High hourly levels of air pollution more than double the risk of one type of stroke, according to a Japanese report.

Currently, the risk of respiratory and cardiovascular problems tends to be linked to the average daily amount of air pollution, rather than variations in hourly levels.

In the current study, Kyoto University researchers analysed data on stroke deaths in people aged 65 years and older, occurring between January 1990 and December 1994 in 13 Japanese cities.

Levels of common air pollutants, including nitrogen dioxide, particulate matter and photochemical oxidants were monitored hourly at various sites.

The researchers found a seasonal link between particulate matter and intracerebral hemorrhage, where a blood vessel bursts inside the brain.

High hourly rates of particulate matter around two hours before death were associated with a more than doubling in the risk of death from a bleed into the brain.

This was much more common in the warmer months between April and September.

The findings held true, irrespective of the average daily level of air pollutants.

But the study could not find a link between high hourly levels of air pollution and ischaemic stroke, where the arteries in the brain become furred up and narrowed as a result of fatty deposits.

This is possibly because the time lag between the start of this type of stroke and death is rather longer than that for a bleed into the brain, say the authors.

Previous research showed that the effects of air pollution act quickly on the body, with inhaled particles detectable in the blood within 60 seconds. Peak levels can stay in the blood for up to an hour.

The study findings are published in the journal Occupational and Environmental Medicine.

The article High pollution levels double stroke risk originally appeared on 999 Today