Smokers who successfully quit may enjoy yet another health benefit: improved cholesterol profiles. A boost in “good” cholesterol comes with quitting despite weight gain after putting out the last cigarette, hints a new study.

If confirmed in future research, the finding could shed light on the strong, yet somewhat mysterious relationship between smoking and heart health. Up to 20 percent of heart disease deaths are currently blamed on smoking, but researchers haven’t yet had a clear understanding of what lies behind the effect. Smoking likely affects the cardiovascular system in a variety of ways, including lowered oxygen levels and wear and tear on the heart itself.

Some small studies have also shown that smoking lowers good cholesterol (HDL) and raises bad cholesterol (LDL), lead researcher Dr. Adam Gepner of the University of Wisconsin School of Medicine and Public Health, in Madison, told Reuters Health in an e-mail.

To test the impact of smoking on cholesterol levels more rigorously, and in a realistic setting, Gepner and his colleagues recruited more than 1,500 smokers representative of the current U.S. population, including its high proportion of overweight and obese individuals.

The average participant smoked about 21 cigarettes per day prior to the start of the study. After a year on one of five smoking cessation programs, 334 (36 percent) had succeeded in quitting.

The researchers found that those who stopped smoking experienced an average rise of about 5 percent, or 2.4 milligrams per deciliter (mg/dL), in HDL cholesterol.

Abstainers also experienced an increase in large HDL particles, which are important for lowering heart disease risk as well, report the researchers in the American Heart Journal.

The effects were somewhat stronger in women. However, it did not appear to matter how many cigarettes were smoked at the start of the study: heavy smokers enjoyed the same HDL benefit as lighter smokers after they quit.

One downside of kicking the habit can be weight gain. Sure enough, the group that quit gained an average of about 10 pounds compared to one or two pounds in the group that relapsed to smoking. Many participants were already overweight at the start of the study, with an average body mass index (BMI) of 29.6. (A BMI between 20 and 25 is generally considered healthy).

Adding pounds is known to hurt cholesterol levels, both raising the bad kind and lowering the good kind. As a result, the researchers think the weight gain might have offset some of the beneficial effects seen in the abstainers.

“Further benefits on cholesterol levels may have been actually masked by the weight gain seen after quitting,” explained Gepner.

“It is important to counsel quitters about weight gain and the need for a healthy diet and regular exercise during the quitting period,” he added.

The researchers caution that their results don’t prove that smoking cessation causes improvements in cholesterol. Further research is needed to rule out other possible explanations, including the role of changes in alcohol consumption, which is known to affect HDL.

Gepner also noted that it remains unclear exactly how smoking cessation might affect cholesterol levels, although it could have to do with changes in the proteins that control the breakdown of cholesterol. Smoking can damage these proteins.

Regardless, benefits were seen that might translate into better heart health.

Previous studies have shown, for example, that for every 1 mg/dL increase in HDL cholesterol, the risk of a cardiovascular event drops by up to three percent over 10 years.

Therefore, if the link holds, the improvements in blood lipids alone would decrease the average former smoker’s risk of a heart attack or stroke by up to 6 percent over the 10 years after they quit, said Gepner.

SOURCE: American Heart Journal, January 2011.