Time-dependent effect of nitrate-rich meals on exhaled nitric oxide in healthy subjects

Exhaled nitric oxide (eNO) is a convenient noninvasive marker for airway inflammation in several pulmonary diseases. However, external factors such as nitrate-rich nutrition can affect the levels of eNO and thus compromise its diagnostic value.

The objective of this investigation was to have a better understanding of the time-dependent effect of nitrate-rich meals on eNO in healthy subjects.

Forty-two healthy, nonsmoking volunteers (age range, 25 to 62 years) were recruited for the study. They had no recent respiratory tract infections and were free of pulmonary history, rhinitis, and atopic disorders. eNO was measured before, and 0.5, 2, 4, 12, 15, and 20 h after the intake of a nitrate-rich meal equivalent to 230 mg of nitrate.

The intake of a nitrate-rich meal increased eNO by 60% 2 h after the meal. Even after 15 h, the mean eNO value was still 22% higher than the baseline value. Only after 20 h did eNO return to the normal baseline level.

This finding stresses the importance of advising patients to avoid nitrate-rich nutrition at least 20 h before a scheduled measurement of eNO.