The conclusion was reached by researchers at the Universities of Glasgow and Stirling who examined data from more than 5,200 men and women living in the central belt of Scotland who were smoking when first recruited to two studies in the early 1970s.
All of the participants were re-contacted a few years later and asked again about their smoking.
Some had stopped altogether, some had reduced the number of cigarettes they smoked, while others had maintained or increased the level of their smoking.
The researchers found that, compared to maintainers, the quitters had lower mortality rates, but there was no significant difference between the reducers and the maintainers.
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In one of the two studies, a sub-group of the reducers who had been among the heaviest smokers at the start did show lower mortality rates but this was not seen in the other study.
The Scottish findings, published in the American Journal of Epidemiology, do not support those of a similar long-term study in Israel where smoking reduction did appear to reduce mortality rates, but are consistent with larger studies of shorter duration in Denmark and Norway where it did not.