Quitting smoking and type 2 diabetes: what a Korean study found
An analysis of 209 698 adults links more years without smoking to fewer diabetes complications; it is observational and does not prove cause.
The journal JAMA Network Open released on Oct. 2, 2026 a study that tries to link the years without tobacco of people with type 2 diabetes to the complications that damage the body's smallest blood vessels. There are three: nephropathy affects the kidney, retinopathy the eye and neuropathy the nerves. It is a retrospective, observational cohort, so it shows an association and does not show that quitting tobacco prevents a complication.
The authors work in Seoul, at Kyung Hee University and at the Ewha Womans medical center, and used South Korea's national health insurance database. Follow-up ran to December 2023 and covered 209 698 adults diagnosed with type 2 diabetes between 2003 and 2013: 162 861 who never smoked, 11 848 former smokers and 34 989 who kept smoking. The average age was 57.2 and 61% were women.
The central comparison pitted former smokers, grouped by years without smoking, against those who kept smoking. With eight years or more without smoking, the risk was lower for every complication:
| Complication | Hazard ratio | 95% confidence interval |
|---|---|---|
| All combined | 0.81 | 0.70 to 0.95 |
| Nephropathy | 0.79 | 0.64 to 0.94 |
| Retinopathy | 0.59 | 0.36 to 0.97 |
| Neuropathy | 0.80 | 0.66 to 0.98 |
A ratio below 1 means lower risk. With six to seven years without smoking, the combined complications had a ratio of 0.88. At the other extreme, those who had gone under two years without smoking showed a higher risk of nephropathy, with a ratio of 1.12. The study does not explain that result, and the authors point to possible biases.
What the authors acknowledge
They did not have participants' glycated hemoglobin (HbA1c), so glucose control may have played a role. It is also possible that some people quit because they were already ill, that smoking status was not updated during follow-up and that history before 2002 is unknown. By sex, the associations were significant only in men, and estimates in women were imprecise. The work was funded by a Korean national biomedical big-data project and the authors declare no conflicts of interest.
On tobacco in general, the Centers for Disease Control and Prevention (CDC) of the United States hold that quitting is among the most important steps for improving health and that it is beneficial at any age. Their page, from May 2024, does not address diabetes in particular: the link to that disease's complications comes only from the Korean study.
The results apply to a specific group, adults with type 2 diabetes in South Korea, and it was not verified whether they hold for the Mexican population. The CDC's general statements are aimed at the general population.
