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Quitting Smoking For 8 Years Linked To Fewer Diabetes Eye And Kidney Complications

A massive Korean study suggests the payoff for quitting smoking with diabetes takes years to show up, but it's real.

By Dr. Axe Editorial Team · October 6, 2026 · 1 source · Watch

A cohort study published October 2, 2026 in JAMA Network Open found that people with type 2 diabetes who quit smoking for 8 or more years had a 19% lower risk of developing diabetic nerve, eye, or kidney complications compared with people who kept smoking. The benefit did not show up right away and only became statistically meaningful after years of staying smoke-free.

209,698adults tracked

8+years to quit

Researchers analyzed national health insurance data from 209,698 adults with type 2 diabetes in Korea (average age 57.2, 61% female), following them from a final health checkup between 2009 and 2013 through the end of 2023. People were sorted into never smokers (162,861), quitters who stayed smoke-free across at least four repeated checkups (11,848), and continuous smokers (34,989).

Compared with people who kept smoking, those who had quit for 8 or more years had a 19% lower risk of any diabetic microvascular complication (adjusted hazard ratio 0.81), a 21% lower risk of diabetic kidney disease (0.79), a 41% lower risk of diabetic eye disease (0.59), and a 20% lower risk of diabetic nerve damage (0.80). Quitting for 6 to 7 years was linked to a 24% lower risk of nerve damage (0.76), but quitting for under 2 years was linked to a 12% higher risk of kidney disease (1.12). The incidence rate of any complication was 301.9 per 10,000 person-years among continuous smokers versus 237.6 per 10,000 person-years among those quit 8 or more years.

Smoking is known to damage small blood vessels throughout the body by driving inflammation and impairing the endothelium, the inner lining of blood vessels; this general mechanism is the background link between smoking and nerve, eye, and kidney damage in diabetes. The lower risk in this study reached statistical significance only among men; the female-only analysis was limited by a small number of events.

This is an observational study, meaning it shows a link, not proof that quitting itself caused the lower complication rate. People who quit for under 2 years may have already been getting sicker and quit because of it, while long-term quitters may have also exercised more and drunk less, which could explain part of the lower risk.

Complication Rate: 301.9 vs 237.6 Per 10,000 Person-Years

JAMA Network Open, 2026, Shin et al.

The study lacked blood sugar control data, smoking history before 2002, and any update on smoking behavior after the final checkup.

Dr. Axe’s Take

This lines up with basic vessel physiology. Smoking keeps small blood vessels inflamed, and diabetes already stresses those same vessels in the eyes, kidneys, and nerves. Stack the two together and I would expect recovery to take years once you quit. If you have type 2 diabetes and smoke, I would start now rather than waiting for a crisis, since benefits here took 6 to 8 years to show up. Support vessel lining with fatty fish, leafy greens and garlic, stay active daily, and work with your doctor on blood sugar control and cessation support.

— Dr. Axe

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Study summary

Who: 209,698 adults with type 2 diabetes in Korea; average age 57.2; 61% female; grouped into 162,861 never smokers, 11,848 quitters, 34,989 continuous smokers
Design: Retrospective nationwide cohort study using repeated national health checkups to classify smoking status, followed from a final checkup in 2009-2013 through December 2023
Dose: Not applicable; exposure was smoking cessation duration (less than 2, 2-3, 4-5, 6-7, or 8+ years) compared with continuous smoking
Primary result: Cessation for 8+ years linked to 19% lower risk of any diabetic microvascular complication (adjusted HR 0.81, 95% CI 0.70-0.95) versus continuous smoking; incidence 301.9 per 10,000 person-years in continuous smokers vs 237.6 per 10,000 person-years in 8+ year quitters
Secondary: 8+ years cessation: 21% lower kidney disease risk (HR 0.79), 41% lower eye disease risk (HR 0.59), 20% lower nerve damage risk (HR 0.80); 6-7 years cessation: 24% lower nerve damage risk (HR 0.76); under 2 years cessation linked to 12% higher kidney disease risk (HR 1.12)
Funding / conflicts: Supported by a grant of the National Bio Bigdata Project, funded by Korean government ministries and the Korea Disease Control and Prevention Agency; the paper says the funder had no role in the study. Conflict statement in the PubMed record: None reported.
Date: Oct 2, 2026