Sleep disturbance is increasingly recognized as being important to public health; it is known to be associated with elevated risks of coronary heart disease, type 2 diabetes, and depression. Safety issues such as motor vehicle crashes, industrial disasters, and errors in medicine and other occupations are also consequences of sleep disturbance.
The effects of occupational and recreational/ leisure time noises on hearing are well established. Studies have also reported non-auditory adverse health effects, including ischemic heart disease, stroke, hypertension, and metabolic syndrome. Moreover, environmental noise during the day can cause annoyance, traffic noise at night leads to lower cognitive performance and annoyance, and other noises at night can provoke sleep disturbance.
However, in many modern cities, considerably more frequent exposure to loud environmental noise has been observed during the day than at night. Some people took the amount of day/night environment noise for granted. It is not well known that environmental noise exposure in the day will or will not cause adverse health effects and sleep quality.
A group of researchers from Taiwan recruited 40 workers in hospital cafeterias and studied their sleep after one day in high noise-exposed areas and after another day in quieter areas. They collected data and analyzed with parameters that included blood pressure, sympathetic tones, stress-hormone cortisol, and sleep quality.
This study revealed that high noise conditions had average noise levels ranging from 71.1 to 85.8 decibels (dBA), while low noise conditions ranged from 66.9 to 72.8 dBA. These daytime noise levels commonly encountered in modern life caused higher blood pressure, higher sympathetic tones, and higher levels of cortisol after work. The sustained effect also induced poor sleep quality at night, such as shorter deep sleep and worse sleep efficiency.
The research team found that occupational noise significantly affected deep sleep. Compared with personal noise exposure of 55 dBA, exposure of 70 dBA reduced deep sleep by 19.3%. Despite the WHO guidelines recommending a daytime noise exposure of 55 dBA or less in residential areas, noise levels in large cities frequently exceed this level. For example, surveys have reported a noise level of 70 dBA or greater during 13%, 28%, 50%, 60%, and 81% of the day in Dublin (Ireland), Barcelona (Spain), New York (USA), Ca’ceres (Spain), and Curitiba (Brazil), respectively.
Sleep is an important and complex physiological process that is critical in order for humans to maintain metabolic homeostasis. Disturbances in metabolic homeostasis can increase the risk for diabetes, obesity, and heart disease; therefore, our findings of reduced deep sleep caused by daily noise implies important cardio-metabolic risks, particularly in people residing in modern cities.
This study suggested being exposed to a noisy (but not very noisy) workplace all day might induce stress that can carry into the evening and impact sleep quality. Furthermore, these daily noise exposure levels quite frequently encountered in modern cities affected sleep quality, probably through autonomic mechanisms. The risks of poorer sleep quality and associated metabolic disturbances induced by daily noise exposure warrant further investigation.
These findings are described in the article entitled Will daytime occupational noise exposures induce nighttime sleep disturbance?, recently published in the journal Sleep Medicine. This work was conducted by Cheng-Yu Lin from the National Cheng Kung University Hospital and Tainan Hospital, Ministry of Health and Welfare, Perng-Jy Tsai and Jiunn-Liang Wu from the National Cheng Kung University and National Cheng Kung University Hospital, Kuei-Yi Lin from the National Chung-Shan Institute of Science & Technology, Chih-Yong Chen and Lin-Hui Chung from the Institute of Labor, Occupational Safety and Health, Ministry of Labor, Executive Yuan, and Yueliang Leon Guo from the National Taiwan University and National Taiwan University Hospital and the National Institute of Environmental Health Science, National Health Research Institutes, Taiwan.