Eating too much red meat could raise the risk of Alzheimer's disease by increasing levels of iron in the brain, American researchers claim.
A study of Alzheimer's patients found that iron had begun to accumulate in part of the brain which is generally damaged in the early stages of the disease, but not in a region which tends to be affected much later.
Comparing the results against a separate set of brain scans, they found that iron levels were linked to tissue damage in Alzheimer's patients but not in healthy older people. Although the study did not prove that iron is responsible for the disease, researchers said it "may indeed contribute to the cause".
Lowering the amount of red meat and iron dietary supplements people consume can reduce the amount of iron which builds up in the brain.
Most studies have focused on proteins called tau and beta-amyloid which collect in the brains of sufferers and are thought either to disrupt nerve cells or kill them.
But the new study, by the University of California Los Angeles, suggests that iron accumulation is a third possible contributing factor.
Although iron is essential for cells to function, some researchers believe it can be toxic in high quantities.
The highest iron concentrations in the brain are found in cells which produce myelin, the fatty tissue which coats nerve fibres and allows them to communicate with one another.
The destruction of myelin promotes the build-up of plaques which lead to further deterioration and cell death, the researchers explained. They studied two regions of the brain in 31 Alzheimer's sufferers: the hippocampus, which plays an important role in memory and is usually damaged early in the disease, and the thalamus, which is involved in sensory perception and motor skills, and generally remains healthy until a later stage. Writing in the Journal of Alzheimer's Disease, they reported that unusually high levels of ferritin, a protein which stores iron, were found in the hippocampus of Alzheimer's sufferers, but not in the thalamus.
Professor George Bartzokis, who led the study, said: "The increase in iron is occurring together with the tissue damage. We found that the amount of iron is increased in the hippocampus and is associated with tissue damage in patients with Alzheimer's but not in the healthy older individuals, or in the thalamus.
"So the results suggest that iron accumulation may indeed contribute to the cause of Alzheimer's disease.
"The accumulation of iron in the brain may be influenced by modifying environmental factors, such as how much red meat and iron dietary supplements we consume and, in women, having hysterectomies before menopause."
Dr Marie Janson, of Alzheimer's Research UK, said it was not clear from the study whether the build-up of iron might be a cause or consequence of the disease.