Possibly in less than five years, according to a new analysis of data from more than 100,000 women, conducted by the Harvard School of Public Health.

Women who kicked the habit were 13 percent less likely to die in the first five years than those who continued to light up. Twenty years after quitting, the risk of death dropped all the way to the level of a woman who had never smoked.

These rates of improvement differed for various causes of death; the rate of death from lung cancer, for example, went down 21 percent in the first five years after quitting, but it did not reach the level of a non-smoker for 30 years. The risks went down more quickly for death from coronary heart disease and stroke.

The data came from the landmark Nurses' Health Study; the new analysis is reported in the current Journal of the American Medical Association.