Ozone modifies heart disease risk associated with high temperature

Ozone modifies heart disease risk associated with high temperature

By Caroline Price

22 November 2007

Occup Environ Med 2007; Advance online publication

MedWire News: High ozone levels in the atmosphere exacerbate the increase in cardiovascular (CV) mortality due to hot weather, study findings reveal.

"Concentrations of air pollutants, particularly ozone, are correlated with temperature.
Therefore, temperature and air pollution may interact to affect morbidity and mortality," explain C Ren (University of California, Irvine, USA) and colleagues.

Having previously demonstrated that air particulate matter modifies the association between temperature and morbidity and mortality, the researchers specifically examined the effect of ozone on this relationship.

They analyzed data from the US National Morbidity, Mortality, and Air Pollution Study for 95 different geographical regions, containing nearly 100 million people, between June and September each year for the period 1987-2000.

As reported in the journal Occupational and Environmental Medicine, ozone levels ranged from a daily average of 36.74 to 142.85 parts per billion and average daily temperatures ranged from 20°C to around 42°C.

A total of 4 million myocardial infarctions or strokes occurred, and plotting daily deaths against temperature fluctuations during 1 day revealed that ozone was a common factor.

In general, ozone positively modified the associations between temperature and CV mortality, ie, the increase in CV risk with rising temperature was greater the higher the ozone level.

For all 95 communities, a 10°C increase in average maximum temperature on the current day was associated with an increase in CV mortality on the same day of 1.17%, 4.35%, 4.31%, and 8.31% across quartiles of ozone levels, from the lowest to the highest.

Corresponding increases in CV mortality after a 1-day lag across ozone quartiles were 0.80%, 3.73%, 4.35%, and 8.62%.

The authors reason that exposure to ozone may affect the airways and autonomic nervous system, making people more susceptible to temperature fluctuations.

They say that public health warnings should alert people to stay indoors and avoid exposure on days with high temperature and high ozone.

Rising temperatures and the impact of ozone are likely to become increasingly important as the world heats up as a result of global warming, they add.

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