Urban Noise Increases Risk of Alzheimers

Study finds that long-term exposure is linked to dementia

Quiet Street
A quiet street in Toronto.

Lloyd Alter

With the pandemic raging, many cities around the world have introduced "quiet streets" to reduce traffic and make safe routes for pedestrians and cyclists. However, there may be other benefits and other reasons to make them permanent; a recent study has found a correlation between long-term exposure to community noise and Alzheimer’s disease (AD) and mild cognitive impairment (MCI).

Urban noise has long been known to cause health issues; my colleague Starre Vartan quoted a study which found that living near airports "caused blood pressure spikes, increased pulse rates and set off vasoconstriction and the release of stress hormones. Worse, these harmful cardiovascular responses continued to affect individuals for many hours after they had awakened and gone on with their days." Now we are learning that the effects last a lifetime.

The new study was of particular interest to this Treehugger because we have often talked about the absence of noise being a big benefit in super-efficient buildings; it just doesn't get through the thicker walls and better windows. So can we now make a case that, say, living in a Passive House can help delay AD and MCI?

The study examined residents living on the South Side of Chicago who became part of the Chicago Health and Aging Project (CHAP), and used cognitive assessments going back to 1999. They determined sound exposure levels gathered in 2006 and 2007 and more recent data, and claim that they can calculate the noise level for a location within 3dBA.

"With this model, we first predicted noise levels at each participant's residential address using geographic covariates. ... We predicted residential noise levels for 7909 participants, of whom 5227 had complete data on outcomes and covariates. This resulted in 11,928 cognitive assessments for our analysis. Estimated levels of noise in the study area varied considerably with participant‐specific levels ranging from 51.1 to 78.2 dBA, with a mean of 56.2 dBA."
decibel scale

CDC

That's quite the range; the decibel scale is logarithmic, with every 10 dB meaning a doubling of noise.

"After adjustment for potential sources of confounding, community noise was associated with higher odds of both prevalent MCI and AD. Specifically, a 10‐dBA increment in noise exposure corresponded to a 36% higher odds of MCI and a 29% higher odds of AD."

That is a really significant increase. There are, however, some concerns; rich people live in quieter neighborhoods and poor people often live closer together near highways and noisier parts of town, subject to all kinds of pollution besides just noise, although in the discussion, the authors say they took this into account.

In this first U.S.‐based study of its kind, higher long‐term exposure to community noise was associated with higher odds of MCI and AD as well as worse cognitive performance—specifically, perceptual speed—in older adults. These associations were observed across a range of noise levels that are typical in the United States, ranging from a quiet suburb to noisier urban settings near large automotive expressways. These associations were also independent of several measures of socioeconomic status and exposure to traffic‐related air pollution, which was only weakly associated with noise exposure.

I must note that the researchers didn't actually do noise tests inside anyone's apartment or home, which could make a dramatic difference in noise levels, depending on the quality of construction or whether one was even facing the street or not. A calculated noise level outside a building in the daytime could have very little relationship to what actually is happening inside where the person lives. Other critics of the paper note that there are many other factors in play with AD and MCI.

"Many of the risk factors that have been found to increase our risk of dementia as we age are heavily associated with social disadvantage – from education to obesity. We need policies to address all these across the life course to ensure healthy brains, in which good quality housing, environments and employment play a major part.”

But the study authors are pretty confident in their data:

In conclusion, higher long‐term exposure to community noise was associated with higher prevalence of MCI and AD and worse cognitive performance, especially perceptual speed. This association was detected in a diverse, urban, U.S.‐based population of older adults with noise exposures that are likely to be consistent with exposure levels in other U.S. metropolitan areas. Therefore, if noise exposure does contribute to dementia risk—a question that warrants continued investigation, particularly in U.S. settings—its abatement may be a means for reducing the population burden of dementia.
Noise Reduction in Passive House

NK Architects

The study does provide another good reason to go for seriously efficient housing, such as Passive House; a study by NK Architects found that it reduced noise levels by 10 dB*, making it fully 50% quieter. As noted earlier, the study found that a 10‐dBA* increment in noise exposure corresponded to a 36% higher odds of MCI and a 29% higher odds of AD.

As the study authors concluded, noise abatement "may be a means for reducing the population burden of dementia." Another good reason to keep quiet streets in place long after the pandemic recedes, and to build better, quieter buildings to keep the noise out.

*dB is directly related to sound pressure; dBA have been adjusted to take into account how the human ear is sensitive to different frequencies. According to consultant SoftdB, "Compared with dB, A-weighted measurements underestimate the perceived loudness, annoyance factor, and stress-inducing capability of noises with low-frequency components, especially at moderate and high volumes of noise."