Quitting Smoking Ups Short-Term Risk of Type 2 Diabetes in ARIC Analysis

January 06, 2010

January 6, 2010 (Baltimore, Maryland) — Smoking increases the likelihood of developing type 2 diabetes, and the longer one smokes, the greater the risk; but smokers who quit may be raising their short-term risk of developing diabetes even higher [1]. Those conclusions came from a long-term follow-up of participants in the Atherosclerosis Risk in Communities (ARIC) study, reported in the January 5, 2010 issue of the Annals of Internal Medicine.

The analysis further suggested that the jump in diabetes risk after smoking cessation reaches its peak within about three years but stays elevated for at least another six years and appears to be at least partly promoted by weight gain.

That smoking ups the risk of diabetes has been widely observed, but the effect of quitting on risk has been far less thoroughly explored, observed the study's lead author, Dr Hsin-Chieh Yeh (Johns Hopkins University, Baltimore, MD) for heartwire . The current study may feature the longest follow-up time among the few that have pointed to greater diabetes risk after smoking cessation, she said.

As for the public-health message, Yeh affirmed that not starting to smoke is always best. For people who do smoke, the benefits of quitting are well recognized. Still, "in the short term, the patient and the physician should pay additional attention to weight management and weight control." She said she'd recommend counseling and other interventions to help quitters prevent weight gain through diet and exercise. "Another thing people may be able to do is check glucose levels more frequently after quitting, for earlier detection and early prevention of diabetes."

The authors looked at a cohort of up to 10 892 adults in the ARIC longitudinal study, which was based on sample populations from four regions across the US, who were free of diabetes and heart disease at baseline evaluation. As set by the ARIC protocol, participants returned to the clinic after about three years and then twice more at about three-year intervals, for a total of one baseline and three follow-up visits.

The risk of developing type 2 diabetes among smokers compared with those who had never smoked climbed with the number of pack-years.

Hazard Ratio (HR)* for Incident Type 2 Diabetes by Degree of Smoking in ARIC, in Pack-Years, vs Subjects Who Had Never Smoked

Pack-years HR (95% CI)
<13 1.09 (0.92–1.28)
14-30 1.38 (1.18–1.61)
>30 1.42 (1.20–1.67)
*Adjusted for race, sex, ARIC study center, education, baseline age, body-mass index, waist circumference, physical activity, triglyceride and HDL-cholesterol levels, and systolic blood pressure

In an analysis of the 9398 subjects who were free of diabetes at both baseline and their first follow-up visit, subjects classified as "new quitters"--that is, they were smokers at baseline but had quit before their first follow-up visit--showed a greater jump in adjusted risk of new diabetes at either visit 3 or visit 4 than subjects who had continued to smoke. When risk was further adjusted to account for change in weight, its increase was substantially blunted among new quitters but mostly unchanged among continuing smokers, Yeh et al reported.

Hazard Ratio (95% CI) for Diagnosis of Type 2 Diabetes (at ARIC Visits 3 or 4) Among 9398 Subjects Without Diabetes at Baseline or Visit 2, by Smoking Group vs "Never Smokers" (N=4090)

Analysis Former smokers, n=2910 "New" quitters, n=380 Continuing smokers, n=2018
Adjusted* 1.22 (0.99–1.51) 1.73 (1.19–2.53) 1.31 (1.04–1.65)
Further adjustment for weight change 1.22 (0.99–1.49) 1.53 (1.04–2.24) 1.34 (1.06–1.70)
*By age, race, sex, education, adiposity, physical activity, lipids, blood pressure, and ARIC study center

Further adjustment for leukocyte count, a marker of systemic inflammation, also attenuated the risk of new diabetes, but in both new quitters and continuing smokers, the group writes. "When simultaneously adjusted for both possible mediators [weight gain and leukocyte count], diabetes risk was markedly attenuated in new quitters and continuing smokers but essentially unchanged in former smokers."

The adjusted risk of diabetes was increased by 91% (95% CI 1.19-3.05) during the first three years after quitting smoking; it gradually decreased over the next nine years, reaching zero only at about year 12.

Emphasizing that smoking cessation has many positive health effects that outweigh the increased risk of diabetes highlighted in their analysis, Yeh et al caution that, nonetheless, "physicians should be aware of this elevated risk and should consider countermeasures, especially for heavy smokers."

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