The association between smoking cessation and glycaemic control in patients with type 2 diabetes: a THIN database cohort study.
BACKGROUND
Smoking increases the risk of developing type 2 diabetes. However, several population studies also show a higher risk in people 3-5 years after smoking cessation than in continuing smokers. After 10-12 years the risk equates to that of never-smokers. Small cohort studies suggest diabetes control deteriorates temporarily during the first year after quitting. We examined whether or not quitting smoking was associated with altered diabetes control in a population study, for how long this association persisted, and whether or not this association was mediated by weight change.


METHODS
We did a retrospective cohort study (Jan 1, 2005, to Dec 31, 2010) of adult smokers with type 2 diabetes using The Health Improvement Network (THIN), a large UK primary care database. We developed adjusted multilevel regression models to investigate the association between a quit event, smoking abstinence duration, change in HbA1c, and the mediating effect of weight change.


RESULTS
10 692 adult smokers with type 2 diabetes were included. 3131 (29%) quit smoking and remained abstinent for at least 1 year. After adjustment for potential confounders, HbA1c increased by 0·21% (95% CI 0·17-0·25; p<0·001; [2·34 mmol/mol (95% CI 1·91-2·77)]) within the first year after quitting. HbA1c decreased as abstinence continued and became comparable to that of continual smokers after 3 years. This increase in HbA1c was not mediated by weight change.


CONCLUSIONS
In type 2 diabetes, smoking cessation is associated with deterioration in glycaemic control that lasts for 3 years and is unrelated to weight gain. At a population level, this temporary rise could increase microvascular complications.


BACKGROUND
National Institute for Health Research School for Primary Care Research.
Coventry University, Faculty of Health and Life Sciences, Coventry, UK. Electronic address: deborah.lycett@coventry.ac.uk.
Deborah
D
Lycett
School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
Linda
L
Nichols
School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
Ronan
R
Ryan
School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
Amanda
A
Farley
School of Health and Population Sciences, University of Birmingham, Birmingham, UK.
Andrea
A
Roalfe
University of Bradford, Bradford, UK.
Mohammed A
MA
Mohammed
School of Medicine, University of Nottingham, Division of Epidemiology and Public Health, Clinical Sciences Building, Nottingham City Hospital, Nottingham, UK.
Lisa
L
Szatkowski
School of Medicine, University of Nottingham, Division of Primary Care, Medical School, Queen's Medical Centre, Nottingham, UK.
Tim
T
Coleman
School of Social and Community Medicine, University of Bristol, Canynge Hall, Bristol, UK.
Richard
R
Morris
University of Oxford, Nuffield Department of Primary Care Health Sciences, New Radcliffe House Radcliffe Observatory Quarter, Oxford, UK.
Andrew
A
Farmer
University of Oxford, Nuffield Department of Primary Care Health Sciences, New Radcliffe House Radcliffe Observatory Quarter, Oxford, UK.
Paul
P
Aveyard
D000368:Aged; D001786:Blood Glucose / Q000378:metabolism; D015331:Cohort Studies; D016208:Databases, Factual; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000453:epidemiology / Q000628:therapy*; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012189:Retrospective Studies; D016540:Smoking Cessation; D013997:Time Factors; D016896:Treatment Outcome; D006113:United Kingdom / Q000453:epidemiology; D015430:Weight Gain / Q000502:physiology
D001786:Blood Glucose; D006442:Glycated Hemoglobin