Unusually high or low hemoglobin levels may indicate an increased risk of dementia, according to the latest research.Low hemoglobin was associated with an increased risk of Alzheimer’s disease, while both high and low levels were linked to a higher risk of vascular dementia.Experts advise that, while hemoglobin levels do not directly cause dementia, they may reflect underlying conditions, such as iron deficiency, chronic kidney disease, and cardiovascular issues.

The aim of the study was to evaluate the potential link between hemoglobin levels and dementia risk among Korean adults. It also examined whether there was a stronger association in men or women.

The researchers analyzed data from 316,542 participants ages 40 years and over who had had a national health screening in 2004 to 2005, then monitored for dementia diagnoses for 15 years, until 2019.

They found that the highest and lowest hemoglobin levels were linked with an increased all-cause dementia risk. Certain groups were also more likely to experience either Alzheimer’s disease or vascular dementia.

In a press release, Hyun Soo Kim, PhD, study author and assistant professor at Dong-A University College of Medicine, Busan, South Korea, spoke about the importance of the research:

“Dementia is one of the fastest-growing health challenges in aging societies, and there are not many treatments and no cure. Identifying simple, accessible markers of future risk could help researchers and clinicians better understand how whole-body health relates to brain health over time.”

The researchers found that the individuals with the highest and lowest hemoglobin levels were most likely to receive a dementia diagnosis later on.

Participants were placed in one of 5 groups, ranging from the lowest hemoglobin levels to the highest.

Individuals in the group with the lowest hemoglobin levels were 16% more likely to develop dementia, while those with the highest hemoglobin levels had a 7% higher risk.

“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,” explained Kim in the press release.

Medical News Today spoke with Dung Trinh, MD, internist, of MemorialCare Medical Group and Chief Medical Officer of Healthy Brain Clinic in Irvine, CA, to find out about the clinical significance of these findings.

“A 16% increase in dementia risk is certainly worth paying attention to, especially given how common low hemoglobin and anemia can be in older adults. However, it’s important to understand that we’re talking about a relative increase in risk, not an absolute 16% increase in someone’s chance of developing dementia,” explained Trinh, who was not involved in the study.

“This study followed more than 316,000 adults in South Korea and found that people with the lowest hemoglobin levels had a 16% higher adjusted hazard of developing dementia compared with those in the reference group. While this increase is relatively modest for any one individual, it could have meaningful implications at the population level,” he added.

“What I find particularly interesting is that hemoglobin is something we routinely measure with a simple blood test. This gives us another potential piece of information about a patient’s overall health and possibly their long-term brain health. However, we cannot conclude from this study that raising hemoglobin levels will prevent dementia.”

The risk of vascular dementia increased in individuals with either the highest or the lowest levels of hemoglobin, an increase of 18% and 19%, respectively.

However, the chance of Alzheimer’s disease only rose in individuals with lower hemoglobin levels, with an increased risk of 14%.

“There are some interesting biological explanations for this finding,” said Trinh.

“Hemoglobin is responsible for carrying oxygen throughout the body, including to the brain. When hemoglobin levels are low, the brain may receive less oxygen, particularly if anemia is significant or prolonged. Chronic reductions in oxygen delivery could potentially contribute to changes in vulnerable brain regions, such as the hippocampus, which plays an important role in memory.”

He explained, “Both low and high hemoglobin levels could potentially contribute to vascular problems through different mechanisms. Low hemoglobin may compromise oxygen delivery, while high hemoglobin can increase blood viscosity and may be associated with a greater risk of blood clots and strokes.”

Trinh added that “[t]hese are plausible explanations, but the study did not directly demonstrate that these mechanisms caused dementia.”

The relationship between hemoglobin levels and dementia risk was stronger among women than men, according to the study findings. Women accounted for 42% of the study population.

Trinh explained that this suggests “that there may be important sex-related differences that deserve further investigation.”

He added that women may experience “low hemoglobin due to menstrual blood loss, especially before menopause.”

Further research could help determine whether women are more likely to develop dementia than men as a result of high or low hemoglobin levels.

There is no evidence to suggest that higher or lower hemoglobin levels directly cause dementia.

As Kim explained in the press release, “[t]he 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.”

MNT asked Trinh whether abnormal hemoglobin levels could indicate an underlying health problem that could also increase the risk of dementia.

“Low hemoglobin can be associated with iron deficiency, vitamin B12 deficiency, chronic kidney disease, inflammation, or other chronic illnesses. Some of these conditions may independently affect cognitive function or overall brain health,” he explained.

“Higher hemoglobin levels can sometimes be associated with dehydration, smoking, chronic low oxygen levels, sleep apnea, or certain blood disorders. Many of these conditions also have implications for cardiovascular health, which we know is closely connected to brain health,” he added.

Trinh concluded, “What I find encouraging about this study is that it reminds us how closely brain health is connected to the rest of the body. We often think about Alzheimer’s disease primarily in terms of memory loss and changes in the brain, but our cardiovascular health, nutrition, metabolism, and overall medical conditions may all influence how our brains age.”

“My message to patients is that protecting your brain starts with taking care of your overall health. Regular physical activity, good nutrition, adequate sleep, controlling blood pressure and diabetes, and staying socially and mentally engaged remain some of the most practical steps we can take to support healthy brain aging.”

– Dung Trinh, MD, in an interview with Medical News Today