Rise and Shine: How Noise Pollution Hijacks Your Sleep

Triple Helix
4 hours ago
4 min read

Written by: Nhi Nguyen ‘28

Edited by: Kevin Pham ‘28

It’s 5 a.m.

The sun has barely crested the horizon, yet the hum of traffic—a trash truck rumbling by, motorcycles at untimely hours, wails of an ambulance—still leaks through the closed windows. You stir in your bed, unwilling to wake up. Nevertheless, the slight noise disturbance has already roused the brain from its stages of deep sleep. What should have been a restorative night’s rest has instead triggered a cascade of metabolic reactions, setting off the body’s stress response.

Sleep is a fundamental aspect of life—so much so that the average person spends nearly one-third of their life asleep (2). During quality sleep, the body rests, but the brain is still bustling with activity. Networks of neurons begin producing rhythmic waves that drive the flow of cerebrospinal fluid through the dense brain tissues (3). This mechanism of the glymphatic system flushes away metabolic waste and protein debris that, if left to accumulate, could result in neurodegenerative diseases (3). Sleep also modulates hormonal release (4). Growth hormones are secreted, aiding in lipolysis (breaking down stored fat for energy) and muscle growth (5). At the same time, sleep suppresses cortisol (a stress hormone) and the hypothalamic-pituitary-adrenal (HPA) axis to inhibit and regulate stress responses (5). Simultaneously, the brain also forms new synaptic connections and remodels existing ones, strengthening the memory system (6). In these ways, restorative sleep facilitates healthy brain functioning.

Nocturnal noise pollution can readily disrupt this cycle, with sound levels as low as 48 dB—roughly the sound of light traffic or rain—capable of perturbing the sympathoadrenal (sympathetic and adrenal) and endocrine systems (4,7,8). The noise stimulus activates the brain's limbic region, eliciting an emotional response that signals the hypothalamus to release corticotropin-releasing hormone (CRH) (7). CHR is crucial in regulating the body’s response to stress, as it stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream (7). ACTH, in turn, induces the adrenal glands to produce glucocorticoid hormones, one of which is cortisol (7). The diurnal rhythm of cortisol, regulated by the HPA axis, is responsible for the body’s circadian rhythm (9). Cortisol levels normally peak during the transition from sleep to wakefulness, and gradually decrease during the evening (9). However, if cortisol levels rise while the brain is still in sleep, processes such as memory consolidation can be disrupted, and the glymphatic system may be impaired (10,11).

The fragmented sleep cycle results in shallower sleep that can increase the risk for cardiovascular diseases (4,7). The circulating stress hormones can disrupt endothelial function, reducing the system’s ability to dilate blood vessels (7). This is a hallmark predictor for atherosclerosis, where plaque builds up and triggers blood clot formation (7). During noise stimulation, the sympathetic system also increases heart rate and blood pressure (7). Chronic noise pollution resulting in prolonged blood flow through constricted vessels can lead to adverse health effects such as ischemic heart disease, arterial hypertension, stroke, and myocardial infarction (heart attack) (7).

After the noise disturbance, you roll onto your side and drift back to sleep, blissfully unaware that your brain is already awake and preparing for the day. Despite getting eight hours, episodes of daytime sleepiness and fatigue may still occur as a result of environmental noise (4). These effects often go unnoticed, allowing symptoms to accumulate gradually over the years. Such symptoms undergo the same pathophysiological pathways as cerebrovascular risk factors, such as obesity, diabetes, and hypertension (7). As such, the long-term consequences of nocturnal noise disturbances can compound into conditions later in life. This underscores the importance of noise ordinances within residential areas of urban neighborhoods, especially in low-income communities where noise levels are disproportionately higher (12). Nevertheless, auditory stress is rarely considered in community policymaking, and the recommended efforts taken are not proactive enough to induce widespread changes (13). This is mainly because decision makers lack sufficient information, since research dedicated to noise pollution and population health is minimal (12,13). As more and more people migrate to urban areas, there is an increased need for research that can incite preemptive policies dedicated to improving noise pollution and ultimately, sleep.