You've probably had a routine blood test at some point. Most people never think about the numbers once their doctor says everything looks fine. One of those numbers may say more about long-term brain health than it seems.
A large Korean study found that unusually low and unusually high hemoglobin levels are both linked to a higher risk of dementia years later. It was published in October 2026 in JAMA Network Open.
Hemoglobin is the protein in red blood cells that carries oxygen from your lungs to the rest of your body, including the brain.
Researchers tracked 316,542 Korean adults aged 40 and over for up to 15 years. People in the lowest fifth for hemoglobin were about 16 percent more likely to develop any form of dementia. Those in the highest fifth also faced an elevated risk, producing a U-shaped curve.
Also read: A daily avocado and a cup of mango may do one thing for your heart
Both low and high levels pointed to higher risk
The pattern looked different depending on the type of dementia. For Alzheimer's disease, the lowest hemoglobin levels stood out, with a 14 percent higher risk than the reference group.
For vascular dementia, which is caused by reduced blood flow in the brain, both ends of the scale mattered. The link was stronger in women than in men.
The lead researcher, Hyun Soo Kim, assistant professor at Dong-A University College of Medicine in Busan, told news-medical.net that the study cannot prove hemoglobin causes dementia.
The number may instead act as a visible marker of wider physical vulnerability that matters for brain health.
Also read: One cup of oatmeal a day: what it actually does to your cholesterol
Why hemoglobin may reflect how your brain is doing
The brain is one of the hungriest organs in the body for oxygen. When hemoglobin runs low, less oxygen reaches brain tissue, which can leave cells more exposed to damage over time.
Abnormal values can also reflect other problems. Low readings may point to iron or vitamin B12 deficiency, chronic kidney disease, inflammation, or heavy menstrual bleeding.
High readings can be linked to dehydration, chronic lung disease, or long-term smoking. Any of those routes can affect the brain in their own way.
What a normal hemoglobin number looks like
According to the Cleveland Clinic, the typical range for adult men is 14.0 to 17.5 grams per deciliter. For adult women it is 12.3 to 15.3 g/dL. The exact cutoff can vary slightly by laboratory, by age, and in pregnancy.
Also read: Your leg pain when walking could signal this common artery disease
Kim cautioned that the results are not a reason to take iron supplements or try to adjust hemoglobin on your own. An unusual reading should prompt a conversation with a doctor about what might be behind the number.
Many people shrug off a low reading as feeling tired. The 8 warning signs of anemia most people dismiss as just being tired are worth knowing, because low hemoglobin can quietly point to something treatable.
Caveats worth keeping in mind
The study is observational. It can describe a pattern but not prove cause and effect. Early, undiagnosed dementia can itself affect appetite and nutrition, which may lower hemoglobin and blur the picture.
The findings also come from a single national cohort and need to be tested in other populations. Hemoglobin is just one of many factors tied to long-term dementia risk.
Also read: How eating pistachios every day may affect your cholesterol and heart
If you have had a complete blood count in the past year or two, your hemoglobin result is on file. Ask your doctor what the number was and whether it sits comfortably in the normal range for your age and sex.
Also read: How long should a nap be? Here is what the research actually says
This article is made and published by Mie Hermansen, who may have used AI in the preparation.