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

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.

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