Objective: This study aims to investigate the effects of milk on a measurement of exhaled carbon monoxide
(CO).
Methods: Eleven healthy non-smokers (aged 21– 59) were recruited. After an overnight fast, exhaled CO of the subjects was measured using three different portable CO monitors (A, B, and C). After taking 400 ml-milk containing lactose at 9:00 am, exhaled CO of the subjects was measured every 30 min for about eight hours.
Results: The median values (25 percentile, 75 percentile) before taking milk were A: 1.0 (1.0, 3.0) ppm, B: 2.0 (1.0, 2.0) ppm, C: 1.0 (1.0, 1.5) ppm, respectively. After taking milk, CO values using every monitor were significantly increased; A: 6.0 (4.5, 10.0) ppm, B: 11.0 (7.0, 16.0) ppm, C: 3.0 (2.5, 3.5) ppm (A: p = 0.003, B: p = 0.003, C: p = 0.003).
Conclusions: Non-smokers’ CO values as measured by a CO monitor increased after taking milk including lactose. The effects of taking milk should be considered before measuring CO with a portable CO monitor.