The short version
- A single night of simulated road traffic at 41 to 44 dB, quieter than the WHO’s night-time guideline, measurably reduced blood-vessel flexibility in healthy adults.
- The study was a randomized, double-blind crossover in people’s own bedrooms, so each participant served as their own control.
- The effects were acute and measured the next morning; the link to long-term heart disease still has to be made.
One night of road noise quiet enough to pass the World Health Organization’s night-time guideline was enough to stiffen the blood vessels of healthy adults by the next morning, in a study published in Cardiovascular Research by a team at University Medical Center Mainz.
The design
The researchers, O. Hahad, T. Münzel, A. Daiber and colleagues, recruited 74 healthy adults and ran the experiment where noise actually happens: in each participant’s own bedroom. Each person slept through three conditions in random order, and neither they nor the staff assessing them knew which night was which.
- Silence: an average level of 30.7 dB, roughly a quiet rural night.
- 30 traffic events: average 41.4 dB.
- 60 traffic events: average 44.1 dB, with peaks around 60 dB, about the level of a normal conversation.
Each “event” was a recorded vehicle pass-by lasting 75 seconds, played every 9.5 to 11.5 minutes, so the 60-event night meant a car or truck going past about every 10 minutes from lights-out to morning.
For scale: the WHO’s night-noise guideline for Europe sets a threshold above these averages. These were, by the standard most cities use, acceptable nights.
The results
Heart rate rose after each noise event. In the morning, flow-mediated dilation, a standard ultrasound measure of how well an artery in the arm widens in response to blood flow and a marker of vascular health, was lower after the noise nights than after the quiet one. Participants also rated their sleep as worse.
The team went a step further and ran proteomics, a scan of blood proteins. In the participants whose vessels reacted worst, they saw changes in interleukin signalling and chemotaxis, the pathways the immune system uses to call inflammatory cells to a site. The vascular effect, in other words, came with an inflammatory signature.
Münzel’s summary line: “Noise protection is heart protection.”
The limits
This is one night, and the measurements are acute. Flow-mediated dilation recovers; a stiff artery on Tuesday morning is not a heart attack. The large epidemiological studies linking chronic traffic noise to cardiovascular disease are observational, and this experiment supplies a mechanism for them rather than a direct link. The step from “one night does this” to “ten years of nights do that” still has to be taken.
Participants were healthy adults. The people most likely to live beside busy roads, older people, shift workers and those who already have cardiovascular disease, were not the sample.
And 74 people, each measured three times, is a solid crossover but not a large trial. The proteomics finding in particular comes from a subgroup of the worst responders and should be read as a lead.
Why it matters
The study matters less for the size of the effect than for where the effect appeared: below the thresholds regulators call safe, in a dose a great many people get every night, on a night the participants themselves did not describe as unusually bad.
It also lines up with a different study from the University of Surrey this summer, which found that traffic noise at levels below WHO limits erased the measurable wellbeing benefit of birdsong and lowered heart-rate variability in a lab group of 63 people. Two labs, two outcomes, the same quiet traffic.
The practical implication is modest and cheap. A closed window, earplugs, or a bedroom on the far side of the house from the road are all ways of turning a 44 dB night back into a 31 dB one. A sound machine is a different bet: it adds sound rather than removing it, and a 2026 Penn study found pink noise played all night shortened REM sleep, so masking is not the same as quiet.
What to watch
Whether the Mainz group follows the same participants over repeated noise nights, and whether the inflammatory signature in the blood holds up in a bigger sample. The question that would change policy is whether the acute effect accumulates. This study makes that question harder to ignore.
