A routine blood test might reveal something about dementia risk years before any diagnosis.
Not a specialized brain test or new genetic screen, but hemoglobin, the familiar number that measures an oxygen-carrying protein in red blood cells.
In a large study from South Korea, people at both ends of the hemoglobin range were more likely to receive a dementia diagnosis later on.
Yet the story changes when researchers separate Alzheimer’s disease from vascular dementia, and the lead researcher has a pointed warning for anyone tempted to change their hemoglobin level.
The findings, presented at a European neuropsychopharmacology congress in Munich, draw on health records from more than 316,000 adults. They also join a line of studies raising questions about how blood and brain health connect. Some findings echo one another; others don’t quite fit.
A Routine Screening Meets a 15-Year Follow-Up.
Researchers matched ordinary health checks from the early 2000s with diagnoses recorded years later.
In 2004 and 2005, participants aged 40 or older underwent national health screening that included a hemoglobin measurement. Researchers then tracked new dementia diagnoses through national health insurance records until the end of 2019, giving them up to 15 years of follow-up.
The team divided participants into five groups, from the lowest 20% of hemoglobin measurements to the highest 20%. This study, led by Dr. Hyun Soo Kim of Dong-A University College of Medicine in Busan, was recently published in the Journal of Alzheimer’s Disease.
What makes this interesting is how ordinary the starting point was. Hemoglobin testing is inexpensive and familiar, unlike specialist brain scans or newer biomarkers. The researchers didn’t need an additional test to examine the connection.
The Results Changed With the Type of Dementia
When split by dementia type, the pattern no longer looked like one simple line.
Across all dementia diagnoses, people in the lowest hemoglobin group had a 16% higher risk than those in the group with the lowest dementia rate. At the other extreme, the highest group had a 7% higher risk.
But the picture shifted when researchers examined specific types of dementia.
For Alzheimer’s disease, the 14% higher risk appeared mainly in the lowest group, with no corresponding figure reported for the highest. Vascular dementia, caused by reduced blood flow to the brain, showed a different pattern: 19% higher risk in the lowest group and 18% in the highest. Even then, the results across all five groups didn’t follow a simple progression.
Another wrinkle involved sex. The association was clearer and more consistent among women, although researchers provided neither sex-specific figures nor an explanation. That doesn’t mean the connection was absent in men.
Related: Why You Keep Walking Into Rooms and Forgetting Why
Why Those Percentages Come With Fine Print
A 16% higher risk is not a 16% chance of developing dementia.
These percentages describe differences between groups, not someone’s personal odds. Without reported absolute dementia rates, there’s no way to make that calculation.
There’s another distinction worth making. The “lowest fifth” refers to measurements within this Korean study population. Researchers didn’t provide blood-level cutoffs, so being in that group cannot automatically be interpreted as anemia.
And because the study was observational, it cannot establish cause and effect.
Kim cautioned in the EurekAlert Press Statement that hemoglobin might reflect broader physical vulnerability rather than directly cause dementia.
The relationship could even work in reverse: early, undiagnosed dementia might influence nutrition, weight, frailty or anemia.
This Link Has Been Spotted Before
A Dutch team saw a similar pattern years ago, then went looking in brain scans.
A 2019 study in Neurology followed 12,305 initially dementia-free people for about 12 years. Compared with the middle hemoglobin group, those in the lowest group had a 29% higher dementia risk, while those in the highest had a 20% higher risk.
The researchers also examined brain scans from participants without dementia.
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At both ends of the hemoglobin range, they found more white-matter lesions and weaker connections between brain regions. Anemia was also associated with more cerebral microbleeds.
Those scans offered another piece of the puzzle, though they couldn’t prove abnormal hemoglobin caused the changes.
The Korean study builds on that work with a much larger population and separate findings for dementia type and sex.
Another question is why hemoglobin might be low. Anemia can accompany inflammation or bone-marrow disorders, while iron and B vitamins may play a role. The Dutch researchers didn’t measure those nutrients, leaving another question open.
A 2026 Study Adds Another Twist
Anemia and Alzheimer’s-related blood markers may be telling overlapping stories.
Research reported in April followed 2,282 dementia-free Swedish adults aged 60 and older. Anemia was associated with elevated levels of certain Alzheimer’s-related and brain-injury biomarkers, as well as a 66% higher dementia risk.
People who had both anemia and elevated biomarkers faced the highest risk.
That combination raises questions about how doctors should interpret biomarker results when anemia is also present. However, the findings don’t establish anemia as a sign of Alzheimer’s, nor do they show that treating it prevents dementia.
Interestingly, the sex-related findings differed from the Korean study. In Sweden, anemia appeared more strongly associated with dementia risk among men, although researchers cautioned against drawing firm conclusions from those differences.
The studies involved different age groups and blood measurements. For now, neither explains why the patterns diverged.
Why Iron Pills Aren’t the Takeaway
The obvious next step is the one the lead researcher warns against.
Kim was explicit about what the findings should not encourage:
“We want to emphasise that the findings should not be interpreted as advice to take iron supplements, to raise haemoglobin levels, or to lower high haemoglobin levels in order to prevent dementia. An abnormal haemoglobin result should instead be discussed with a doctor, because it may point to underlying health issues that deserve attention,” he said in the Press release.
A separate Australian trial reminds us that changing a biological marker doesn’t necessarily improve the outcome researchers hope to influence.
Across nine sites, 81 people with amyloid-confirmed mild cognitive impairment or early Alzheimer’s received either an iron-removing drug called deferiprone or a placebo.
Deferiprone lowered hippocampal iron levels. Yet over 12 months, participants taking the drug experienced a faster decline than those receiving placebo, particularly in executive function.
Importantly, the trial examined brain iron, not blood hemoglobin. It was also a small treatment study, not an investigation of everyday iron supplements, and cannot establish whether iron generally helps or harms.
Where the Research Goes From Here
The biggest open question is what, if anything, helps.
Despite the growing evidence linking hemoglobin and dementia, none of these studies tested whether raising low hemoglobin or reducing high hemoglobin changes someone’s chances of developing the condition.
Researchers studying brain health have identified midlife as a key period when medical and lifestyle changes may influence later dementia risk. That makes the Korean study particularly interesting, since participants were already 40 or older when their hemoglobin levels were measured.
For now, an unusual hemoglobin result is a reason to talk with a doctor, not a reason to adjust the number yourself. Scientists still need to determine what the relationship means and whether any intervention can change the outcome.
Do you ask your doctor about every number on your lab results, or only the ones that get flagged?
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