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-].