoothies will be matched for volume and appearance to maintain blinding of both participants and investigators.

Baseline measurements will be obtained prior to smoothie consumption. Following intake, measurements will be repeated over the acute postprandial period, including at 2 hours post-consumption, to assess physiological responses. These assessments will include saliva samples to evaluate nitrate bioavailability (salivary nitrate) and cardiovascular measures-systolic blood pressure, diastolic blood pressure, mean arterial pressure (MAP), and heart rate (HR).

The crossover design allows each participant to act as their own control, thereby reducing inter-individual variability and improving statistical power in this pilot investigation.

Study Type

Interventional

Enrollment (Estimated)

12

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • United Kingdom
    • Devon
      • Plymouth, Devon, United Kingdom, PL4 6AB
        • Recruiting
        • University of Plymouth
        • Contact:
        • Contact:
        • Principal Investigator:
          • Raul Bescos, PhD
        • Principal Investigator:
          • Patricia Casas Agustench, PhD

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Adults aged 18-60 years
  • Generally healthy individuals (no diagnosed chronic disease)
  • Non-smokers and non-vapers
  • Not currently taking medications known to affect cardiovascular function or nitrate metabolism
  • Able and willing to provide informed consent
  • Willing to comply with study procedures and attend both study visits

Exclusion Criteria:

  • Presence of chronic disease (e.g., cardiovascular, metabolic, renal, or respiratory conditions)
  • Use of pacemakers or implanted medical devices
  • Pregnant or lactating individuals
  • Known allergy or intolerance to spinach
  • History of gastrointestinal disorders or pathology affecting digestion or absorption
  • Use of nitrate or nitrite supplements
  • Use of antibiotics within the past 3 weeks
  • Use of antibacterial mouthwash or oral products within the past 2 weeks
  • Current participation in another clinical trial or recent participation that may interfere with outcomes

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Hydroponic then Conventional Spinach
Participants consume a hydroponic spinach smoothie at the first visit followed by a conventional spinach smoothie at the second visit, separated by a washout period.
Other: Hydroponic spinach smoothie
Standardized smoothie prepared with hydroponically grown spinach, matched for volume and appearance.
Other: Conventional spinach smoothie
Standardized smoothie prepared with conventionally grown spinach, matched for volume and appearance.
Experimental: Conventional then Hydroponic Spinach
Participants consume a conventional spinach smoothie at the first visit followed by a hydroponic spinach smoothie at the second visit, separated by a washout period.
Other: Hydroponic spinach smoothie
Standardized smoothie prepared with hydroponically grown spinach, matched for volume and appearance.
Other: Conventional spinach smoothie
Standardized smoothie prepared with conventionally grown spinach, matched for volume and appearance.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Salivary nitrate concentration
Time Frame: Baseline and 2 hours post-consumption
Salivary nitrate levels assessed at baseline and 2 hours post-consumption as a marker of nitrate bioavailability.
Baseline and 2 hours post-consumption

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Systolic blood pressure
Time Frame: Baseline and 2 hours post-consumption
Systolic blood pressure measured at baseline and 2 hours after consumption of hydroponic and conventional spinach smoothies.
Baseline and 2 hours post-consumption
Diastolic blood pressure
Time Frame: Baseline and 2 hours post-consumption
Diastolic blood pressure measured at baseline and 2 hours after consumption of hydroponic and conventional spinach smoothies.
Baseline and 2 hours post-consumption
Mean arterial pressure
Time Frame: Baseline and 2 hours post-consumption
Mean arterial pressure measured at baseline and 2 hours post-consumption.
Baseline and 2 hours post-consumption
Heart rate
Time Frame: Baseline and 2 hours post-consumption
Heart rate measured at baseline and 2 hours post-consumption.
Baseline and 2 hours post-consumption

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Plymouth

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

May 22, 2026

Primary Completion (Estimated)

June 19, 2026

Study Completion (Estimated)

July 31, 2026

Study Registration Dates

First Submitted

June 10, 2026

First Submitted That Met QC Criteria

June 18, 2026

First Posted (Actual)

June 24, 2026

Study Record Updates

Last Update Posted (Actual)

June 24, 2026

Last Update Submitted That Met QC Criteria

June 18, 2026

Last Verified

June 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 6910 (CTEP)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

UNDECIDED

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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