Can noisy traffic cause heart attacks?

“Living near loud traffic increases your risk of having a heart attack,” the Daily Mail today reported. The Mail added that the link “could be due to noise causing stress and sleep disturbances”. However, donning earplugs at night isn’t necessarily the answer to preventing heart attacks.

The Mail’s headline is based on a large urban Danish study showing that for every 10dB increase in the volume of road traffic noise exposure there was a 12 per cent increase in the risk of having a heart attack. This was the case for estimated traffic noise at the time of the heart attack and over the preceding five years.

This does not mean that traffic noise alone causes heart attacks. The authors speculated that higher noise exposure may increase stress and sleep disturbances, and that these in turn may lead to more heart attacks.

Similarly, the group that went on to have heart attacks was significantly less healthy than those who didn’t. While the researchers tried to adjust for this, there is still a chance that the association with road noise is just a coincidence.

This is an intriguing study. It highlights an association between traffic noise and the risk of heart attack, but it has not established cause and effect. The effect of traffic noise on the heart may be influenced by sleep disturbances or associated changes in lifestyle habits such as smoking, but these theories remain unproven and require further study.

The study was carried out by researchers from universities, societies and other research institutions based in Denmark and The Netherlands. It was funded by the Danish Environmental Protection Agency, the Research Centre for Environmental Health, Danish Ministry of the Interior and Health, and the Danish Cancer Society.

The study was published in the peer-reviewed science journal PloS One where the article is freely available online.

This was a large prospective cohort study that aimed to investigate the association between residential exposure to road traffic noise and the risk for new cases of heart attack that were not associated with air pollution and other known risk factors for heart attacks.

The study authors stated that both road traffic noise and ambient air pollution have been associated with risk for ischaemic heart disease. However, the evidence for this comes from only a few inconsistent studies that included both exposures. Ischaemic heart disease is characterised by a reduced blood supply to heart muscle that can cause symptoms of chest pain (angina) and decreased exercise tolerance.

The media reporting of this story was balanced, with coverage that included quotes from researchers suggesting that the relationship between traffic noise and heart attacks may be influenced by sleep disturbances. However, this is a theory put forward to explain the results, but has not been proven by this study alone.

The study was based on a cohort of 57,053 people who lived in the two largest Danish cities (Copenhagen and Aarhus) and who were born in Denmark. The participants were aged between 50 to 64 years old and were required to have no history of cancer when they enrolled in the study, which they did between 1993 and 1997.

At enrolment all the participants answered questions about food intake and lifestyle habits, including:

Trained staff members also measured blood pressure.

The participants were followed up until 2006 to document cases of heart attack and death that were obtained from linked medical and death records. On average people were followed up for 9.8 years, during which time researchers identified 1,600 cases of first-ever heart attack (myocardial infarction); 331 of which were fatal.

Exposure to road traffic noise and air pollution from 1998 to 2006 was estimated for all participants based on their residential address history. This estimation of noise exposure, measured in decibels (dB), used a noise-modelling programme called SoundPLAN, which the researchers said has been the standard method for noise calculation in Scandinavia for many years. This included inputting many measures of traffic including average daily traffic, vehicle distribution, travel speed, width of the road, distance of the person’s house from the road and information about the building height. However, the researchers did not measure noise levels for each participant. No information was available for "noise barriers" either – it is unclear whether the researchers meant earplugs or similar devices, or traffic-calming measures.

Associations between expected exposure to road traffic noise and new cases of heart attack were analysed to account for the influencing effects of air pollution and other potential confounders including age, sex, education, lifestyle factors, railway and airport noise.

The analysis calculated the risk of heart attack for each single year of age in the person’s life, and the average risk over the five-year period immediately before the heart attack.

The final analysis was based on 50,614 participants whose addresses were known and met the enrolment criteria. The key results were:

Those that had a heart attack were more likely to have high exposure to traffic noise and air pollution in their lives. They had also reached a lower educational level and were generally more unhealthy at enrolment, having:

The researchers concluded: “Long-term residential road traffic noise was associated with a higher risk for MI [heart attack], in a dose-dependent manner.”

This large cohort study of Danish adults shows that people who went on to have a heart attack had a significantly higher exposure to road traffic noise in the five-year period preceding the heart attack, and that the increase in risk was proportionate to the amount of noise exposure.

This study had many strengths, including its large cohort size, prospective design, objective measures of heart attack occurrence and the relatively large number of heart attacks observed in the study period.

However, the study had some drawbacks that make it difficult to conclude firmly that experiencing traffic noise increases your risk of heart attack. These include:

The group that went on to have heart attacks was significantly less healthy than those who didn’t (they smoked and drank more, and did less activity). While the researchers made every effort to adjust for this fact in their statistical analysis, there is still a chance that some of the observed increase in risk associated with noise exposure is in fact due to that group having a much less healthy lifestyle in general.

The study authors acknowledged that the study population was not representative of the wider Danish population as the participants lived mainly in urban areas. The study findings may not be directly applicable to people living in more rural areas and other countries outside Demark.

This intriguing study highlighted an association between traffic noise and the risk of heart attacks. However, there is no proven causation yet established. The effect of traffic noise on the heart may be influenced by sleep disturbances or associated changes in lifestyle habits such as smoking, but these theories remain unproven and would require further study.

The best way to avoid having a heart attack is to steer clear of risk factors such as smoking and eating a salty, fatty diet. Make sure you also get plenty of exercise. It is too early to recommend moving to a quieter neighbourhood or sleeping with earplugs in.

Analysis by Bazian. Edited by NHS Choices.