Catching a cold or any other infection could cause more memory loss in people with Alzheimer's disease, a new study suggests.
Alzheimer's is a form of dementia generally diagnosed in some people over 65. While it can result in everything from mood swings to language breakdown and loss of bodily functions, the most familiar hallmark of the disease is memory loss.
At first, the memory lapses are subtle — forgetting a recently learned fact or having difficulty absorbing new information — but they gradually build as the disease progresses so that vocabulary is lost and older memories, previously held intact, slip away.
The biological mechanisms that cause the disease and drive its progression are still not well-understood, but the new research, detailed in the Sept. 8 issue of the journal Neurology, suggests that infections could antagonize the progression.
Delirium vs. dementia
Scientists have long known that people who contract acute infections can experience a severe temporary memory loss, what is known as a delirium, and that Alzheimer's patients are particularly susceptible to deliriums after an illness. But the new work looks at the impact beyond this type of temporary memory loss.
"What this research shows is that even quite mild infections, that aren't bad enough to cause a delirium, can cause a longstanding and permanent loss in memory function that over time could help to drive the progression of the disease from its mild stages to its more severe stages," said study author Clive Holmes of the University of Southampton in the United Kingdom.
The study looked at 222 people with Alzheimer's disease with an average age of 83. Their cognitive abilities and blood were tested at the beginning of the study and then three more times over the course of six months. The caregivers of the patients were asked about any infections or accidental injuries the patients might have had during the study period.
A total of 110 study subjects experienced an infection or injury, and their memory loss occurred at twice the rate of those who didn't become ill.
The researchers suspect that the memory loss is related to a protein related to inflammation that circulates in the blood during an infection.
Protein levels
The potential culprit is called tumor necrosis factor-alpha. The researchers found elevated levels of these proteins in patients who had experienced an infection and then accelerated memory loss.
In addition, study participants who had high levels of the protein in their blood at the beginning of the study — a possible sign of chronic inflammation — had four times the rate of memory loss as those with low levels of the protein at the start of the study. Those who had both high beginning levels and experienced an infection had 10 times the memory loss.
Holmes and his colleagues think that the memory loss might be occurring because the protein sends a signal to the brain that "causes the brain in someone with Alzheimer's disease to respond by causing a large increase in the brain's own inflammatory molecules," he told LiveScience. These increases are much higher than would occur in someone without Alzheimer's and end up causing more brain damage.
Further research is needed to pinpoint the exact mechanism taking place, but it could lead to ways to help prevent increased memory loss by reducing levels of the protein in someone with an infection. And in the meantime, the new research, supported by the Alzheimer's Society, suggests it would at least be prudent to try to reduce the chances of someone with Alzheimer's getting an infection.
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