Does increased nitrate ingestion elevate nitrate levels in human milk?

To determine whether the nitrate content of human milk is influenced by maternal ingestion of water containing elevated nitrate levels.

Prospective, nonrandomized, volunteer study.

Clinical Research Center at the University of Iowa Hospitals and Clinics, Iowa City.

Twenty healthy lactating women with infants older than 6 months.

The mothers were asked to consume a minimum of 1500 mL of water containing 0 mg of nitrate per liter on day 1, 45 mg on day 2, and 100 mg on day 3 in addition to consuming and recording their dietary intake. Breast-feeding was permitted during days 1 and 2, but milk was expressed on day 3 and the infants were given alternate food sources. After each 24-hour study day, maternal urine and milk samples were collected and frozen. A modified cadmium column reduction method was used to determine spot urinary and milk nitrate content.

The meant total nitrate intake from diet and water on days 1,2, and 3, respectively, was 46.6, 168.1, and 272.0 mg. Spot urine nitrate content on days 1, 2, and 3, respectively, was 36.0, 66.0, and 84.0 mg. Nitrate concentration of human milk on days 1,2, and 3, respectively, was 4.4, 5.1 and 5.2 mg/L.

Women who consume water with a nitrate concentration of 100 mg/L or less do not produce milk with elevated nitrate levels.