HbA1c (Glycosylated hemoglobin)

Summary

• HbA1c shows your average blood sugar level over the last ~2–3 months, based on how much glucose has attached to hemoglobin in red blood cells.
• Both high HbA1c and unusually low HbA1c are linked to higher all-cause mortality in many studies (a U-shaped or J-shaped pattern).
• In adults without diabetes, the lowest risk is often observed around 5.0% to 5.7%.
• In many people with type 2 diabetes, the lowest observed mortality risk is often around 6.5% to 7.5%, but targets should be individualized.
• Large up-and-down swings in HbA1c over time are also linked to higher risk, even if the average value looks acceptable.

Factor description

HbA1c (also called glycated hemoglobin) is a blood test result reported as a percentage (%). It reflects the share of hemoglobin molecules in your red blood cells that have glucose attached.

Because red blood cells typically live about 90–120 days, HbA1c is a rolling average of blood sugar over roughly the past 2–3 months.

Measurement methods can vary:

• Lab HbA1c (most common): a standardized blood test.
• Point-of-care HbA1c: a faster clinic test that may be slightly less precise depending on device and setting.
• In special cases where HbA1c may be unreliable (for example, some anemia or hemoglobin variants), doctors may use other measures such as fasting glucose, oral glucose tolerance test, fructosamine, or continuous glucose monitor (CGM) metrics.

Impact on all-cause mortality

1. Why HbA1c can change long-term survival

• High HbA1c usually means long-term high blood glucose exposure.
• Chronic high glucose can damage blood vessels and organs over time, raising risk of complications that increase death risk (especially cardiovascular disease and kidney disease).
• HbA1c is also a strong signal of diabetes and prediabetes status, which are linked to higher all-cause mortality through multiple pathways.

2. What studies typically show (direction and shape)

• Many large cohort studies show a U-shaped or J-shaped relationship:
  • Higher HbA1c is linked to higher all-cause mortality risk.
  • Very low HbA1c can also be linked to higher all-cause mortality risk in some populations.
• In adults without diabetes, the lowest risk is often observed around 5.0% to 5.7%.
• In people with type 2 diabetes, the lowest observed mortality risk is often around 6.5% to 7.5%.
• The exact “best range” can differ by age, health status, medication regimen, and hypoglycemia risk.

3. Thresholds, plateaus, and practical interpretation

• Moving from clearly high HbA1c toward a moderate range is usually associated with lower risk.
• Below a certain point, “lower is not always better,” especially if low HbA1c is caused by frequent hypoglycemia or underlying illness rather than healthy glucose control.
• For people with diabetes, very aggressive targets may increase hypoglycemia risk, which can raise risk of injuries, heart rhythm problems, and other serious events.

4. HbA1c variability (stability over time)

• Studies commonly find that larger HbA1c swings over months/years predict higher all-cause and cardiovascular mortality, even after accounting for average HbA1c.
• A stable, realistic plan that reduces big fluctuations is often safer than chasing a perfect number.

5. How this links to major causes of death

• Cardiovascular disease: high HbA1c is associated with higher risk through atherosclerosis, inflammation, and vascular damage.
• Kidney disease: long-term high glucose can worsen kidney function, which increases all-cause mortality risk.
• Hypoglycemia-related events (in diabetes treatment): severe lows can contribute to injury risk and cardiovascular stress, affecting all-cause mortality.

Patterns

• Diabetes status matters: the HbA1c range linked to lowest observed mortality is often higher in people with type 2 diabetes than in people without diabetes.
• Older adults and people with multiple chronic conditions often need less aggressive HbA1c targets because the harm from hypoglycemia can outweigh benefits of tighter control.
• Lab interpretation can differ across populations when red blood cell turnover is altered (for example, anemia, recent blood loss, some hemoglobin variants, kidney or liver disease). In these cases, HbA1c may not match true average glucose.
• Some research notes that optimal screening cutoffs may vary by population (for example, some Asian cohorts have explored slightly different cutoffs to improve sensitivity), but clinical practice usually relies on standardized criteria.

KamaLama scoring

Scoring type: threshold-based, with a best range and penalties for higher-risk ranges. HbA1c is scored using category cutoffs because mortality risk often rises outside an optimal middle zone. Very low HbA1c is not scored as “extra benefit,” because studies often show no additional survival advantage and sometimes higher risk at unusually low levels. Unknown values are not scored.

Practical tips

• If you do not know your HbA1c, start with one test (often as part of routine blood work), especially if you have risk factors for diabetes.
• Focus on the simplest glucose-stabilizing habits first: regular meal timing, fewer sugary drinks, and more minimally processed high-fiber foods.
• Add movement you can repeat: a daily walk after meals and 2–3 days/week of basic strength work can improve glucose control.
• Aim for consistency, not perfection: reducing big swings (skipping meals, binge eating, irregular sleep) can help lower HbA1c variability.
• If you have diabetes and take glucose-lowering medication, avoid pushing HbA1c too low if it causes hypoglycemia; discuss targets that fit your age and health profile.
• If HbA1c seems unusually low or does not match your fingerstick/CGM readings, ask about alternative tests (fasting glucose, fructosamine, CGM metrics) and possible causes like anemia.

References

• Authoritative guidelines / evaluations

  • World Health Organization (WHO). 2011. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus. https://apps.who.int/iris/handle/10665/70523
  • American Diabetes Association (ADA). 2024. Diagnosis and classification of diabetes (Standards of Care in Diabetes). https://diabetesjournals.org/care/issue/47/Supplement_1

• Peer-reviewed / indexed research

  • Currie CJ et al. 2010. Survival as a function of HbA1c in people with type 2 diabetes. The Lancet. https://doi.org/10.1016/S0140-6736(09)61969-3
  • Huang ES et al. 2011. HbA1c and mortality in older adults with diabetes. Diabetes Care. https://doi.org/10.2337/dc10-2377
  • Inoue K et al. 2020. HbA1c and mortality risk in people without diabetes (cohort evidence). International Journal of Epidemiology. https://doi.org/10.1093/ije/dyaa263
  • Forbes A et al. 2018. Glycemic control and outcomes in type 2 diabetes (large-scale evidence). The Lancet Diabetes & Endocrinology. https://doi.org/10.1016/S2213-8587(18)30048-2
  • Li F et al. 2019. HbA1c and all-cause mortality (population evidence). The Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2018-02536
  • Rooney MR et al. 2020. HbA1c and mortality risk (population cohort evidence). Diabetologia. https://doi.org/10.1007/s00125-020-05285-3