Routine Blood Test May Offer Clues To Future Dementia Risk

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A study tracking 316,542 Korean adults found that people with very low hemoglobin—and, for some outcomes, very high levels—were more likely to receive a dementia diagnosis over as long as 15 years. The observational findings do not show that hemoglobin causes dementia or that changing its level would prevent it.

A study of 316,542 adults in South Korea found that hemoglobin levels recorded during routine health screening were associated with dementia diagnoses over as long as 15 years. The findings, presented at the 39th ECNP Congress and published in the Journal of Alzheimer’s Disease, suggest a possible link between a familiar blood-test measure and later dementia risk, but do not show that hemoglobin causes dementia.

The researchers grouped participants into five bands based on hemoglobin, a protein in red blood cells that carries oxygen. The adults were aged 40 or older and had national health screenings in 2004–2005. The team used national health insurance records to identify new dementia diagnoses through the end of 2019.

Compared with the group with the lowest dementia rate, participants in the lowest fifth of hemoglobin levels had a 16% higher risk of all-cause dementia. Those in the highest fifth had a 7% higher risk. These are relative risk differences reported by the researchers; the source report does not give the underlying absolute rates for these comparisons.

The pattern varied by diagnosis. For Alzheimer’s disease, the higher risk was mainly seen in the lowest hemoglobin group, at 14% above the reference group. For vascular dementia, the lowest group had a 19% higher risk and the highest group an 18% higher risk. The researchers said the vascular-dementia association did not follow a simple progression across all five groups. They also reported that the overall association was clearer and more consistent among women than men.

A Familiar Measure, a Long Follow-Up

Hemoglobin is already measured in many routine blood tests, so a possible association with later dementia could be examined using existing health records and warrants further study. The finding connects a marker of general physical health with brain-health outcomes across a large group followed for many years. It does not establish that the test can predict an individual person’s future or that using it to screen for dementia would improve care.

Lead researcher Dr Hyun Soo Kim, an assistant professor at Dong-A University College of Medicine, said the results may point to abnormal hemoglobin as a marker of wider physical vulnerability. He told the congress that the study does not show hemoglobin itself causes dementia. That distinction matters: the results cannot support changing a person’s hemoglobin level as a dementia-prevention strategy.

The report also highlights an unanswered research question: whether the association holds across populations beyond this large Korean cohort, and what it may reveal about the relationship between physical health and dementia risk. The findings are not a reason to interpret a routine blood result as a dementia diagnosis.

How Researchers Tracked Dementia

The study began with health-screening data from 2004–2005 and followed new diagnoses recorded in national insurance data through 2019. The maximum follow-up was about 15 years, though the source does not say every participant was observed for that full period. The analysis compared dementia outcomes among five hemoglobin groups rather than testing a treatment.

Hemoglobin can be low in people with anemia. The source report says unusually high levels may be associated with factors including smoking, dehydration, lung or heart disease, or other medical conditions. These possibilities underline why hemoglobin levels can reflect a range of health circumstances; the study does not identify one explanation for its observed associations.

Dr Lindsey Sinclair of the University of Southampton, commenting on the research, said evidence increasingly points to links between physical and brain health. She said further work is needed to establish whether the relationship appears in people from a wider range of backgrounds and what, if anything, could reduce risk among people with low or high 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

Association Does Not Show Cause

The research was observational, so it can identify patterns but cannot establish that low or high hemoglobin directly leads to dementia. The researchers also said early, undiagnosed dementia processes could affect nutrition, frailty, weight loss or anemia, potentially contributing to the association. The available report does not establish whether those factors account for the results.

It is also not clear whether the findings apply to populations with different backgrounds, or why the reported relationship was more consistent among women. For vascular dementia, the pattern across the five hemoglobin groups was not straightforward. The source provides relative differences but not the absolute dementia rates needed to show how large the difference was in practical terms.

Kim said the results should not be taken as advice to use iron supplements or deliberately raise or lower hemoglobin to prevent dementia. People with an abnormal test result should discuss it with a doctor, he said, because it may point to an underlying health issue.

Further Study Before Any Screening Use

The next steps are to test whether the association appears in groups from a wider range of backgrounds and to investigate possible explanations for the different dementia patterns. Researchers would also need to determine whether hemoglobin offers useful information beyond other health factors before it could be considered for any dementia-risk assessment.

For now, the study reports a long-term association, not a clinical test for dementia and not a prevention recommendation. A hemoglobin result remains a measure that should be interpreted in the context of a person’s overall health with a qualified clinician.

Key Questions

Does a low hemoglobin result mean someone will develop dementia?

No. The study found a group-level association, not a way to predict whether a particular person will develop dementia. Many participants with low hemoglobin may not receive a dementia diagnosis, and the report does not provide an individual’s risk.

Did the study show that hemoglobin causes dementia?

No. It was an observational study, which can identify associations but cannot establish cause and effect. The researchers also noted that early dementia-related changes could affect factors such as nutrition or frailty.

Should people take iron supplements to reduce dementia risk?

No such recommendation follows from the findings. Lead researcher Dr Hyun Soo Kim specifically cautioned against taking supplements or trying to raise or lower hemoglobin to prevent dementia. Discuss an abnormal result with a doctor.

How many people were included, and how long were they followed?

The study included 316,542 South Korean adults aged 40 and older who had health screenings in 2004–2005. National insurance records were used to track new diagnoses through the end of 2019, providing up to 15 years of follow-up.

Were the findings the same for all types of dementia?

No. The association differed by diagnosis. The higher Alzheimer’s risk was mainly reported in the lowest hemoglobin group, while vascular dementia showed higher risks at both the lowest and highest ends. Researchers said the vascular pattern did not steadily increase across all five groups.

Source: rss