HbA1c

Optimal HbA1c and Longevity

What your long-term blood sugar says about life expectancy

TL;DR

  • HbA1c reflects your average blood sugar over about 2–3 months.
  • Mortality risk follows a U/J-shape: very high and very low HbA1c levels are both linked to higher all-cause mortality.
  • For most adults with type 2 diabetes, lowest mortality is seen around 6.5–7.5%.
  • For adults without diabetes, lowest mortality is typically 5.0–5.7%.
  • Big swings in HbA1c over time also predict higher risk, even if your average looks okay.
  • Targets should be individualized for age, comorbidities, and hypoglycaemia risk.

What HbA1c is and why it matters

HbA1c is the percentage of haemoglobin with sugar attached. It rises when blood glucose stays high and falls when glucose is well controlled. Because red blood cells live about 90–120 days, HbA1c captures a rolling average of glycaemia. It is used to diagnose diabetes, track treatment quality, and estimate long-term complication and mortality risk.

Diagnostic ranges and common targets

CategoryHbA1c (%)Typical use
Normal<5.7Population screening
Prediabetes5.7–6.4Higher future diabetes risk
Diabetes (diagnosis)≥6.5ADA/WHO standard
Common management target (many adults with T2D)<7.0Individualize for age and comorbidities
Alternative target range suggested by some groups7.0–8.0Older, frail, or hypoglycaemia-prone patients

Some Asian cohorts favour slightly lower diagnostic cutoffs (around 6.1–6.3 for diabetes; 5.65–5.9 for prediabetes) to improve sensitivity. Assay standardization (IFCC/NGSP) has reduced, but not eliminated, lab differences.

HbA1c and all-cause mortality

PopulationLowest observed risk rangeHigher-risk zonesNotes
Type 2 diabetes~6.5–7.5%>8.0% and <6.0%U/J-shape across multiple large cohorts and meta-analyses
No diabetes~5.0–5.7%≥6.5% and <5.0%Very low HbA1c may reflect illness (anaemia, liver disease, malnutrition)

Key point: both extremes and high variability increase risk. Aim for moderate, stable control that fits the person, not just the number.

HbA1c variability matters

Large swings in HbA1c over years predict higher all-cause and cardiovascular mortality, independent of the mean. Reducing variability by simplifying regimens, improving adherence, addressing hypoglycaemia, and standardizing monitoring can improve outcomes.

How and when to test

  • Adults without diabetes and low risk: every 3 years as part of routine screening or sooner if risk changes.
  • Prediabetes: every 6–12 months to track progression.
  • On new or adjusted diabetes therapy: 3 months after a change, then every 3–6 months.
  • Stable diabetes control: every 6 months is reasonable.
  • Consider paired measures when HbA1c may be unreliable (anaemia, haemoglobin variants, kidney or liver disease): fasting glucose, oral glucose tolerance test, fructosamine, CGM metrics (time in range).

Practical tips to improve accuracy: check with the same lab when possible, confirm unexpected results, and interpret alongside symptoms and glucose readings.

Why very low < 5.0% HbA1c can be risky

Very low values in non-diabetic adults do not confer extra protection and can associate with higher all-cause mortality. Mechanisms include reverse causation or confounding by conditions that lower HbA1c independently of glucose (short red-cell lifespan, chronic illness). Always interpret low HbA1c in clinical context.

Management principles

  • Personalize targets: balance long-term protection with hypoglycaemia risk, comorbidities, and life expectancy.
  • Reduce variability: consistent nutrition patterns, medication adherence, and realistic stepwise changes.
  • Prioritize lifestyle foundations: fibre-rich diet patterns, regular activity, sleep, stress reduction, and weight management.
  • Pharmacotherapy: choose agents with proven cardio-renal benefits when indicated; simplify where possible to limit glycaemic swings.
  • Monitor trends: treat the trajectory, not a single number.

When to consider additional testing

SituationWhat to addWhy
Discordant HbA1c and glucoseFPG, OGTT, fructosamine, CGMRule out assay/physiologic confounding
Suspected anaemia or haemoglobinopathyCBC, iron/B12, variant screeningHbA1c may be artifactually low/high
High variability on clinic readingsCGM metrics (time in range, glycaemic variability)Targets day-to-day swings, not just averages

Key insights

  1. The relationship between HbA1c and all-cause mortality is U/J-shaped in most cohorts.
  2. Moderate, stable control outperforms aggressive targets that provoke hypoglycaemia.
  3. Individual context matters more than a universal goal.
  4. Very low HbA1c in non-diabetics is not a longevity strategy.
  5. Consistent measurement and reduced variability improve risk prediction and care.

References

  1. Currie C et al. 2010. The Lancet. https://doi.org/10.1016/S0140-6736(09)61969-3
  2. Li W et al. 2016. International Journal of Cardiology. https://doi.org/10.1016/j.ijcard.2015.09.070
  3. Forbes A et al. 2018. The Lancet Diabetes & Endocrinology. https://doi.org/10.1016/S2213-8587(18)30048-2
  4. Li F et al. 2019. The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2018-02536
  5. Huang E et al. 2011. Diabetes Care. https://doi.org/10.2337/dc10-2377
  6. Yu J et al. 2024. Scientific Reports. https://doi.org/10.1038/s41598-024-80116-8
  7. Raghavan S et al. 2019. Journal of the American Heart Association. https://doi.org/10.1161/JAHA.118.011295
  8. Song B et al. 2021. Nutrition & Metabolism. https://doi.org/10.1186/s12986-022-00682-4
  9. Zeng R et al. 2023. Journal of Clinical Medicine. https://doi.org/10.3390/jcm12072615
  10. Carson A et al. 2010. Circulation: Cardiovascular Quality and Outcomes. https://doi.org/10.1161/CIRCOUTCOMES.110.957936
  11. Inoue K et al. 2020. International Journal of Epidemiology. https://doi.org/10.1093/ije/dyaa263
  12. Lee S et al. 2020. Acta Diabetologica. https://doi.org/10.1007/s00592-020-01605-6
  13. Sheng C et al. 2020. Diabetes Care. https://doi.org/10.2337/dc19-2589
  14. Critchley J et al. 2019. Diabetes Care. https://doi.org/10.2337/dc19-0848
  15. Kaze A et al. 2020. BMJ Open Diabetes Research & Care. https://doi.org/10.1136/bmjdrc-2020-001753
  16. Takao T et al. 2014. Journal of Diabetes and Its Complications. https://doi.org/10.1016/j.jdiacomp.2014.02.006
  17. Lee S et al. 2021. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-021-00751-4
  18. Palta P et al. 2017. Diabetes Care. https://doi.org/10.2337/dci16-0042
  19. Sugimoto T et al. 2024. Diabetes Care. https://doi.org/10.2337/dc23-2324
  20. Rooney M et al. 2020. Diabetologia. https://doi.org/10.1007/s00125-020-05285-3
  21. Deo S et al. 2021. European Journal of Cardio-Thoracic Surgery. https://doi.org/10.1093/ejcts/ezab180
  22. Xie J et al. 2024. BMC Public Health. https://doi.org/10.1186/s12889-024-19545-z
  23. Heo G et al. 2023. Diabetes & Metabolism Journal. https://doi.org/10.4093/dmj.2022.0112
  24. Terauchi Y et al. 2023. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-023-01915-3
  25. Afghahi H et al. 2022. PLoS ONE. https://doi.org/10.1371/journal.pone.0262880
  26. Gu J et al. 2018. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-018-0739-3
  27. Dykun I et al. 2025. JACC: Advances. https://doi.org/10.1016/j.jacadv.2025.101624
  28. Cohen R et al. 2008. Blood. https://doi.org/10.1182/blood-2008-04-154112
  29. Laiteerapong N et al. 2018. Diabetes Care. https://doi.org/10.2337/dc17-1144
  30. Herrington W et al. 2018. The Lancet Diabetes & Endocrinology. https://doi.org/10.1016/S2213-8587(18)30050-0
  31. Rubio J et al. 2020. Journal of Clinical Medicine. https://doi.org/10.3390/jcm9093009
  32. Xu Y et al. 2021. eLife. https://doi.org/10.7554/eLife.69456
  33. Sinning C et al. 2021. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-021-01413-4
  34. Lu J et al. 2021. The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/clinem/dgab532
  35. Agarwal S et al. 2020. Diabetes Care. https://doi.org/10.2337/dc20-1543
  36. Morioka T et al. 2001. Diabetes Care. https://doi.org/10.2337/DIACARE.24.5.909
  37. Pei J et al. 2023. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-023-02026-9
  38. Papazoglou A et al. 2020. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-021-01232-7
  39. Funamizu T et al. 2020. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-020-00996-8
  40. Lupu L et al. 2022. Cardiovascular Diabetology. https://doi.org/10.1186/s12933-022-01529-1
  41. Liang K et al. 2014. Diabetes Technology & Therapeutics. https://doi.org/10.1089/dia.2014.0157
  42. Hong S et al. 2016. Diabetes & Metabolism Journal. https://doi.org/10.4093/dmj.2016.40.2.167
  43. Silverman R et al. 2011. Diabetes Care. https://doi.org/10.2337/dc10-0996
  44. Kaur G et al. 2020. PLoS ONE. https://doi.org/10.1371/journal.pone.0242415
  45. d’Emden M et al. 2012. Medical Journal of Australia. https://doi.org/10.5694/mja12.10988
  46. Kumar P et al. 2010. The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2009-2433
  47. Bao Y et al. 2010. The BMJ. https://doi.org/10.1136/bmj.c2249
  48. Sitasuwan T & Lertwattanarak R. 2020. BMJ Open. https://doi.org/10.1136/bmjopen-2020-041269
  49. Klein K & Buse J. 2020. Nature Reviews Endocrinology. https://doi.org/10.1038/s41574-020-00425-6
  50. Qaseem A et al. 2018. Annals of Internal Medicine. https://doi.org/10.7326/P18-0003
  51. Miedema K. 2004. Diabetologia. https://doi.org/10.1007/s00125-004-1453-0
  52. Bergman M et al. 2020. The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/clinem/dgaa372

Disclaimer: Educational content only; not medical advice. Summaries were compiled using the AI models and peer-reviewed studies.

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HbA1c insight | KamaLama