Scientists warn against exposure to loud sounds after discovering link to devastating neurological disease

Being exposed to loud noises for just an hour a day could worsen signs of Parkinson's disease, a study suggests.

Researchers in China looked at mice that were modified to be in the early stages of Parkinson's disease, a progressive neurological disorder caused by the death of nerve cells in the brain that produce dopamine.

Suffered by about 1million Americans, the lack of dopamine leads to tremors, balance issues, stiffness and trouble speaking, all of which worsen over time.

In the experiment, mice had Parkinson's disease but were not yet showing symptoms.

Researchers exposed the mice to either short bursts or chronic amount of loud noises measuring between 85 and 100 decibels, about as loud as a lawn mower or blender.

After just one hour of being around the noise, the mice began to move more slowly and had reduced balance compared to those in the control group.

While they recovered one day later, mice who were exposed to the noise for an hour per day for a week showed chronic movement difficulties.

Additionally, the team found the brain's inferior colliculus, which processes sound, is connected to the substantia nigra pars compacta, a dopamine-producing area that becomes severely damaged in Parkinson's.

Chronically activating the inferior colliculus, they noted, mimicked the effects of loud noises in mice with Parkinson's by killing cells that produce dopamine.

The study authors wrote that the findings highlight 'potential role of environmental factors in exacerbating Parkinson's Disease pathogenesis.'

The Parkinson's Foundation estimates 1.2million Americans will be diagnosed with Parkinson's by 2030, and 90,000 are struck by the disease every year. There are roughly 35,000 deaths annually.

This is a 50 percent increase from the previously estimated rate of 60,000 a decade ago, the foundation estimates.

Experts believe environmental factors could partly be to blame for the rise of Parkinson's disease in the US.

Researchers in Minnesota, for example, found exposure to the pollutant particulate matter, PM2.5, raised the risk of Parkinson's disease by 36 percent.

Another study published earlier this year also found consuming at least 11 servings of ultra-processed food in a day increased the risk of early Parkinson's symptoms by damaging dopamine-producing neurons.

There is no cure for Parkinson's disease, but medications and other treatments can help replace lost dopamine and keep symptoms at bay.

The most common, Levodopa, crosses the blood-brain barrier to convert itself into dopamine, controlling balance issues and tremors.

The new study, published Tuesday in the journal PLOS Biology, looked at mice who were placed in soundproof chambers with noise coming out of speakers above the cages.

In one phase of the experiment, mice were exposed to the noise one time for one hour. In the second phase, the sounds went off for one hour per day for seven days total.

The noises were played randomly for five to 30 seconds at a time at varying intensities.

The team found that the noise exposure and chronically activating the inferior colliculus, which sits on the brainstem, reduced levels of a protein called vesicular monoamine transporter (VMAT) 2. VMAT 2 transports neurotransmitters like dopamine, serotonin and norepinephrine into neurons.

The noise also killed cells in the substantia nigra that produce dopamine, leading to movement issues like poor balance.

However, inhibiting the inferior colliculus lead to the production of additional VMAT 2, which the team said could reverse the harms of noise exposure in mice with early Parkinson's.

While the study was in mice, and there may be additional areas of the brain involved in this process, the results suggest a connection between the brain's sound processing areas and those that become damaged in Parkinson's.

The authors said: 'It was particularly fascinating to observe how the environmental noise-induced dopaminergic neurodegeneration and motor deficit, offering new insights into non-genetic risk factors for Parkinson's disease.'