Two new studies point to yet more reasons to kick the tobacco habit. In one, researchers found quitting smoking is worth it for people with diabetes despite worries about potential weight gain. In the other, scientists discovered smoking might have a much greater impact on the cognitive function than originally thought. Both studies were presented at the American Heart Association's Epidemiology and Prevention | Lifestyle and Cardiometabolic Health Scientific Sessions 2019, a premier global exchange of the latest advances in population-based cardiovascular science for researchers and clinicians, held in Houston this week.

In the study on smoking cessation, weight change and the risk of developing or dying from cardiovascular diseases in people with diabetes, researchers analyzed detailed, long-term health information from two studies that included 10,895 men and women with diabetes. Overweight and obesity are risk factors for diabetes, and both diabetes and smoking tobacco are major risk factors for heart attacks, strokes and other cardiovascular events.

Researchers found the benefits of quitting smoking for people with diabetes significantly outweighed the risk of gaining weight, even though weight gain is a risk factor for cardiovascular disease. Compared to people with diabetes who continued to smoke, the risk for heart attacks, stroke and other cardiovascular diseases did not increase among recent quitters who gained up to 11 pounds (5.0 kg) or even those who gained more than 11 pounds. The risk for cardiovascular disease was 34 percent lower among recent quitters (six or fewer years since quitting) without weight gain; 25 percent lower among long-term quitters (more than six years since smoking cessation); and 41 percent lower among never-smoking adults with diabetes.

"Weight gain concerns should not stop people from being encouraged to quit smoking after they're diagnosed with diabetes. And for those who do quit, preventing excessive weight gain would further maximize the health benefits of smoking cessation," said Gang Liu, Ph.D., lead author of the study and a postdoctoral research fellow in the department of Nutrition at Harvard T. H. Chan School of Public Health in Boston.

A second study spotlights tobacco's link to cognitive decline in the general population. Cognitive decline means that a person's memory, reasoning and other mental functions are impaired over time.

Although tobacco use has been associated with a higher risk for cognitive decline, it's difficult to measure just how much of an impact smoking has because smokers are more likely than nonsmokers to drop out or die before the end of long-term studies, according to study author Aozhou Wu, M.H.S., a Ph.D. student in epidemiology at the Bloomberg School of Public Health at Johns Hopkins in Baltimore.

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"As a consequence, smokers' cognitive measurements in studies were likely to be missing in other studies because they're lost to follow-up," Wu said.

Wu and colleagues adapted a methodology that considers a smoker's likelihood of dropping out of a study or dying from tobacco-related causes during the study period to analyze the cognitive impact of tobacco use among 4,960 adults who were free of cognitive impairment at the study's start. Researchers followed the participants for about five years, with regular assessments of the participants' memory, language function and logical thinking ability.

When the researchers used the new study methods and compared people who never smoked tobacco to those who smoked a pack of cigarettes a day for 25 years or more, they found that the tobacco's harmful effect on cognition among the smokers was more than twice as much as they had observed using the traditional study methods.

Co-authors of Liu's study are: Yang Hu, Sc.D.; Geng Zong, Ph.D.; Frank B. Hu, M.D., Ph.D.; JoAnn E. Manson, M.D., Dr.P.H.; Kathryn M. Rexrode, M.D.; Eric B. Rimm, Sc.D.; and Qi Sun, M.D., Sc.D.

Co-authors of Wu's study are: A. Richey Sharrett, M.D., Dr.P.H.; Jennifer A. Deal, Ph.D.; Karen Bandeen-Roche, Ph.D.; Andreea Rawlings, Ph.D.; Melinda C. Power, Sc.D.; Alden L. Gross, Ph.D., M.H.S.; David Couper, Ph.D.; Michael Griswold, Ph.D., Thomas Mosley, Ph.D.; Rebecca F. Gottesman, M.D., Ph.D.; and Josef Coresh, M.D., Ph.D.

Author disclosures are on the abstracts.

The National Institutes of Health (NIH) funded both studies.