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

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^-].