Nitrate and Nitrite Concentrations in Fingertip Serum Following Beetroot Juice Ingestion Correlate with Those in Venous Plasma

Abstract

Dietary nitrate (NO₃⁻) supplementation can offer health benefit and improve exercise performance by increasing nitric oxide (NO) through NO₃⁻-nitrite (NO₂⁻)-NO pathway. Individuals may benefit from dietary NO₃⁻ supplementation by monitoring blood [NO₃⁻] and [NO₂⁻], although a simple and practical method for assessing blood [NO₃⁻] and [NO₂⁻] has not been established. We examined whether fingertip serum samples could substitute for venous plasma samples in assessing [NO₃⁻] and [NO₂⁻]. Ten young adults consumed 140 mL of nitrate-rich beetroot juice. Fingertip serum and venous plasma samples were collected at baseline and every hour for up to 4 h after ingestion. [NO₃⁻] and [NO₂⁻] were similar between samples at baseline, whereas they were higher in fingertip serum throughout the post-ingestion periods. Significant correlations existed between fingertip serum vs. venous plasma for both [NO₃⁻] and [NO₂⁻] throughout post-drink periods, except [NO₃⁻] assessed at 2 and 4 h after ingestion of beetroot juice. We show that although fingertip serum [NO₃⁻] and [NO₂⁻] overestimate those measured by venous plasma after dietary NO₃⁻ intake (125–141% and 156–183% of venous values), [NO₃⁻] and [NO₂⁻] in fingertip serum samples may be utilized for assessing blood [NO₃⁻] and [NO₂⁻] levels, although [NO₃⁻] assessment may lack precision compared to [NO₂⁻].