Date published: 2005/09/22
The BBC says:
Smoking just one to four cigarettes a day almost triples a person's risk of dying of heart disease, according to Norwegian researchers.
Their work suggests the health impact is stronger for women and that even "light" smokers face similar diseases to heavier smokers, including cancer.
The team tracked the health and death rates of almost 43,000 men and women from the mid 1970s up to 2002.
Their findings appear in the journal Tobacco Control.
Compared with those who had never smoked, the men and women who smoked between one and four cigarettes a day were almost three times as likely to die of coronary artery disease.
Among women, smoking one to four cigarettes daily increased the chance of dying from lung cancer almost five times.
Men who smoked this amount were almost three times as likely to be killed by lung cancer.
However, due to the relatively small number of men that this applied to in the study sample, this finding could have been due to chance.
...
The researchers believe their conclusions are accurate, even though they had to estimate the projected impact of smoking one to four cigarettes for five years in those light smokers who had smoked for less time.This indicated that the risk of death from coronary artery disease for both sexes would have been 7% higher, and the risk of lung cancer would have been 47% higher in women.
A significant proportion of the light smokers had also increased their daily consumption over the period of the study. However, this had not exceeded nine cigarettes a day.
Author Dr Kjell Bjartveit also pointed out that it was not possible to tell from the findings what impact sporadic smoking - such as a few cigarettes on a Saturday night out - might have on health.
Dr Ken Denson of the Thame Thrombosis and Haemostasis Research Foundation questioned the validity of the figures.
He said other large studies had not found that smoking fewer than 10 cigarettes daily increased the risk of heart disease.
A classic confusion of correlation and causation. Of course it's possible the small amount of smoking was the cause of the increased health problems, and certainly most people would believe this, which is why the authors can get away with making these assertions so easily. But the authors do not prove any causation, they just prove a correlation. To prove a causation you would have to take a random sample of people and force half to smoke a few cigarettes a day and the other half not to smoke at all, and see what the difference was. Needless to say, health studies are never done this way. As an example of what can be wrong with the simple "smoking is evil" conclusion of the study, in the UK these days smokers tend to be from the "lower" sociodemographic classes, and these classes generally have worse health problems for all sorts of reasons. Hopefully the study factored this out. And you also have to be cautious about anything published in a journal which is openly hostile to tobacco.
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