This month 50 years ago, more than three times as many people as usual died in London over several days, due to the great smog. Stagnant weather conditions caused a sharp increase in the concentration of air pollutants - especially sulphur dioxide and smoke - leading to the premature death of 4,000 people.
A lot has changed since then; legislation has eliminated most of the air pollution of 50 years ago. In the Republic, the Tánaiste, Mary Harney, introduced the first ban on bituminous coal in 1990, covering the Dublin area. The ban has been gradually extended to other areas in the State; next year it will be extended once more to include Bray, Kilkenny, Sligo and Tralee, with the result that residents of most large urban centres will no longer be able to burn bituminous fuel.
Has the ban made a difference to people's health? According to a study published in the Lancet in October, it has. Prof Luke Clancy, consultant respiratory physician at St James's Hospital, Dublin, used the opportunity presented by the initial restriction on bituminous fuel to assess the effects of the sharp but sustained reduction in air pollution over Dublin. He and his colleagues found a 70 per cent reduction in air pollution as measured by black smoke. Respiratory deaths in the five years after the ban dropped by 15 per cent, while deaths from cardiac disease fell by 10 per cent.
The results strongly suggest that soot particles, sulphur oxides, or a combination of the two, damage the lungs and the heart. After screening out known predictors of death such as temperature changes and epidemics of lung infection, the authors estimate there are 243 fewer deaths from heart disease and 116 fewer respiratory deaths every year in Dublin following the ban on coal.
The way air pollution penetrates the respiratory system was brought home to me when I first studied anatomy. The cadavers of non-city-dwellers were easily distinguished from those who had lived in urban areas by the absence of black particles which collected throughout the lung. In extreme cases, the accumulated soot particles could easily be cut out from the lung tissue during the dissection process.
Although the presence of soot in lung tissue and the reduction in deaths noted by Clancy et al suggest that airborne particulate matter does indeed affect our health. The process and mechanism by which the heart and lungs are weakened are less straightforward.
Nitrogen dioxide induces inflammation within lung tissue; it has also been shown to impair the function of "scavenger" cells whose job it is to mop up lung infection. This would help explain the fact that air pollution has its greatest impact on people with pre-existing lung diseases such as asthma and chronic bronchitis.
Explanations for the link with heart disease have focused on the ability of certain pollutants to activate blood clotting and to cause inflammation within blood vessels. However, the exact significance of these processes in bringing about increased death from heart disease following air pollution has yet to be established.
What is not in doubt is the effect that the winter months have on patients with chronic obstructive pulmonary disease (COPD). Better known as chronic bronchitis or emphysema, the disease is responsible for 10 per cent of all hospital admissions here every year. But during the "clinical winter" - from November to March - there is a 45 per cent increase in the number of people admitted to hospital due to an exacerbation of their COPD, according to Dr Shane O'Neill, professor of respiratory medicine at Beaumont Hospital, Dublin.
The Republic was behind only Hungary when death rates from chronic bronchitis among 28 industrialised nations were calculated. "It is generally acknowledged that there are 110,000 sufferers of COPD in the Republic but this is just the tip of the iceberg," Prof O'Neill says, adding that people with COPD have been neglected by the medical profession and by the Government. "Given that the sufferers are usually old, from poorer socio-economic groups and that COPD has been caused by self-inflicted smoking, there has been a nihilistic approach to the disease."
WHILE smoking is the leading cause of chronic bronchitis and emphysema, exposure to air pollution is also a significant risk factor. So the legislative moves to ban coal sales over the past decade will have significantly helped many patients throughout the Republic.
Prof O'Neill was speaking at the launch of a new drug for COPD sufferers. Tiotropium has been shown to reduce the number of disease exacerbations and to increase patients' lung function. Taken as an inhaler, the new medication works to open up the diseased airway using a different mechanism to existing treatments.
Notwithstanding the beneficial effects of legislation to improve air quality, much work remains if the burden of chronic lung disease in particular is to be reduced. Moves to stop and prevent smoking are probably the most crucial; adding just 50 cent to a pack of 20 cigarettes as announced in the Budget falls well short of serious political resolve. If Harney, as a Government party leader, wanted to add to her reputation in the area of preventive respiratory and cardiac health, a taxation increase of at least €2 per pack would have been needed.
Dr Muiris Houston can be contacted at mhouston@irish-times.ie. He regrets he cannot answer individual queries.