Depressed smokers are more likely to kick the habit sooner if they indulge in more exercise and physical activities, a new study finds.

Previous studies have established that smokers diagnosed with depression are likely to smoke twice as much as smokers without the mental disorder. This makes it more difficult for them to kick the habit. Researchers from the University of Concordia found that such individuals can quit smoking more quickly if they indulge in more exercise and physical activities.

"The review should be seen as a call to arms," said study co-author Grégory Moullec in a press statement. "Our hope is that this study will continue to sensitize researchers and clinicians on the promising role of exercise in the treatment of both depression and smoking cessation."

Alternatively, researchers also found that people who have a tough time kicking their habit of smoking should consider seeing a doctor to diagnose any cases of depression.

"We still need stronger evidence to convince policymakers," said Moullec. "Unfortunately there is still skepticism about exercise compared to pharmacological strategies. But if we continue to conduct ambitious trials, using high-standard methodology, we will get to know which interventions are the most effective of all."

Smoking causes both immediate and long-standing effects on exercise and physical activity. In addition to increasing the well-known risks for cancer and heart and respiratory diseases, smokers have less endurance, poorer physical performance and increased rates of injury and complications from physical activity.

To achieve peak performance, your heart, lungs and muscles need oxygen-rich blood. When you inhale tobacco smoke, carbon monoxide binds to red blood cells, displacing oxygen which prevents its delivery to the muscles and other body tissues. This causes an increase in lactic acid (the substance that causes muscle "burning," fatigue, heavier breathing, and increased soreness after exercise), a 1996 study pointed out.

This decrease in oxygen will reduce your physical endurance, making it more difficult for you not only to do well in sports but also to do everyday things, such as walking up stairs. This decrease in oxygenation causes a smoker's resting heart rate to be higher than a non-smoker's, as the heart must work harder to deliver adequate oxygen to the body.

The current study was published online in the journal Nicotine & Tobacco.