Hydroponic vs Conventional Spinach Smoothies: Effects on Salivary Nitrate Bioavailability and Blood Pressure

Official title

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

Overview

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).

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.

Interventions

• 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.

Primary outcome measures

• Salivary nitrate concentration [Time frame: Baseline and 2 hours post-consumption]

Secondary outcome measures (4)

• Systolic blood pressure [Time frame: Baseline and 2 hours post-consumption]
• Diastolic blood pressure [Time frame: Baseline and 2 hours post-consumption]
• Mean arterial pressure [Time frame: Baseline and 2 hours post-consumption]
• Heart rate [Time frame: Baseline and 2 hours post-consumption]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Crossover

Masking

Triple blind

Primary purpose

Treatment

Study locations

United Kingdom · 1 center

• University of Plymouth — Plymouth

Publications

• Qadir OK, Seal CJ, Ashor AW, Tassotti M, Mena P, Del Rio D, Siervo M, Brandt K. Double-blind controlled dietary cross-over intervention with differentially fertilised intact lettuce leaves shows acute reduction in blood pressure in young adults, associated with faster uptake of nitrate than of phenolics. Eur J Nutr. 2022 Dec;61(8):4191-4203. doi: 10.1007/s00394-022-02961-5. Epub 2022 Jul 23. PMID 35871120
• Jackson JK, Patterson AJ, MacDonald-Wicks LK, Oldmeadow C, McEvoy MA. The role of inorganic nitrate and nitrite in cardiovascular disease risk factors: a systematic review and meta-analysis of human evidence. Nutr Rev. 2018 May 1;76(5):348-371. doi: 10.1093/nutrit/nuy005. PMID 29506204
• Hosseini MJ, Dezhangah S, Esmi F, S Gharavi-Nakhjavani M, Hashempour-Baltork F, Mirza Alizadeh A. A worldwide systematic review, meta-analysis and meta-regression of nitrate and nitrite in vegetables and fruits. Ecotoxicol Environ Saf. 2023 Jun 1;257:114934. doi: 10.1016/j.ecoenv.2023.114934. Epub 2023 Apr 19. PMID 37084661
• Bryan NS, Ahmed S, Lefer DJ, Hord N, von Schwarz ER. Dietary nitrate biochemistry and physiology. An update on clinical benefits and mechanisms of action. Nitric Oxide. 2023 Mar 1;132:1-7. doi: 10.1016/j.niox.2023.01.003. Epub 2023 Jan 20. PMID 36690137
• Blekkenhorst LC, Bondonno NP, Liu AH, Ward NC, Prince RL, Lewis JR, Devine A, Croft KD, Hodgson JM, Bondonno CP. Nitrate, the oral microbiome, and cardiovascular health: a systematic literature review of human and animal studies. Am J Clin Nutr. 2018 Apr 1;107(4):504-522. doi: 10.1093/ajcn/nqx046. PMID 29635489
• Bian Z, Wang Y, Zhang X, Li T, Grundy S, Yang Q, Cheng R. A Review of Environment Effects on Nitrate Accumulation in Leafy Vegetables Grown in Controlled Environments. Foods. 2020 Jun 3;9(6):732. doi: 10.3390/foods9060732. PMID 32503134

Identifiers

NCT: NCT07665944 · 6910

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗