Quitting smoking benefits outweigh weight gain risk

“Quitting smoking cuts heart risk despite weight gain”, reports BBC News.

While stopping smoking is known to reduce the risk of cardiovascular diseases, it is also common knowledge that many people who quit, gain some weight.

The BBC reports on efforts by researchers to discover whether the health benefits of quitting are cancelled out by the health risks associated with weight gain. The researchers undertook a large long-term study into the impact of smoking patterns and weight gain on the risk of developing cardiovascular disease.

It found that for most people, quitting smoking was associated with a reduced risk of cardiovascular disease. Crucially, this effect was not significantly influenced by weight gain associated with quitting smoking.

However, this association was only found in people without diabetes. The picture for people with diabetes was less clear. This may be because there were far less people in this subgroup, making it less likely that statistically significant differences were able to be detected, even if they exist.

This research offers tentative evidence that the widely used smokers’ excuse that, ‘any benefit of quitting would be offset by the weight I gain’, is untrue.

Where did the story come from?

The study was carried out by a collaboration of researchers from medical and academic research institutions based in Boston, US, and was funded by The Swiss National Science Foundation as well as grants from foundations and health institutes.

The study was published in peer-reviewed The Journal of the American Medical Association (JAMA), and can be read in full for free (known as open access).

The BBC coverage was accurate and included informative quotes from the researchers and other experts, including advice on how to avoid weight gain when quitting smoking through using stop smoking aids such as inhalators, gum, or lozenges that may help “resist the temptation to reach for comfort food in the place of a cigarette”.

What kind of research was this?

Quitting smoking is known to significantly reduce the risk of developing cardiovascular disease, a leading cause of death in many countries. It is also known that some people gain weight when they quit smoking due to a combination of factors.

This research was a prospective cohort study investigating the theory that weight gain associated with quitting smoking may weaken the cardiovascular benefits known to be associated with quitting.

A cohort study is a good way of assessing this link because it allows researchers to track weight gain, smoking habits, and the development of cardiovascular disease over the course of a person’s life.

Researchers can then look at relationships between different risk factors earlier in the person’s life, such as smoking, and how this was associated with subsequent outcomes, such as the development of cardiovascular disease.

What did the research involve?

This research includes people taking part in the large community-based cohort known as the Framingham Offspring Study, which began in 1971. The current study includes 3,251 participants who were free from cardiovascular disease at follow-up in 1984 and were then followed to 2011.

Every four to six years, participants in the cohort were examined and asked about their smoking status. They were categorised as:

• smokers
• recent quitters (quit sometime in the last four years)
• long-term quitters (quit more than four years ago)
• non-smokers

The main health outcome of interest was the development of cardiovascular disease, which was assessed at the regular study examinations and by reviewing participants’ medical records for new diseases in the intervening periods. Cardiovascular disease included coronary heart disease, stroke, peripheral artery disease and heart failure.

A range of other health and demographic information was collected at each visit, such as weight, blood pressure, and family history of disease.

The analysis estimated the association between quitting smoking and the development of cardiovascular disease in the six-year period immediately after. They then tested whether weight gain (up to four years after quitting) following quitting modified the association between quitting smoking and risk of cardiovascular disease.

The four- and six-year time points were chosen for practical rather than medical reasons, as this was the minimum time between assessments in the cohort study where data was available.

The researchers reported they had a pre-specified analysis plan that focussed on whether the effects were the same in people with and without diabetes. Hence, the researchers reported results for people with and without diabetes separately. The rationale behind this was that they believed weight change following quitting smoking might have a different effect on cardiovascular disease risk in people with and without diabetes.  This could be in part because weight gain can make diabetes harder to manage, and diabetes is associated with poorer cardiovascular health.

What were the basic results?

After a mean follow up period of 25 years, 631 ‘instances’ of cardiovascular disease occurred in the 3,251 participants.

Weight gain

Over the four year period, people without diabetes who had recently quit smoking gained significantly more weight (average 2.7 kg, range -0.5kg to 6.4kg), compared to long-term quitters (0.9kg, range -1.4 kg to 3.2 kg), smokers (0.9kg, range -1.8kg to 4.5kg) and non-smokers (1.4kg, range -1.4kg to 3.6kg). A similar pattern was found in people with diabetes.

This showed the weight gain associated with quitting smoking seemed to reduce with the more time that elapsed after quitting.

Cardiovascular risk

In people without diabetes only, the incidence of cardiovascular disease (adjusted for age and gender) over the study period was:

• 5.9 per 100 person examinations in smokers (95% confidence interval (CI) 4.9 to 7.1)
• 3.2 per 100 person examinations in recent quitters (95% CI 2.1 to 4.5)
• 3.1 per 100 person examinations in long term quitters (95% CI 2.6 to 3.7)
• 2.4 per 100 person examinations in non-smokers (95% CI 2.0 to 3.0)

This showed that, in people without diabetes, the incidence of developing cardiovascular disease was highest in smokers, lowest in non-smokers and at an intermediate point in those who had quit smoking. The same pattern, but with higher incidence rates, was observed in those with diabetes.

The researchers adjusted the results for cardiovascular risk factors and found that for people without diabetes, recent quitters were 53% less likely than smokers to develop cardiovascular disease over the study period (hazard ratio (HR) 0.47, 95% CI 0.23 to 0.94). Long-term quitters without diabetes were 54% less likely than smokers to develop cardiovascular disease (HR 0.46, 95%CI 0.34 to 0.63).

These associations did not change significantly after further adjustment was made for the change in weight associated with quitting. This suggests that weight gain had very little effect on the relationship between smoking status and cardiovascular disease risk.

Importantly, among people with diabetes, there were similar point estimates in the reduction in risk, although these were not statistically significant. This means we can’t be completely sure from this study of the cardiovascular benefits of quitting smoking for people with diabetes.

How did the researchers interpret the results?

The researchers remarked that, “in this community-based cohort, smoking cessation was associated with a lower risk of CVD events among participants without diabetes, and weight gain that occurred following smoking cessation did not modify this association. This supports a net cardiovascular benefit of smoking cessation, despite subsequent weight gain.”

Conclusion

This research on 3,251 adults found that quitting smoking was associated with reduced risk of developing cardiovascular disease, and that this effect was not influenced significantly by weight gain associated with quitting smoking. However, this result was only statistically significant in people without diabetes. A similar relationship was observed for people with diabetes, but was not statistically significant.

The strengths of this study included its regular collection of data over a long period (average 25 years). However, the following limitations should be considered:

• Smoking status was self reported, which is less accurate than other commonly used methods which analyse the components of a person’s breath for signs of nicotine consumption.
• The exact time since quitting was not available to the researchers, so the definition of a quitter was based on participants reporting smoking status at successive study examinations (four to six years apart). Hence, any temporary change in smoking status (relapses from quitting) less than four years would be missed. Given that many people take more than one attempt to quit smoking, this kind of assessment may not give a particularly accurate picture of peoples smoking habits.
• The assessment of weight gain also suffered the same problem in that it was only assessed at four to six yearly intervals and so more short-term fluctuations were not factored in. Generally, problems in the accuracy of measuring smoking status and weight gain would have reduced the chance of finding an association between weight gain, smoking status and cardiovascular disease, if there was one.
• The finding that cardiovascular disease risk was not statistically reduced despite quitting in those with diabetes, only those without, is worth noting. The authors point to the fact that their study might not have been large enough to detect such a difference. They also highlight that the relative reduction in cardiovascular risks through quitting smoking were similar in people with and without diabetes, but only those without diabetes reached the threshold of statistical significance.
• While these explanations are plausible, they may not provide the full picture. The reasons for this difference in risk between people with and without diabetes are worthy of more in depth research and consideration.
• This research only looked at the development of cardiovascular disease, presumably as this was the most obvious disease category that could be influenced by weight gain. However, it would be interesting to see if the effect is similar in other diseases associated with smoking, such as cancer.

Overall, this research provides tentative evidence that the benefits of quitting smoking on reducing cardiovascular disease risk in people without diabetes are not affected by weight gain commonly associated with quitting smoking. This link was not as clear in those with diabetes.