Adults with low levels of hemoglobin and adults with high levels of hemoglobin have an increased risk of developing dementia over 12 years of follow-up, compared with adults with midrange levels, according to a population-based study in the Netherlands.

This U-shaped association “may relate to differences in white matter integrity and cerebral perfusion,” the researchers wrote in Neurology.

M. Arfan Ikram, MD, PhD, professor of epidemiology at Erasmus Medical Center in Rotterdam, the Netherlands Ton Everaers, Erasmus Medical Center

Dr. M. Arfan Ikram

“With around 10% of people over age 65 having anemia in the Americas and Europe and up to 45% in African and southeast Asian countries, these results could have important implications for the burden of dementia,” said study author M. Arfan Ikram, MD, PhD, in a news release. Dr. Ikram is a professor of epidemiology at Erasmus Medical Center in Rotterdam, the Netherlands.

Prior studies have found that low hemoglobin levels are associated with adverse health outcomes, such as coronary heart disease, stroke, and mortality, but data about the relationship between hemoglobin levels and dementia risk have been limited.

A population-based cohort study

To examine the long-term association of hemoglobin levels and anemia with risk of dementia, Dr. Ikram and coauthors analyzed data from the Rotterdam Study, an ongoing population-based cohort study in the Netherlands that started in 1990. Their analysis included data from 12,305 participants without dementia who had serum hemoglobin measured at baseline (mean age, 64.6 years; 57.7% women).

During a mean follow-up of 12.1 years, 1,520 participants developed dementia, 1,194 of whom had Alzheimer’s disease.

“Both low and high hemoglobin levels were associated with increased dementia risk,” the authors wrote. Compared with participants in the middle quintile of hemoglobin levels (8.57-8.99 mmol/L), participants in the lowest quintile (less than 8.11 mmol/L) had a hazard ratio of dementia of 1.29, and participants in the highest quintile (greater than 9.40 mmol/L) had an HR of 1.20.

About 6% of the participants had anemia – that is, a hemoglobin level of less than 8.1 mmol/L for men and less than 7.5 mmol/L for women. Anemia was associated with a 34% increased risk of dementia and a 41% increased risk of Alzheimer’s disease.

Of the 745 people with anemia, 128 developed dementia, compared with 1,392 of the 11,560 people who did not have anemia (17% vs. 12%).

A U-shaped association

The researchers also examined hemoglobin in relation to vascular brain disease, structural connectivity, and global cerebral perfusion among 5,267 participants without dementia who had brain MRI. White matter hyperintensity volume and hemoglobin had a U-shaped association, similar to that for dementia and hemoglobin. In addition, hemoglobin inversely correlated to cerebral perfusion.

The results remained consistent after adjustment for factors such as smoking, high blood pressure, high cholesterol, and alcohol use.

A limitation of the study is that the participants lived in the Netherlands and were primarily of European descent, so the results may not apply to other populations, the authors wrote.

Dr. Ikram noted that the study does not prove that low or high hemoglobin levels cause dementia. “More research is needed to determine whether hemoglobin levels play a direct role in this increased risk or whether these associations can be explained by underlying issues or other vascular or metabolic changes.”

The study was supported by the Netherlands Cardiovascular Research Initiative; Erasmus Medical Centre; Erasmus University Rotterdam; Netherlands Organization for Scientific Research; Netherlands Organization for Health Research and Development; Research Institute for Diseases in the Elderly; Netherlands Genomic Initiative; Dutch Ministry of Education, Culture, and Science; Dutch Ministry of Health, Welfare, and Sports; European Commission; Municipality of Rotterdam; Netherlands Consortium for Healthy Aging; and Dutch Heart Foundation. The authors reported no relevant disclosures.

SOURCE: Ikram MA et al. Neurology. 2019 Jul 31. doi: 10.1212/WNL.0000000000008003.