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.
The new findings, reported in the May issue of the journal Environmental Health Perspectives, 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,
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