Washington: Over 80 million American adults are putting themselves at serious risk of long-term illness and early death through smoking, obesity, or both, finds a study published on bmj.com.

Smoking and obesity are two of the leading causes of death and illness in the United States, but the overlap between the two conditions has never been measured.

Using data from the 2002 national health interview survey, researchers estimated the proportion of adults in the US who smoke and are obese. The results were stratified for various factors, such as income and education levels.

They found that 23.5% of adults were obese and 22.7% smoked (a total of 81 million).

About 4.7% (9 million) smoked and were obese. This proportion was particularly high in African Americans (7%) and in people with lower income and education levels.

Although this overlap is relatively low, the presence of these two conditions together may carry an increased risk to health, say the authors.

Treatments for people who smoke and who are obese need to be investigated, they add. Clinical trials should monitor the effects of programmes aimed at simultaneously stopping smoking and weight control. These results could be used to develop policies for prevention and treatment.