Introduction and aims: Numerous studies have demonstrated that dietary nitrate supplementation increases nitric oxide (NO) bioavailability and reduces blood pressure (BP).  Individual differences in the response to nitrate ingestion have been suggested, with some researchers hypothesising the existence of nitrate ‘responders’ and ‘non-responders’.  However, the detection of interindividual differences in response to nutritional interventions is challenging and necessitates the use of specific methodological and statistical approaches. This presentation aims to provide a practical example of one approach for exploring interindividual differences in response to nutritional interventions, drawing upon a recently completed replicate crossover study on dietary nitrate.

Methods: Fifteen healthy males took part in a randomised double-blind placebo-controlled replicate crossover trial (Trial registration: https://clinicaltrials.gov/study/NCT05514821). They visited the laboratory on four occasions. On two visits, participants consumed 140 ml nitrate-rich beetroot juice (~14.0 mmol nitrate) and, on the other two visits, they consumed 140 ml nitrate-depleted beetroot juice as a placebo (~0.03 mmol nitrate). Plasma nitrate and nitrite were measured 2.5 hours post-supplementation. BP was measured pre- and 2.5 hours post-supplementation. We quantified individual response stability using placebo-adjusted between-replicate correlations and explored treatment response variability using within-participant linear mixed models and a novel meta-analytic approach.

Results: Nitrate-rich beetroot juice supplementation elevated plasma nitrate and nitrite concentrations and reduced systolic (mean:-7mmHg, 95%CI: -3 to -11mmHg) and diastolic (mean:-6mmHg, 95%CI: -2 to -9mmHg) BP versus placebo. The mixed model and meta-analytic approaches provided evidence of interindividual differences in response to nitrate supplementation. For example, for systolic BP the participant-by-condition interaction response variability from the mixed model was ±7mmHg (95%CI: 3 to 9mmHg), which was consistent with the treatment effect heterogeneity t=± 7mmHg (95%CI: 5 to 12mmHg) derived from the meta-analytic approach. The between-replicate correlations were moderate-to-large for plasma nitrate, nitrite and systolic BP (r=0.55 to 0.91), indicating good response stability for these variables.

Conclusions: These data suggest that the effects of dietary nitrate supplementation on NO biomarkers and systolic BP vary significantly from participant to participant. This provides proof-of-concept as a basis for further investigations of the magnitude, durability and pervasiveness of these interindividal response differences across diverse populations. This methodological approach could be applied to investigate interindividual differences in response to other nutritional or lifestyle interventions.