Project objectives

Hypothesis

In diabetes, glycaemic control and blood pressure may become poorly controlled in the short to medium term following smoking cessation.

Purpose

To determine if there is cause to consider closer review of diabetic care and monitoring to achieve tightened glycaemic and hypertensive control at the time of stopping smoking in patients with diabetes. If so, the results will inform the design of an RCT for enhanced diabetes care during smoking cessation.

Research questions

1. What is the impact of smoking cessation on glycaemic control (HbA1c), risk factors for, and incidence of macrovascular and microvascular complications in smokers with diabetes who stop smoking over a 1 to 6 year period compared to those who continue to smoke?
2. What impact does relapse back to smoking subsequently have on these outcomes? (e.g. If ‘relapser’s show a reverse association to that following smoking cessation this would help us to establish causality).
3. How much does weight change account for the above associations?
4. Is there evidence of increased use of diabetes medications (a proxy measure of diabetes progression that is noticed and responded to by clinicians) following smoking cessation?
5. What are the success rates of smoking cessation among the diabetic population and what barriers to quitting need addressing?

Changes to project objectives

All of the above research questions were addressed, once we began working with the data we found that for practical reasons focus was greater in some areas than others.

Brief summary

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.

Findings

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, HbA1cincreased 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.

Interpretation

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.

Plain English summary

Sufferers of type 2 diabetes mellitus (T2DM) who quit smoking are likely to see a temporary deterioration in their glycaemic control which could last up to three years. We examined the primary care records of 10,692 adult smokers with T2DM over six years to investigate whether or not quitting was associated with altered diabetes control.

The study found that in the 3,131 (29%) people who quit and remained abstinent for at least one year, HbA1c2 – which is an average measurement indicating how well the body is controlling blood glucose levels – increased by 2.3mmol/mol (0.21%) before decreasing gradually as abstinence continued.

In the same period, 5,831 (55%) continual smokers – who did not change their smoking status during the study – experienced a more gradual increase in HbA1c, such that HbA1c levels in quitters became comparable with the levels seen in continual smokers three years after quitting.

We used a regression model which examined each cohort with and without weight change data, concluding that weight changes often associated with quitting smoking did not significantly alter the association between smoking cessation and HbA1c levels.

Previous research has shown that a 1% (11mmol/mol) reduction in the HbA1c level of someone with diabetes will result in them being 16% less likely to suffer heart failure and 37% less likely to experience microvascular complications – indicating the significance of small percentage changes in HbA1c levels.

Dissemination

Published articles

1. Lycett D, Nichols L, Ryan R, Farley A, Roalfe A, Mohammed M, Szatkowski L, Coleman T, Morris R, Farmer A, Aveyard P. The association between smoking cessation and glycaemic control in patients with type 2 diabetes: a THIN database cohort study. The Lancet Diabetes & Endocrinology 2015;3(6):423-430.
   http://dx.doi.org/10.1016/S2213-8587(15)00082-0

Conferences

1. NSPCR showcase 2014
2. EASD 2014

Public involvement

Public involvement was at the outset of study design. It was patients’ experiences of an unexpected deterioration in glycaemic control that led us to study this topic. Once we had the results it was clear from initial conversations with lay audiences that we had to frame our message carefully so that it did not detract in any way from the message to quit smoking.

Impact

We have had publication in The Lancet Diabetes and Endocrinology and presentation at several academic conferences.

We have had press and social media coverage from around the world

We have a specific message for clinicians, that it would be prudent to tighten diabetes control in preparation for and during the time of quitting. We hope to see this infiltrate into clinical guidelines in due course.

Further research on long term impact and the efficacy of enhanced care during this time is warranted.

This project was funded by the National Institute for Health Research School for Primary Care Research (project number 114)

Department of Health Disclaimer

The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR School for Primary Care Research, NIHR, NHS or the Department of Health.