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(Reuters Health) - Among people in their 70s, anemia may flag an increased risk of developing dementia later in life, according to a new study.

Researchers following more than 2,500 U.S. adults in their 70s for over a decade found that those who started out with anemia were 65 percent more likely to develop dementia by the end of the study period.

"Anemia is common in the elderly and occurs in up to 23 percent of adults ages 65 and older," said senior author Dr. Kristina Yaffe of the University of California, San Francisco.

People with anemia lack enough healthy red blood cells to carry oxygen throughout the body.

Fewer healthy red blood cells could mean less oxygen travelling to the brain and may result in cognitive decline, she said.

Several conditions, including kidney disease and nutritional deficiencies, can cause anemia.

Previous studies have found an association between anemia and dementia, but they had not followed anemic adults over time to see if they developed cognitive problems, as the current study did, Yaffe told Reuters Health.

She and her coauthors used medical records to follow 2,552 people between the ages of 70 and 79 at the beginning of the study period. They were tested for anemia early in the study and given memory and thinking tests over a total of 11 years.

At the start of the study, 393 participants had anemia. And at the end of the study, 445, or about 18 percent of participants, had developed dementia, based on records of their hospital visits, prescribed dementia medication use or a significant downward change on the memory and thinking tests.

Of the roughly 400 men and women who were anemic at the start, 23 percent developed dementia, compared to 17 percent of the 2,000 others who were not anemic, according to the results published in the journal Neurology.

That six percent difference is a large change in risk on a population level, Yaffe said.

"I think doctors should be aware of this important connection especially as both anemia and dementia are common with aging," she said.

The increased risk for dementia linked to anemia did not change based on race or gender.

Despite the association, the study does not prove that anemia causes dementia, cautioned Dr. Ruth Peters, who researches risk factors for dementia at Imperial College London and was not involved in the new study.

"There are many risk factors that are associated with dementia and these kinds of studies are very useful in identifying and clarifying these," she told Reuters Health by email. "Each individual will have their own mosaic of risk factors."

It is possible that a third influence, like chronic kidney disease, caused both anemia and dementia in the participants with both conditions, but the authors tried to rule that out, Yaffe said.

Low iron levels, which are one cause of anemia, can cause heart problems for older people, so doctors usually check iron and recommend getting more of it from foods like spinach or over the counter vitamins if levels are low, she said.

"However, a third of the time, doctors cannot find a common cause for the lower hemoglobin levels (anemia) in older adults," said Dr. Raj Shah of Rush University Medical Center in Chicago.

Anemia can also result from poor nutrition, bleeding disorders or cancer, among other things, said Shah, who studies cognitive decline in older people but was not involved in the study.

"We still have to understand what is the mechanism by which low hemoglobin is associated with cognitive decline and risk of developing dementia in older persons," Shah told Reuters Health.

Future research should investigate whether correcting anemia also improves cognitive health, Yaffe said.

SOURCE: bit.ly/a55XCO Neurology, online July 31, 2013.