# Total Nitrite and Nitrate Concentration in Human Milk and Saliva during the First 60 Days Postpartum—A Pilot Study

## TL;DR

This pilot study measured nitrite and nitrate levels in human milk and saliva during the first 60 days postpartum and found higher levels in the early period.

## Contribution

The study is the first to longitudinally assess NOx concentrations in human milk and saliva during early postpartum.

## Key findings

- NOx concentration in milk was significantly higher during the first 30 days compared to day 60.
- Milk and saliva NOx concentrations were positively associated throughout the study period.
- Partially breastfeeding mothers had lower NOx levels in milk on day 2 compared to exclusively breastfeeding mothers.

## Abstract

Nitric oxide (NO) in human milk may have important functions in lactation and infant health. This longitudinal pilot cohort study investigated the total nitrite and nitrate (NOx) concentration in human milk and maternal saliva during the first 60 days postpartum. Additionally, we explored the association between selected breastfeeding variables and milk and saliva NOx concentration. Human milk and maternal saliva samples were collected on days 2, 5, 14, 30, and 60 postpartum and analyzed for NOx concentration. Breastfeeding data were collected through self-assessed questions. Data analyses were performed using mixed models. The concentration of NOx in milk was significantly higher during the first 30 days compared to day 60, and there was a positive association between milk and saliva NOx concentrations throughout the entire study period. In absolute numbers, partially breastfeeding mothers had a lower concentration of NOx in milk on day 2 compared to exclusively breastfeeding mothers (8 vs. 15.1 μM, respectively). Partially breastfeeding mothers reported a later start of secretory activation and fewer mothers in this group started breastfeeding within the first hour after birth. Due to the small numbers, these differences could not be statistically evaluated. Further research is warranted to elucidate the role of NO in lactation success and breastfeeding outcomes.