Several studies have found exercise can help women control nicotine cravings during controlled experiments, but outside those controlled confines, the effect fizzles out.

A new study from Brown University in Rhode Island says that's because exercise often falls by the wayside, and the craving returns.

Lead researcher David Williams said women need to keep exercising frequently in order to curb the cravings.

The researchers followed 60 female smokers during an eight-week program to quit smoking.

They were all given counselling and nicotine patches. Half were assigned to the exercise group, in which they briskly walked on a treadmill at the study centre for 50 minutes three times a week. The other 30 women watched 30-minute health and wellness videos three times a week.

The researchers asked the participants in each group about their mood and cigarette cravings immediately before and after each session.

The researchers found those who exercised were more likely to experience improved mood and decreased cigarette cravings than those in the other group, but these effects dissipated by the time of their next exercise session.

Williams said it was good to see exercise helped, but it clearly wasn't sustained, even over a matter of a few days.

But, he said, the cravings went away again after exercise.

"One implication for these findings is that exercise may be a useful treatment strategy, but it has to be done frequently enough and consistently enough because the effects that it has diminish over time," Williams said.

The study appears in the journal Addictive Behaviors.