A new study cautions that inactivity is twice as deadly as being obese, but the risk of early death can be reduced by doing a little bit of exercise per day. 

Exercise is always on the to-do list that doctors recommend to people who need to shed off unhealthy pounds, and if you are one of those who is ignoring your doctor's advice, you might want to reconsider.

Researchers from the University of Cambridge found that lack of exercise is even deadlier than obesity. 

Elf Ekelund, study leader and a senior investigator scientist in the Medical Research Council Epidemiology Unit at the University of Cambridge, and his colleagues looked at the data of more than 334,000 men and women. During the 12-year follow-up period, they tracked the participants' body mass index (BMI) and self-reported levels of physical activity.

The findings showed that those who had the lowest level of physical activity were twice as likely to die at a younger age than those with clinical obesity. The results remained consistent even for those considered normal or overweight, but not exercising at all.

"The greatest risk [of an early death] was in those classed inactive, and that was consistent in normal weight, overweight and obese people," Ekelund told BBC News.

The good news is that even a little bit of exercise, such as a 20-minute brisk walk per day, can lower the chance of early death. The study highlighted the importance of exercise not only to lose weight, but also to prolong life span.

"The message from this study is clear and simple -- for any given body weight, going from inactive to active can substantially reduce the risk of premature death," Dr. David Katz, director of the Yale University Prevention Research Center, who is not part of the research, told HealthDay News.

The study was published in the Jan. 14 issue of the American Journal of Clinical Nutrition.