Key finding
In nondiabetic adults, glycated hemoglobin showed a J-shaped association with death from any cause, remaining significant after adjustment for fasting glucose, in the ARIC cohort (n=11,092)
Evidence & causal status
Strong
Causal support strong for diabetes/CVD risk; all-cause mortality relationship J-shaped, so causal direction less clear at low HbA1c
Caveats & limitations
Reliability / bias notes: J-shaped curve means very low HbA1c also carries excess mortality risk, likely reflecting reverse causation/frailty; overlaps with the separate diagnosed-diabetes question, so effects are kept modest to avoid double-counting the same underlying condition
This describes a population-level association from published research. It is not a prediction about any one individual, and association is not the same as causation unless stated otherwise above.