Even mild anemia -- low levels of hemoglobin in the blood -- may raise a person's odds for Alzheimer's disease and other types of dementia, a new study finds.
The same Dutch research also found a correlation between heightened dementia risk and high blood levels of hemoglobin.
"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," noted study lead author M. Arfan Ikram, of Erasmus Medical Center in Rotterdam, the Netherlands.
Hemoglobin is the protein in red blood cells that transports oxygen.
The new study included more than 12,000 people averaging 65 years of age. None of the participants had dementia at the beginning of the research.
Hemoglobin levels were measured at the start of the study and 6% of the participants were found to have anemia.
The participants' health was then tracked for an average of 12 years. During that time, 1,520 developed dementia, including 1,194 who were diagnosed with Alzheimer's disease, according to the report published online July 31 in Neurology.
The study was not designed to prove cause and effect. However, the research showed that people with anemia were 41% more likely to develop Alzheimer's disease and 34% more likely to develop any type of dementia than those without anemia, the team reported.
In another finding, people with high levels of hemoglobin were also more likely to develop dementia. Those with the highest levels were 20% more likely to develop dementia than those with levels in the middle.
Those with the lowest hemoglobin levels were 29% more likely to develop dementia than those with levels in the middle, the research found.
In a journal news release, Ikram added that the findings could be significant, given that "the prevalence of dementia is expected to increase threefold over the next decades, with the largest increases predicted in the countries where the anemia rate is the highest."
The question of how hemoglobin levels affect dementia risk is still unclear, however.
"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," Ikram explained.
Dr. Satjit Bhusri is a cardiologist at Lenox Hill Hospital in New York City. Looking over the findings, he stressed that hemoglobin's role as an oxygen transporter to the brain might be key.
"Any quick or slow loss of oxygen will lead to a cognitive decline and manifest as dementia," he noted. Conversely, Bhusri said, "elevated hemoglobin is a reaction to some underlying disease. That disease is forcing the body to produce more hemoglobin. This can result in an increase in thickness of blood and poor flow to the brain."
Another expert believes the findings should serve as a reminder to doctors to pay attention to even mild anemia when it occurs.
"I think that physicians should not write off mild anemia in any age group, because it clearly is associated with brain dysfunction over time," said Dr. Guy Mintz. He directs cardiovascular health at Northwell Health's Sandra Atlas Bass Heart Hospital in Manhasset, N.Y.
Mintz also noted that many of the participants in the study were still in their 60s and 70s, so "we are not looking at an elderly, frail group of patients."
As for people with elevated levels of hemoglobin, he believes that in many instances this happened in response to the smoking habit.
So, the link between hemoglobin levels and dementia "can be another motivational tool to get these patients to stop smoking," Mintz said.
The U.S. National Heart, Lung, and Blood Institute has more on anemia.