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A long-term study of 316,542 Korean adults found that people in the lowest hemoglobin group had a higher rate of later dementia diagnoses than the reference group; elevated levels were also associated with higher risk for some outcomes. The observational findings do not show that hemoglobin causes dementia or that changing it prevents the disease.
A study of 316,542 adults in South Korea found that hemoglobin levels recorded in routine health screenings were associated with dementia diagnoses over as many as 15 years, researchers reported. The findings, presented at the 39th ECNP Congress and published in the Journal of Alzheimer’s Disease, point to a possible long-term health marker, but do not show that hemoglobin causes dementia or that altering levels can prevent it.
The researchers studied adults aged 40 and older who took part in South Korea’s national health screening program in 2004–2005. They divided participants into five groups according to their hemoglobin levels, from the lowest fifth to the highest fifth, then used national health insurance records to identify new dementia diagnoses through the end of 2019.
Compared with the study’s reference group—the group with the lowest dementia rate—participants in the lowest hemoglobin fifth had a 16% higher risk of all-cause dementia. Those in the highest fifth had a 7% higher risk. These are relative differences reported by the study, not a person’s absolute chance of developing dementia; the source report does not provide absolute risk figures.
Associations varied by diagnosis. For Alzheimer’s disease, the increased risk was mainly found among people in the lowest hemoglobin fifth, whose risk was 14% higher than the reference group’s. For vascular dementia, the lowest fifth had a 19% higher risk and the highest fifth an 18% higher risk. The vascular dementia pattern did not rise or fall in a simple way across all five groups. Researchers also reported that associations were clearer and more consistent among women than men.
Why Routine Blood Results May Matter
Hemoglobin is the protein in red blood cells that carries oxygen through the body. Because it is commonly measured in standard blood tests, an association with later dementia could give researchers a readily available way to investigate how physical health and brain health relate over time. The study drew on a large population and long follow-up, and its measure is already familiar to clinicians rather than requiring a specialist scan or a new test.
That makes the finding relevant to research and to conversations about overall health, but it does not make hemoglobin a dementia screening test. The study did not establish that a particular result can predict an individual’s future diagnosis, nor did it test whether treating an abnormal hemoglobin level changes dementia risk. The reported risk differences should not be read as evidence that a routine blood test can diagnose or prevent dementia.
Lead researcher Dr. Hyun Soo Kim, an assistant professor at Dong-A University College of Medicine, said the results suggest abnormal hemoglobin may be a visible marker of broader physical vulnerability. He stressed that the study does not show hemoglobin itself causes dementia. The distinction matters: low or high levels can be associated with other health conditions, and addressing those conditions is not the same as proving an effect on dementia.
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How the Korean Cohort Was Tracked
The analysis began with a national screening in 2004–2005, when the participants were at least 40 years old. Researchers grouped people by hemoglobin level and then followed health insurance records for new dementia diagnoses for up to 15 years, ending in 2019. This design let the team examine whether a routine measurement preceded later recorded diagnoses across a large group.
Hemoglobin levels can be affected by a range of factors. The report notes that low levels are commonly associated with anemia, while unusually high levels may reflect smoking, dehydration, lung or heart disease, or other medical conditions. Those possibilities reinforce why the observed relationship may reflect wider health circumstances rather than a direct effect of hemoglobin on the brain.
The work was presented at the European College of Neuropsychopharmacology Congress in Munich and published in the Journal of Alzheimer’s Disease. It is an observational study: researchers tracked measurements and later diagnoses rather than assigning participants to treatments intended to change hemoglobin.
“The findings do not show that hemoglobin itself causes dementia, but suggest that abnormal hemoglobin levels may be a visible marker of wider physical vulnerability relevant to brain health.”
— Dr. Hyun Soo Kim, lead researcher and assistant professor at Dong-A University College of Medicine
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What the Association Cannot Establish
The study can identify a relationship between screening results and later recorded diagnoses, but it cannot establish that low or high hemoglobin causes dementia. The source report does not provide absolute dementia risks for each group, and the findings do not show whether hemoglobin adds useful predictive information beyond other health factors. The reasons for the differences between women and men also remain unclear.
Reverse causation is another possibility raised by the researchers: early, undiagnosed dementia processes may affect nutrition, frailty, weight loss, or anemia, which could contribute to the pattern. The cohort was drawn from South Korea, so further research is needed to establish whether the associations hold in populations with different backgrounds and health circumstances. The study also did not test an intervention, so it cannot say whether treating anemia or high hemoglobin changes later dementia outcomes.
Kim said an abnormal hemoglobin result should be discussed with a doctor because it may point to an underlying health issue. The researchers specifically cautioned against taking iron supplements or trying to raise or lower hemoglobin as a dementia-prevention strategy on the basis of these results.
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Research Needed Beyond This Cohort
The next step is further research in people from a wider range of backgrounds to test whether the association is reproducible and to clarify how hemoglobin relates to other factors linked to dementia. Researchers would also need to determine whether hemoglobin meaningfully improves risk estimates and whether any health response to abnormal levels affects dementia outcomes.
For now, the finding is a research lead, not a new clinical recommendation. The study does not call for a special blood test, a change to routine screening, or a target hemoglobin level for dementia prevention. People with an abnormal result should discuss it with a qualified clinician, as the researchers advised, rather than attempting to change their levels based on this study.
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Key Questions
Does a routine hemoglobin test predict whether I will develop dementia?
No. The study found a group-level association between hemoglobin categories and later diagnoses; it did not establish a test that can predict an individual’s outcome.
Did low hemoglobin cause dementia in the study?
The study cannot show cause and effect. It was observational, and the researchers said abnormal hemoglobin may be a marker of wider physical health rather than a direct cause.
Should I take iron or try to change my hemoglobin to prevent dementia?
No such advice follows from these findings. Lead researcher Dr. Hyun Soo Kim specifically cautioned against taking iron or trying to raise or lower hemoglobin for dementia prevention based on the study. Discuss an abnormal result with a qualified clinician.
How long were participants followed?
The 316,542 participants had a screening in 2004–2005, and researchers tracked new dementia diagnoses through the end of 2019, for up to 15 years.
Did the findings apply equally to all types of dementia?
No. The reported associations differed for Alzheimer’s disease and vascular dementia. Researchers also said the relationship with vascular dementia did not follow a simple pattern across all five hemoglobin groups.
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