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Anemia linked to increase risk of Dementia

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There is no single test to determine if someone has dementia. The harsh reality is that at this point, it can only be conclusively diagnosed during an autopsy.

So for now doctors rely on physical exams, lab work and cognitive indicators to diagnose dementia with a high degree of certainty while a patient is still alive.

Anemia may be one sign someone has an increased risk of developing dementia, according to a new study published in Neurology, the medical journal of the American Academy of Neurology.

“I’ve been studying Alzheimer’s for a long time,” says study author Dr. Kristine Yaffe, of the University of California – San Francisco. “In particular, I’m interested in things you can modify: cardiovascular disease, sleep, physical activity. We’ve done a number of studies looking at how different chronic diseases of the body effect aging. We started looking into the issue of anemia… after seeing rudimentary studies that linked it to dementia.”

The basics

Anemia is a condition in which your red blood cells don’t carry enough oxygen to the rest of your body. In most cases, a lack of iron causes anemia.

Having anemia may result in extreme fatigue. Loss of blood is the most common cause, resulting in short- or long-term symptoms, which can range from mild to severe.

“Anemia is common in the elderly and occurs in up to 23% of adults ages 65 and older,” says Yaffe. “The condition has also been linked in studies to an increased risk of early death.”

The study

The study followed approximately 2,500 participants who were in their 70s when the data collection began in 1997. They were initially tested for anemia and cognitive function, and underwent subsequent testing over the next decade.

The researchers found that people who had anemia at the beginning of the study had a 41% higher risk of developing dementia than those who were not anemic. The link remained after considering other factors, such as age, race, sex and education.

“There are several explanations for why anemia may be linked to dementia,” says Yaffe. “For example, anemia may be a marker for poor health in general, or low oxygen levels resulting from anemia may play a role in the connection. Reductions in oxygen to the brain have been shown to reduce memory and thinking abilities and may contribute to damage to neurons.”

“The biggest caution in a study like this is over-interpreting it,” says Dr. David Knopman, a neurology consultant at the Mayo Clinic (who served as the handling editor for the publication of this study). “This study does not – and was not intended to – show a causality between anemia and dementia. All it does is show an association.”

The breakdown

The study’s authors concede that “the mechanisms linking anemia to… dementia are not clearly understood” but discussed four hypotheses that had previously been proposed:

1. Chronic brain hypoxia (not getting enough oxygen) associated with anemia may contribute to risk of dementia. Anemia has been associated with the progression of white matter disease in older adults with high blood pressure.

2. Anemia due to chronic kidney disease may be linked to dementia. Erythropoietin receptors, which regulate red blood cell production, seem to have a protective effect on the brain – at least in animal models. Kidney disease or failure is known to lower erythropoietin levels.

3. Anemia due to deficiency of micronutrients – such as iron and vitamin B12 – may also be associated with cognitive impairment and dementia. Deficiency of iron, because it plays an important role in oxygen transport and storage in the brain, may lead to cerebral hypoxia and cognitive decline.

4. It is also possible that anemia is a marker of poor health. Other studies have demonstrated that dementia is often associated with a range of health-related outcomes, or there may be another latent variable associated with both anemia and dementia that is driving the association.

“If I had to vote, I would vote on the fourth one: a marker of poor health,” says Knopman, “but I ultimately can’t prove that. The one thing that links these non-traditional risk factors may be health behavior. The extent to which people are attentive to their health care, generally, seems like the easiest explanation to me.”

Next, Yaffe hopes to investigate the underlying mechanism linking anemia and dementia.

“I have a feeling it’s probably the oxygen story (the lack of oxygen in the brain),” she says. “It’d be important to find out if you treat anemia, does that reduce your likelihood of developing dementia? Obviously, that’s not ethical, because you’d want to treat everyone. But there’s got to be a back-door way to get at that question.”