Coughs and colds might speed Alzheimer's decline

It may be that infections cause inflammation in the body, which speeds up the damage caused by Alzheimer’s. However, another explanation for the link is that people with worsening Alzheimer’s are more vulnerable to infections.

Researchers are trying to better understand the causes of Alzheimer’s, partly to aid the development of new treatments. One theory is that inflammation plays an important role. Inflammation is the body’s response to illness or injury, and happens because of chemicals produced by the immune system. One of the chemicals that helps to create inflammation is called TNF-alpha.

In a new study, researchers have looked at whether higher levels of TNF-alpha in the blood of people with Alzheimer’s could mean they deteriorate more quickly. Since TNF-alpha is part of the body’s response to infections and injuries, they also looked at whether everyday illnesses, falls, and bruises were linked to worsening Alzheimer’s.

What does the new study say?
Over six months, 275 people with Alzheimer’s took repeated tests that measured memory and the ability to think. They also had blood tests to check levels of TNF-alpha. Their care-givers were asked to record any illnesses or injuries, such as coughs, colds, upset stomachs, urinary tract infections, falls, and bruises. People who had higher TNF-alpha at the start of the study had slightly lower scores on memory and thinking tests after six months. People with low levels had a drop of about 0.8 points, compared with 2.4 points for people with high levels. About half the people in the study had at least one infection or injury. These people were also likely to get poorer test scores. People who hadn’t been ill saw their average score drop by 1.6 points, compared with 3.5 for people who had at least one infection or injury.

Although the researchers did find a bigger drop in test scores for people suffering inflammation, the differences were small. They amount to about 2 points, and the scale ran from 0 to 70. Doctors usually say that there must be a change of about 4 points on this scale before you’d notice a difference in the severity of someone’s Alzheimer’s.

How reliable are the findings?
The study did find a link between infections and worsening Alzheimer’s, but it’s impossible to be sure that these illnesses really caused the decline. It might be that as people become more ill with Alzheimer’s, they’re more vulnerable to infections and injuries. For example, research has shown that people who have Alzheimer’s have a higher risk of falls. It’s also possible that someone struggling to look after themselves might have difficulty with things like regularly washing their hands, which can increase the risk of colds and flu.

Another issue is that infections can make people confused. This could have led to lower scores in the memory tests, rather than worsening Alzheimer’s. The researchers took cases of delirium caused by infection into account, but they might have missed milder cases of confusion.

Where does the study come from?
The study appeared in the journal Neurology, which is published by a company called Lippincott Williams & Wilkin, on behalf of the American Academy of Neurology. The study was supported by the Alzheimer’s Society, a UK charity.

What does this mean for me?
In the long term, drugs that affect the way the immune system creates inflammation might be useful in treating or preventing Alzheimer’s. But this is still a long way off. People with Alzheimer’s can forget about, or lose interest in looking after themselves properly, so helping them attend to basic hygiene might reduce the likelihood of infections. You could also take steps to prevent falls, such as making sure the environment is brightly lit and uncluttered. Some gentle exercise may also help prevent falls.

BMJ Group