Lower car CO emissions, decreased suicide by exhaust gas correlated

January 01, 0001

Lower car CO emissions, decreased suicide by exhaust gas correlated

Globally, suicide accounts for 5.2% of deaths among persons aged 15 to 44 years and its incidence is rising. In Australia, suicide rates peaked in 1997 and have been declining since. A substantial part of that decline stems from a plunge in suicides by one particular method: asphyxiation by motor vehicle exhaust gas (MVEG). Although MVEG remains the second most common method of suicide in Australia, its incidence decreased by nearly 70% in the decade to 2006. The extent to which this phenomenon has been driven by national laws in 1986 and 1999 that lowered permissible levels of carbon monoxide (CO) emissions is unknown. The objective of this ecological study by researchers from Melbourne, Australia was to test the relationship by investigating whether areas of Australia with fewer noxious vehicles per capita experienced lower rates of MVEG suicide. They merged data on MVEG suicides in Australia (2001-06) with data on the number and age of vehicles in the national fleet, as well as socio-demographic data from the national census.

The annual incidence of MVEG suicides nationwide decreased by 57% (from 2.6 per 100,000 in 2001 to 1.1 in 2006) during the study period; the population density of pre-1986 and pre-1999 vehicles decreased by 55% (from 14.2 per 100 persons in 2001 to 6.4 in 2006) and 26% (from 44.5 per 100 persons in 2001 to 32.9 in 2006), respectively. The suicide rates were significantly and positively correlated with the presence of older vehicles. A percentage point decrease in the population density of pre-1986 vehicles was associated with a 6% decrease (rate ratio RR = 1.06) in the incidence of MVEG suicide within postcode areas; a percentage point decrease in the population density of pre-1999 vehicles was associated with a 3% decrease (RR = 1.03) in the incidence of MVEG suicide.

The researchers concluded: "Areas of Australia with fewer vehicles predating stringent CO emission laws experience lower rates of MVEG suicide. Although those emission laws were introduced primarily for environmental reasons, countries that lack them may miss the benefits of a serendipitous suicide prevention strategy."

Limiting CO emission levels from car exhausts appears to be related to a decrease in suicide by use of motor vehicle exhaust gas.

For the full abstract, click here.

PLoS Med 7(1): e1000210, published online 5 January 2010 (doi:10.1371/journal.pmed.1000210) © 2010 Studdert et al
Relationship between Vehicle Emissions Laws and Incidence of Suicide by Motor Vehicle Exhaust Gas in Australia, 2001-06: An Ecological Analysis. David M. Studdert, Lyle C. Gurrin, Uma Jatkar and Jane Pirkis.

Category: P. Psychological, Z. Social Problems Keywords: vehicle emissions, laws, incidence, relationship, suicide, motor vehicle, exhaust gas, Australia, ecological study, journal watch.
Synopsis edited by Dr Stephen Wilkinson, Melbourne, Australia. Posted on Global Family Doctor 11 February 2010

Pearls are an independent product of the Cochrane primary care group and are meant for educational use and not to guide clinical care.