CV benefits of smoking cessation not attenuated by resultant weight gain
Smoking Cessation, Weight Change, Type 2 Diabetes, and MortalityLiterature - Hu Y, Zong G, Liu G et al. - N Engl J Med 2018; 379:623-632
Introduction and methods
Although smoking cessation decreases the risk of major chronic diseases and extends life expectancy , it may cause weight gain in quitters . Weight gain may discourage quitting attempts and attenuate health benefits of smoking cessation through increasing the risk of cardiometabolic disease and premature death . However, evidence regarding health consequences of weight gain after smoking cessation is contradictory [4-8], possibly due to unmeasured smoking behavior during follow-up . Moreover, a relapse within the next decade has been shown in >30% of quitters who were abstinent for one year .
This longitudinal study evaluated risk trajectories of disease and death in people who quitted smoking by measuring body-weight changes after smoking cessation. Secondary analyses studied the role of physical activity and diet in weight gain.
The study enrolled participants from three cohorts - the Nurses’ Health Study (NHS), the Nurses’ Health Study II (NHS II), and the Health Professionals Follow-up Study (HPFS) - without prevalent diabetes, cardiovascular disease (CVD), or cancer at baseline. A study sample of 162,807 participants could be analyzed for diabetes analyses and 170,723 participants for mortality analyses. Medical and lifestyle information was obtained by questionnaires every two years (one cycle) during follow-up. The role of physical activity and diet in weight gain were measured by using the metabolic equivalent tasks (METs) and Alternative Healthy Eating Index (AHEI), respectively.
Participants were classified according to smoking status and weight gain, discriminating between current smokers (smoking in previous and next cycles), recent quitters (2-6 consecutive years without smoking), and long-term quitters (>6 consecutive years without smoking), and weight gain of 0.1-5.0 kg, 5.1-10.0 kg, or >10 kg. The outcome was type 2 diabetes (T2DM), deaths from CVD, and all-cause mortality during a mean follow-up of 19.6 years.
- The association between smoking cessation and T2DM was modified by weight gain (P-interaction <0.001). Compared with current smokers, recent quitters without weight gain showed an HR of 1.08 (95%CI: 0.93-1.26). Those with weight gain of 0.1-5.0 kg, 5.1-10 kg and >10 kg showed HRs for T2DM of HR: 1.15; 95%CI: 0.99-1.33, HR: 1.36; 95%CI: 1.16-1.58 and HR: 1.59; 95%CI: 1.36-1.85, respectively.
- In a three-dimensional representation of risk of T2DM according to years since smoking cessation and weight change, a peak of diabetes risk was seen among quitters with the most weight gain at 5 to 7 years since cessation. A mediation analysis showed that weight change within six years after smoking cessation explained 68.4% (95%CI: 8.3-98.1) of the elevated risk of T2DM in quitters.
- As compared with current smokers, the HR for CVD death in recent quitters without weight gain was HR: 0.69 (95%CI: 0.54-0.88), and HR: 0.47, 95%CI: 0.35-0.63, HR: 0.25, 95%CI: 0.15-0.42, HR: 0.33, 95%CI: 0.18-0.60 for those with weight gain of 0.1-5.0 kg, 5.0-10.0 kg and >10kg, respectively. In longer-term quitters HR of CVD death, compared to current smokers was HR: 0.50 (95%CI: 0.46-0.55).
- HRs for all-cause death in recent quitters without weight gain, with weight gain of 0.1-5.0 kg, 5.0-10.0 kg and >10kg , compared to current smokers, were HR: 0.81 (95%CI: 0.73-0.90), HR: 0.52 (95%CI: 0.46-0.59), HR: 0.46 (95%CI: 0.38-0.55) and HR: 0.50 (95%CI: 0.40-0.63), respectively. Longer-term quitters compared to current smokers showed an HR of 0.57 (95%CI: 0.54-0.59).
- Each increase of ten METs hours per week in physical activities was associated with 0.13 kg (95%CI: 0.11-0.15) less weight gain, and each 10-point increase in AHEI-score was associated with 0.26 kg (95%CI: 0.21-0.32) less weight gain.
Benefits of smoking cessation on all-cause and CV mortality were not attenuated by substantial weight gain, even though this is associated with a temporarily increased risk of T2DM after quitting. Weight gain after smoking cessation can be reduced by physical activity and a healthy diet.