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Even the minor noise that fills everyday life, from the ring of a cell phone to the conversation that follows, may have short-term effects on heart function, a small new study suggests.
In the study of 110 adults equipped with portable heart monitors, researchers found that people's heart rate tended to climb as their noise exposure increased - even when the noise remained below 65 decibels. That's about as loud as a normal conversation or laughter.
There was also a negative impact on people's heart rate "variability" - a measure of the heart's adaptation to what is going on around you. Greater variability in the interval between heartbeats is better. When people are relaxed, the space between heartbeats is usually a bit longer as they exhale, and shorter as they inhale.
When people are stressed, however, some of that natural variation is lost. And studies have linked lesser heart rate variability to an increased risk of heart attack.
So does all of this mean you need to wear earplugs to protect your heart?
Probably not, experts say.
Loud workplaces
For any one person, the effects of everyday noise on heart function may be small, said Charlotta Eriksson, a researcher at the Karolinska Institute, in Stockholm, Sweden. Eriksson was not involved in the study.
But since we are all exposed to noise, even a minor effect on heart health could be important on the broad "population level," said Eriksson, who has studied the effects of loud traffic - from roads or airports - on people's blood pressure and heart function.
Research has consistently found links between loud workplaces and an increased risk of heart disease, said Dr Wenqi Gan, a researcher at North Shore-LIJ Health System's Feinstein Institute for Medical Research, in Manhasset, NY.
The evidence is more mixed when it comes to "community noise," like traffic sounds, said Gan, whose own research has found a connection.
He said the mixed results may be because it's difficult to weed out the effects of community noise on individuals. You might live in a noisy section of a big city, but have good, sound-muffling windows, for example.
"And some people are more sensitive to noise than others," Gan said. If noise affects the heart by stressing people out, he said, then your personal sensitivity to it would be important.
Fight or flight mode
The new findings are based on 110 adults who wore portable devices that measured their heart activity and noise exposure during their normal daily routines.
What was "interesting," Eriksson said, is that lower-level noise seemed to curb activity in the parasympathetic nervous system - the branch of the nervous system that acts as a "brake," lowering heart rate and relaxing the blood vessels, for example.
Louder noise, meanwhile, seemed to rev up the sympathetic nervous system - the branch that boosts heart rate, constricts blood vessels and otherwise sends us into "fight or flight" mode.
The value of the findings is that they suggest a biological reason for why noise has been linked to ill heart effects, said Alexandra Schneider, one of the researchers in the Institute of Epidemiology at Helmholtz Zentrum Munchen, in Germany, who worked on the study.
"Our main focus was to find a possible mechanism that could be responsible for the observed health effects in other studies," Schneider said.
The study was not designed to offer people advice on how much noise is "bad" for their hearts, she said.
Gan agreed. "This study is a first step in exploring the underlying biological mechanisms for the association between noise exposure and cardiovascular disease," he said. "We need more studies like this."
A big question, said study author Schneider, is whether the short-term effects of noise, repeated over time, ultimately affect heart health - particularly for people who already have chronic medical conditions.
Although the study tied increased noise exposure to a rise in heart rate, it did not establish a cause-and-effect relationship.
More information
The US Environmental Protection Agency has more information on noise pollution.
