Introduction:

Although clinical trials have shown legacy effects of glycaemic control in diabetes, real-world data on historical glycaemic exposure and survival remain limited. This study assessed the impact of historical HbA1c levels on all-cause mortality in newly diagnosed type 2 diabetes (T2D) patients.

Methods:

• Design: Retrospective cohort (2000–2019)
• Population: 52,404 newly diagnosed T2D patients in Hong Kong
• Mean age: 58 ± 11 years
• 46% female
• Mean baseline HbA1c: 9.0% ± 2.5%
• Analysis:
  • 10-year mortality hazard functions
  • Weighted cumulative exposure model adjusting for confounders

Results:

Follow-up:

• Median: 6.3 years
• Deaths: 2,918

Key findings:

1. Sustained 1% HbA1c reduction over 10 years → 25% lower mortality risk (HR=0.75, 95% CI: 0.70-0.79)
2. Delaying HbA1c reduction to 5 years post-diagnosis → only 7% lower risk (HR=0.93, 0.87-0.99)
3. Critical time windows for achieving 1% HbA1c reduction:
   1. Years 1–2: 14% reduction (HR=0.86, 0.84-0.88)
   2. Years 3–4: 3% reduction (HR=0.97, 0.94-0.98)
   3. Years 5–6: 1% reduction (HR=0.99, 0.97-1.01)
   4. Years 7–8: 3% reduction (HR=0.97, 0.95-0.99)
   5. Years 9–10: 6% reduction (HR=0.94, 0.90-0.96)

Conclusion:

Both early and recent glycaemic exposures significantly influenced mortality risk in newly diagnosed T2D patients. The first 2 years post-diagnosis were critical, where at least a 1% HbA1c reduction yielded a 14% reduction in 10-year mortality. Intensive glycaemic control from diagnosis maximizes survival benefits.

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