Routine blood test hemoglobin levels may signal future dementia risk

A routine blood test that millions of people already get during annual checkups may hold clues about whether someone will develop dementia years or even decades later. Researchers tracking over 316,000 Korean adults for up to 15 years found that hemoglobin levels—the protein in red blood cells that ferries oxygen through the body—showed a measurable association with dementia risk, a finding presented this week at the European College of Neuropsychopharmacology Congress in Munich and published in the Journal of Alzheimer's Disease.

The study began in 2004 and 2005, when participants aged 40 and older underwent routine national health screening. Researchers then followed their medical records through the end of 2019, watching for new dementia diagnoses. They divided the participants into five groups based on hemoglobin levels, from lowest to highest. The pattern that emerged was striking in its simplicity: people in the bottom fifth for hemoglobin had a 16 percent higher risk of developing dementia of any kind compared to those with the lowest dementia rates. Those in the top fifth—with unusually high hemoglobin—faced a 7 percent elevated risk.

The relationship shifted depending on the type of dementia. For Alzheimer's disease specifically, the increased risk concentrated almost entirely in the lowest hemoglobin group, which showed a 14 percent higher likelihood of developing the disease. Vascular dementia, caused by reduced blood flow to the brain, told a different story: the lowest hemoglobin group had a 19 percent higher risk, but the highest hemoglobin group also showed an 18 percent increased risk, suggesting a U-shaped curve rather than a simple linear relationship. The association appeared more pronounced and consistent in women than in men.

Dr. Hyun Soo Kim, the lead researcher and an assistant professor at Dong-A University College of Medicine in Busan, South Korea, emphasized that the findings do not prove hemoglobin causes dementia. Instead, he framed abnormal hemoglobin levels as a visible marker of broader physical vulnerability that may matter for brain health. Low hemoglobin typically signals anemia, while high hemoglobin can reflect smoking, dehydration, lung disease, heart disease, or other medical conditions—all of which carry their own health implications.

What makes this research potentially significant is its accessibility. Hemoglobin is already measured in standard blood tests performed worldwide. Unlike specialized brain imaging or emerging biomarkers that require expensive equipment or specialized labs, hemoglobin testing is inexpensive, familiar to doctors and patients alike, and often already documented in existing medical records. For researchers and clinicians trying to identify people at higher risk of dementia, a test that is already routine and universally available offers practical advantages.

Kim stressed an important caveat: the study was observational, meaning it can identify associations but cannot prove causation. Early, undiagnosed dementia processes might themselves affect nutrition, body weight, or anemia levels, creating a reverse relationship where the disease influences hemoglobin rather than the other way around. He was explicit that the findings should not prompt people to take iron supplements or attempt to self-correct hemoglobin levels. Instead, any abnormal hemoglobin result warrants a conversation with a doctor, who can investigate what underlying health issue might be driving the abnormality.

Dr. Lindsey Sinclair from the University of Southampton, commenting on the work, noted that evidence increasingly points to physical and brain health being intertwined, with mid-life health changes—whether medical or lifestyle-based—playing a role in reducing later dementia risk. She called for further research to determine whether the hemoglobin-dementia link holds across more diverse populations and what interventions might actually help people with abnormal hemoglobin levels reduce their dementia risk.