Researchers: Tougher exhaust standards reduced stroke deaths

Along with cleaner air, researchers found one other major benefit after the Tokyo metropolitan government tightened standards on exhaust emissions from diesel vehicles in 2006: a decline in deaths attributed to strokes.

The stroke death rate declined 8.5 percent in Tokyo’s urban areas after the tougher regulations were enacted in 2006, research showed. The drop means that 632 people annually were spared from dying following a stroke in the capital’s 23 wards.

The health ministry estimates that the stroke death rate will drop by 6.4-8.5 percent if the Japanese population’s average blood pressure is lowered by about 2 points.

“That would mean that the number of people dying of strokes will decrease by about 10,000 across Japan,” said Yoshihiro Kokubo, who heads the Department of Preventive Cardiology at the National Cerebral and Cardiovascular Center. “Reducing air pollution has health benefits on par with lowering blood pressure.”

The research team, led by Takashi Yorifuji, associate professor of epidemiology at Okayama University, said that the drop in stroke deaths may be connected to a decline in the pollutants in the air known as “particulate matter” (PM) 2.5.

The atmosphere contains fine particles, including nitrogen oxide and other pollutants.

Exposure to PM 2.5, particles that are less than 2.5 micrometers in diameter and about one-10th the size of pollen, are believed to raise the risk of cardiovascular disease such as strokes, in addition to respiratory disease, after they are inhaled and circulated throughout the entire body.

The team compared stroke deaths in the wards with concentration levels of PM 2.5, recorded by the metropolitan government, daily for 33 months before and after the new emission standards for diesel vehicles took effect in April 2006.

The concentration of PM 2.5 dropped to 15.9 micrograms per 1 cubic meter in 2009, down from 27.5 micrograms in 2002. One microgram is one-millionth of a gram.

The number of people who died of strokes stood at 19,728 over 33 months after the tougher diesel emission standards were introduced, compared with 20,460 over 33 months before the tightened regulations.

A decline of 8.5 percent in the stroke death rate was arrived at after factors were taken into consideration such as a trend in stroke mortality rates around the country, temperature and humidity, and the number of flu and heat stroke patients.