Low-Normal Hemoglobin Linked to Higher Mortality Risk Among Adults: Study
Haemoglobin levels that fall just above the usual threshold for anaemia may still be linked to a higher risk of death, according to a large UK study published in Annals of Internal Medicine.
Researchers from the University of Glasgow analysed data from 502,188 adults in the UK Biobank to examine how haemoglobin levels were associated with long-term mortality. Participants were followed for a median of 13.6 years, with researchers examining deaths from any cause, cardiovascular disease and cancer.
The study found a U-shaped relationship between haemoglobin levels and mortality. In simple terms, people with both very low and very high haemoglobin levels had higher mortality than those in the middle range.
The lowest risk was seen among adults whose haemoglobin concentration was 1 to 3 g/dL above the World Health Organization’s current sex-specific thresholds for anaemia. This means some people whose levels would usually be considered only borderline low may still have a higher risk compared with people in the range associated with the lowest mortality.
The findings could be important because haemoglobin is commonly used to identify anaemia, a condition in which the blood has a reduced ability to carry oxygen. Current thresholds help clinicians decide when further investigation or treatment may be needed.
However, the researchers stressed that the results do not mean the WHO’s anaemia thresholds should be changed. Instead, they suggest that borderline haemoglobin levels may deserve closer investigation, particularly when considered alongside a person’s overall health and other risk factors.
The study was prospective and involved a very large population, allowing researchers to examine long-term outcomes.
Further research is therefore needed to understand why mortality appears lowest within this haemoglobin range and whether people with borderline levels could benefit from additional clinical assessment.
REFERENCE: Malek Ahmad, John G.F. Cleland, Pasquale Maffia, et al. Association Between Blood Hemoglobin Concentration and Mortality by Age and Sex: A Prospective Cohort Study. Ann Intern Med. 2026. doi:10.7326/ANNALS-26-00057
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