Both high and low levels of haemoglobin may be associated with the development of dementia years later, suggests a study.
The study was published in the journal 'Neurology'.
"The prevalence of dementia is expected to increase threefold over the next decades, with the largest increases predicted in the countries where the anaemia rate is the highest," said M. Arfan Ikram, study's author.
The study involved 12,305 people with an average age of 65 who did not have dementia. Participants' haemoglobin levels were measured at the start of the study. Overall, 745, or 6 per cent, of the participants had anaemia.
The participants were followed for an average of 12 years. During that time, 1,520 people developed dementia. Of those, 1,194 had Alzheimer's disease.
The researchers found that people with anaemia were 41 per cent more likely to develop Alzheimer's disease and 34 per cent more likely to develop any type of dementia than those who did not have anaemia. Of the 745 people with anaemia, 128 people developed dementia, compared to 1392 of the 11,560 people who did not have anaemia.
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People with high levels of haemoglobin were also more likely to develop dementia. High levels can also be a sign of a health problem.
The study participants were divided into five groups based on their haemoglobin levels. Compared to the middle group, the group with the highest levels were 20 per cent more likely to develop dementia. Those in the lowest group were 29 per cent more likely to develop dementia than those in the middle group.
The results stayed the same after researchers adjusted for other factors that could affect the risk of dementia, such as smoking, high blood pressure, high cholesterol and alcohol use.
Ikram noted that the study does not prove that low or high haemoglobin levels are a factor in causing dementia; it only shows an association.