It is not just the pollution caused by traffic that is affecting our health, but also the noise according to a new European study, which found that exposure to excessive traffic noise is linked to a higher risk of heart disease.

Led by Dr. Yutong Cai from Imperial College London, the new study looked at data from 144,000 adults in Norway and the Netherlands, and compared their exposure to levels of air pollution and traffic related noise to levels of blood biological markers, which are often used to assess the risk of heart disease.

Although air pollution has already been linked to an increased risk of heart disease, stroke, asthma, and risk of death, and noise pollution linked to raised blood pressure, disturbed sleep, and an increase in stress hormones, until now little research has been carried out on the effects of noise pollution and air pollution -- which are often found together -- on health.

Defined as noise louder than conversation level -- around 60 decibels (dB) -- noise pollution mainly affects those living near busy roads, under flight paths, or those who are exposed to industrial machinery.

To look at its effect on health the researchers tested the participants' blood for a range of biological markers that could indicate heart disease, including C-reactive protein (CRP), a protein that indicates inflammation and can lead to health problems like heart disease, lipids and triglycerides, which are linked to heart attacks when found at higher levels, and blood sugar levels, which are linked to heart disease, diabetes and stroke at higher levels.

After taking into account lifestyle factors which could change levels of these biomarkers, such as age, sex, education, employment, alcohol consumption, and smoking status, the team found that an increase of just 5dB in noise levels was linked to 0.3% higher blood sugar levels than those living in quieter neighborhoods.

In addition, a 10 µg/m3 increase in air pollution levels was also linked to 2.3% higher blood sugar levels, a 2.6% increase in CRP levels, and a 10% increase in triglycerides independently of noise pollution, suggesting that both air pollution and traffic noise are having a negative effect on health.

As well as causing an increase in the biological markers in the blood, the team also believe noise could be increasing the risk of heart disease by causing long-term psychological stress due to lack of sleep and an increase in the production of stress hormones.

The team now plan to carry out further research focusing on the effect of air and noise pollution to add to the limited body of research in this area.

The findings can be found published online in the European Heart Journal.