Hemoglobin is measured in almost every routine blood count, which makes the link between hemoglobin and dementia worth a closer look. A Korean study that followed 316,542 adults for up to 15 years found that people with the lowest hemoglobin levels developed dementia more often than people in the reference group, and that the very highest levels were also tied to a small increase. The work was published in the Journal of Alzheimer’s Disease in 2026 and drew new press coverage in early October. It describes an association, not a cause. Here is what the researchers measured, what the results cannot tell you, and how to read your own number calmly.
What the hemoglobin and dementia study found
The team used a national health screening cohort. Adults aged 40 and older were screened in 2004 and 2005, then tracked through insurance records until 2019 to see who received a dementia diagnosis. Because normal hemoglobin differs between men and women, participants were sorted into five equal groups (quintiles) separately for each sex. The group with the lowest dementia rate, the fourth quintile, served as the reference.
Low and high levels both stood out
Compared with the reference group, people in the lowest fifth had a higher risk of all-cause dementia, and people in the highest fifth had a smaller but still measurable increase. The pattern was not identical for each type of dementia, as the table shows.
| Hemoglobin group | All-cause dementia | 阿茲海默症 | 血管性失智症 |
|---|---|---|---|
| Lowest 20% | About 16% higher relative risk | About 14% higher | About 19% higher |
| Reference group (fourth fifth) | 參考資料 | 參考資料 | 參考資料 |
| Highest 20% | About 7% higher | No clear increase | About 18% higher |
The association was clearer and more consistent in women than in men. The percentages above come from press coverage of the study, and the pattern (Alzheimer’s risk rising only at lower levels, vascular dementia at both extremes) matches the published abstract.
What “16% higher” really means
These figures are relative risks over many years of follow-up. A 16% relative increase applied to a small baseline chance remains a small absolute change for any one person. The study tells you that the groups differed on average, not that a given hemoglobin value predicts dementia in you.
Why hemoglobin and dementia could be connected
Hemoglobin is the protein in red blood cells that carries oxygen, and the brain depends on a steady supply. Researchers have proposed several explanations, none proven. Low oxygen delivery or iron shortage could stress brain cells over time. Chronic illness and inflammation can lower hemoglobin and also affect brain health. High values may reflect other conditions, such as lung disease, smoking or dehydration, and the study cannot say which applies.
Reverse causation is also possible. Early, undiagnosed dementia can change appetite, weight and nutrition years before a diagnosis, and that could lower hemoglobin. In that scenario, a low value is a sign of what is happening rather than a trigger.
這項研究無法說明的事
The design is observational, so it cannot prove that low or high hemoglobin causes dementia. Hemoglobin was taken at one screening visit in 2004 and 2005, the population was Korean, and the authors call for confirmation in more diverse groups. The abstract suggests that correcting anemia may help, while press coverage quotes the researchers advising against iron supplements or attempts to change hemoglobin purely to prevent dementia. No trial has shown that raising or lowering hemoglobin prevents dementia. A confirmed anemia deserves a proper work-up for its own sake, supervised by a doctor.
最新科學進展
According to PubMed, several 2026 papers look at the same question from different angles, and together they point to a link that is real in the data but not fully explained.
A Swedish study of older adults, published in JAMA Network Open, found that people with anemia had higher levels of Alzheimer-related blood markers and developed dementia more often over the years. Risk was highest when low hemoglobin and raised markers appeared together (DOI). What this changes for you: if a doctor orders an Alzheimer’s blood test, your hemoglobin and iron status help interpret it.
A separate Korean study in Scientific Reports followed adults over 60 with repeated check-ups and found that persistent anemia was linked to more dementia, more strongly for Alzheimer’s than vascular dementia, and more so as anemia became more severe. The effect looked larger in men, which differs from the women-focused pattern above, so sex differences are not settled (DOI).
A 2026 review in Frontiers in Nutrition argues that anemia, iron deficiency and functional iron deficiency are distinct profiles, that no complete causal chain has been shown in humans, and that a complete blood count with iron studies, read in context, is more useful than looking at hemoglobin alone (DOI). An accompanying commentary in JAMA Network Open describes hemoglobin as the “new face of a familiar protein” in dementia prevention research (DOI).
How to read your own hemoglobin result
Use the reference range printed on your lab report, because limits vary by lab, age and sex. In the studies above, anemia was defined as hemoglobin below 13 g/dL in men and below 12 g/dL in women. To see how labs frame every possible result, read our full hemoglobin guide.
| 您的檢驗結果 | 通常代表的意義 | 合理的下一步 |
|---|---|---|
| Inside your lab’s range | No anemia, no action needed for dementia | 一般追蹤 |
| 低於參考範圍 | Anemia from iron, B12 or folate shortage, blood loss, kidney disease or inflammation | Repeat the test and look for the cause with your doctor |
| 高於正常範圍 | Dehydration, smoking, lung or bone marrow conditions, or a high altitude effect | Repeat after good hydration and ask for a medical review |
When hemoglobin is low, doctors usually look at iron stores next. To understand the follow-up tests, read 低鐵蛋白指南. Then review the iron studies panel explained.
何時應與醫師討論
A hemoglobin value is not a dementia test, but it is a reason to look further in some situations. Book a visit if you notice any of the following.
- Persistent fatigue, shortness of breath, pallor, dizziness or palpitations, which are common signs of anemia.
- A hemoglobin result outside the range on two separate blood tests.
- New memory or thinking changes, noticed by you or by people close to you. To learn the early signs, read our dementia overview.
- Heavy periods, black stools or other signs of blood loss alongside a low result.
If you are worried about dementia itself, ask your doctor about the p-tau217 blood test. It is a more specific marker than hemoglobin. For prevention, steps with stronger evidence than any hemoglobin target are covered in our guide to reducing dementia risk.
詞彙表
- 血紅素: the iron-containing protein in red blood cells that carries oxygen.
- 貧血: a condition in which red blood cells or hemoglobin fall below normal.
- Quintile: one of five equal-sized groups used to compare people from the lowest to the highest values.
- 風險比: a measure of how much more (or less) often an event occurs in one group than in another over time.
- 血管性失智症: dementia caused by reduced blood flow to the brain.
常見問題
Does low hemoglobin cause dementia?
No study has shown that. Low hemoglobin is associated with a higher chance of a later dementia diagnosis, but the cause may be anemia itself, an underlying illness, or early disease changing nutrition.
Can anemia increase dementia risk?
Several large cohorts report a higher dementia risk in people with persistent anemia, especially when it is more severe. These are associations, and treating anemia has not been proven to prevent dementia.
What hemoglobin level is considered low?
Many labs use below 13 g/dL for men and below 12 g/dL for non-pregnant women, but your report’s own reference range applies.
Can high hemoglobin also raise dementia risk?
In the Korean cohort, the highest group showed a small increase, mainly for vascular dementia. It may reflect other conditions and needs confirmation.
Should I take iron to protect my brain?
No. Take iron only if a doctor confirms a deficiency, because too much iron can be harmful and the study does not support supplements as prevention.
參考資料
- Mayo Clinic: Anemia, symptoms and causes
- World Health Organization: Anaemia fact sheet
- MedlinePlus: Anemia
- MedlinePlus: Dementia
- Song et al., The association between hemoglobin level and risk of developing dementia, Journal of Alzheimer’s Disease, 2026
- Kang et al., Anemia and risk of dementia in the general population, Scientific Reports, 2026
- Valletta et al., Anemia and blood biomarkers of Alzheimer disease in dementia development, JAMA Network Open, 2026
- Li et al., Anemia, iron deficiency, and blood biomarkers for Alzheimer disease, Frontiers in Nutrition, 2026
- Wolters, Hemoglobin and anemia in dementia prevention, JAMA Network Open, 2026
其他文章
- 血紅素數值：解讀您的血液檢查結果
- 血球容積比檢查：結果說明與正常範圍
- MCV 血液檢查：測量什麼、結果代表什麼
- P-tau217血液檢測：在症狀出現前十年能預測什麼
- 降低失智症風險：WHO 2026年指引有哪些新變化
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