People who are exposed to higher levels of traffic pollution have a higher risk of heart attack for about six hours, researchers from the London School of Hygiene and Tropical Medicine reported in the BMJ (British Medical Journal). The authors say that those with diagnosed heart disease should try to avoid being in areas where traffic pollution levels are high.

The researchers added that rather than causing heart attacks, traffic pollution probably hastens them.

Krishnan Bhaskaran and team gathered data from the records of 79,288 individuals who had had a heart attack in 15 parts of the United Kingdom over the period 2003 to 2006. Areas included Liverpool, London, Southampton, Sheffield and Cardiff.

They assessed local levels of traffic pollution in each area and found that the likelihood of having a heart attack was higher for a period of six hours after exposure to pollutants.

They plotted hourly levels of the following air pollutants:

  • PM10 (a is measure of particles in the atmosphere with a diameter of less than or equal to a nominal 10 micrometers)
  • Ozone
  • CO (carbon monoxide)
  • NO2 (nitrogen dioxide)
  • SO2 (sulfur dioxide)

Six hours after exposure, people’s risk of heart attack went back to normal, the authors wrote.

Bhaskaran said that traffic pollution is probably not a major contributing factor to heart attacks.

Bhaskaran said:

“If anything, it looks like it brings heart attack forward by a few hours. These are cardiac events that probably would have happened anyway.”

Associate Medical Director of the British Heart Foundation, Professor Jeremy Pearson, said:

“This large-scale study shows conclusively that your risk of having a heart attack goes up temporarily, for around six hours, after breathing in higher levels of vehicle exhaust.

We know that pollution can have a major effect on your heart health, possibly because it can ‘thicken’ the blood to make it more likely to clot, putting you at higher risk of a heart attack.

Our advice to patients remains the same – if you’ve been diagnosed with heart disease, try to avoid spending long periods outside in areas where there are likely to be high traffic pollution levels, such as on or near busy roads.”

Written by Christian Nordqvist