About 8,000 women were recruited to the Renfrew and Paisley study from 1972 to 1976. Of these, 40% had never smoked.
The authors, led by Dr Laurence Gruer from NHS Health Scotland, found 60% of non-smokers were overweight or obese compared with 40% of those who smoked.
The study claimed extra weight acted as a major contributor to premature death.
However, experts stressed that smoking was a “much stronger” risk factor than obesity.
The study of women aged 45 to 64, published in the British Medical Journal, said the highest rate of obesity among non-smokers was found in low income groups.
Almost 70% of women in this category were overweight or obese, according to the research.
Dr Gruer said: “You can certainly assume that if you are obese, you are more likely to die of things like diabetes, heart attacks and strokes.”
Researchers also suggested declining numbers of female smokers over the past few decades may have had a direct impact on obesity levels – with fewer people using cigarettes in an attempt to suppress their appetites.
The study also found that non-smokers from a lower occupational group were no more likely to die early if they lived a healthy lifestyle.
Dr Gruer said: “If you never smoke and you keep your weight within the reasonable limit then even if you earn below average income and live in a more disadvantaged area, you can still expect to live a long and healthy life.
“You are not doomed to die early just because you happen not to have a high income or good job or live in a leafy suburb.
“It goes against the idea that if you live in a poor neighbourhood or came from a working class background, then your health will be worse, regardless.”
Prof Johan Mackenbach from the Erasmus Medical Centre in Rotterdam welcomed the study but added: “It is important not to forget that smoking is a much stronger risk factor for mortality than most other risk factors, including obesity.”
Source: BBC
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