Children Living in Homes With High NO₂ Levels Have Shorter Sleep Duration

Children exposed to higher indoor nitrogen dioxide (NO₂) levels are more likely to have short sleep duration, according to results of a study published in Sleep.

Exposure to NO₂ has been related to all-cause mortality and cardio-respiratory outcomes, but it remains unclear whether it can affect sleep quality. The Environmental Assessment of Sleep Youth study recruited children (N=242) aged 6 to 12 years in the Boston area of the United States who were participating in the School Inner-City Asthma Study. The researchers assessed the physical environment of the participants’ homes, collected dust samples, and installed an Environmental Multipollutant Monitoring Assembly monitor.

The primary outcomes of this study were short sleep duration and sleep disordered breathing over a 7-night evaluation period. Short sleep duration was defined as an average duration of less than 8 hours, and sleep disordered breathing was defined as 5 or more Oxygen Desaturation Index events per hour, assessed by wrist-worn actigraphy and a home sleep monitor, respectively.

While indoor environmental exposures have long been implicated in asthma and respiratory tract infections, this novel finding suggests that elevated level of indoor NO₂ also may adversely affect children sleep health.

The children who did (n=178) and did not (n=60) live in a home with a gas cooking stove were aged mean (SD) 9.6 (1.9) and 9.4 (1.9) years, 45% and 38% were girls, 39% and 40% were Hispanic, and 31% and 37% were obese.

The children lived in areas with a mean (SD) Child Opportunity Index of 37.6 (30.1) and 27.4 (28.6), respectively. While gas stove use was more common in higher-income, more advantaged households, elevated indoor NO₂ exposure was more frequently observed in less advantaged households. The median of the average daily 95^th percentile NO₂ level in all participants’ homes was 41.1 (IQR, 38.4) ppb compared with an outdoor level of 10.3 (IQR, 4.5) ppb.

All included children had a mean (SD) sleep duration of 7.6 (0.9) hours, with 63% categorized as having short sleep, and 27% meeting criteria for sleep disordered breathing.

In the unadjusted models, living in a home with a gas cooking stove was not associated with short sleep duration (odds ratio [OR], 1.27; 95% CI, 0.70-2.31; P =.433) or sleep disordered breathing (OR, 0.74; 95% CI, 0.38-1.42; P =.361).

However, stratified by the level of exposure to NO₂, the children living in homes in at least the 80^th percentile of NO₂ levels were more likely to have short sleep duration (OR, 2.39; 95% CI, 1.15-4.99; P =.020) but not sleep disordered breathing (OR, 1.21; 95% CI, 0.62-2.35; P =.580). After adjusting for all potential confounders, including outdoor NO₂ levels, indoor small particulate matter (PM_2.5), and use of gas cooking, the highest exposure to indoor NO₂ remained associated with short sleep duration (OR, 2.84; 95% CI, 1.30-6.22; P =.009).

Study limitations include the possibility of residual confounding from additional sources of poor air quality, the focus on a single geographic region, and potential measurement misclassification.

The study authors concluded, “An elevated level of indoor NO₂ was common in an urban, predominantly low-income sample, and was associated with an increased odds of short sleep duration in children, even after accounting for multiple potential confounders. While indoor environmental exposures have long been implicated in asthma and respiratory tract infections, this novel finding suggests that elevated level of indoor NO₂ also may adversely affect children sleep health.”