The roar of a jet plane, the rumble of a big rig, that shrill scream from the siren of a speeding emergency vehicle: The common but loud noises that keep you awake at night and agitate you throughout the day may have a notable effect on your cardiovascular health, experts say.
Researchers say noise pollution may raise the risk of heart disease, such as coronary artery disease, hypertension and heart failure, according to a review paper published last week in the Journal Of The American College Of Cardiology.
The authors, who examined research on noise pollution and heart disease, say loud sounds not only disrupt sleep, which can lead to health problems, but can also ignite the stress response, releasing a rush of hormones that, over time, can damage the heart.
"Ten years ago, people were saying that noise is just annoying, but now I think there's considerable evidence that noise makes you sick, and one of the predominate diseases is cardiovascular disease," lead author Thomas Munzel said last Tuesday in a phone interview with The Washington Post.
The research does not prove that loud noises cause heart disease. But Dr Munzel of the cardiology centre at University Medical Centre, Johannes Gutenberg University Mainz, in Germany, told ABC News that noise pollution - or unwanted environmental noise - is a risk factor for heart disease in the same way that high cholesterol and obesity may increase the odds.
Those confronted with noise pollution, which causes disturbances to communication during the day and sleep at night, may have higher stress hormone levels, he said.
Over time, Dr Munzel said, it can take a toll on the body - increasing cholesterol, blood pressure and heart rate.
Ten years ago, people were saying that noise is just annoying, but now I think there's considerable evidence that noise makes you sick, and one of the predominate diseases is cardiovascular disease.
LEAD AUTHOR THOMAS MUNZEL
"If this persists for years, then you have a risk of coronary artery disease, stroke, heart failure and arrhythmia," he told The Post.
He also said long-term noise pollution may be linked to depression and anxiety disorders as well as problems with cognitive development in young children.
But in researching the link between noise pollution and heart disease, experts warn that there are also factors that can complicate the findings. For instance, people who live in heavily populated areas more likely to be plagued by noise are also exposed to more particle pollution in the air, which can also cause heart problems.
Also, people who live in such areas may have a different socio-economic status, meaning they may not have the same access to healthcare or healthy foods.
Still, Professor Steve Kopecky, a specialist in cardiovascular diseases at the Mayo Clinic, said noise and how it affects health is something to consider.
"I think it's something we need to pay more attention to in terms of our everyday living," he said.
The World Health Organisation (WHO) calls noise pollution "an underestimated threat" that can cause "sleep disturbance, cardiovascular effects, poorer work and school performance, hearing impairment".
It has published guidelines for community noise, recommending 30 A-weighted decibels in the bedroom for a good night's sleep.
A car measures 70 decibels, a jackhammer 100 decibels and an airplane takeoff 120 decibels, according to a WHO decibel scale cited by ABC News.
"Though there is no set threshold to establish risk, we do know that anything above 60 decibels can increase risk for heart disease," Dr Munzel told the station.
"We need more research to determine what duration of exposure to loud noise is harmful, but we do know the risk comes from years and years of exposure, not days."
Experts say loud noises, especially when people are not expecting them, can trigger the stress response.
HOW DOES IT WORK? According to the Mayo Clinic, when a person senses a threat, "your hypothalamus, a tiny region at the base of your brain, sets off an alarm system in your body".
It states: "Through a combination of nerve and hormonal signals, this system prompts your adrenal glands, located atop your kidneys, to release a surge of hormones, including adrenaline and cortisol.
"Cortisol curbs functions that would be non-essential or detrimental in a fight-or-flight situation. It alters immune system responses and suppresses the digestive system, reproductive system and growth processes. This complex natural alarm system also communicates with regions of your brain that control mood, motivation and fear."
Prof Kopecky said people may not pay attention to certain sounds when they expect them - like hearing car horns while in bumper-to-bumper traffic - but that same sound when it's unexpected - like when a person is asleep - can trigger the stress response.
He said there are several ways that response can lead to damage: The rush of hormones causes the arteries to constrict, which can damage the lining of the arteries and lead to heart disease. It can also raise blood pressure or make the blood more likely to clot, which is a problem with heart attacks.
But regardless of where a person lives, Prof Kopecky said, there are things that can be done, especially when it comes to sleep, such as using a white noise machine to help drown out unwanted sounds.
THE WASHINGTON POST