Could having hay fever be good for your memory?

For anyone who’s spent much of the summer struggling with itchy, puffy eyes and a runny nose, it’s hard to believe that hay fever has anything to recommend it. But would you feel better if it could help your memory?

researchers at the Institute of Molecular regenerative Medicine in Salzburg, Austria, have found that an allergy to grass pollen could have this beneficial effect.

In an experiment published in the journal Frontiers in Cellular Science, researchers exposed mice to Timothy grass pollen (one of the main hay fever triggers in the UK) to induce an allergic reaction and then studied the hippocampus area of their brains, which is associated with memory.

The allergic reaction stimulated the growth of new neurons (nerve cells) in the hippocampus. This was significant as the brain contains billions of neurons, which are responsible for communicating signals and forming new memories, but, as we age, the numbers decline.

However, there was a second — and rather unexpected — benefit from the allergic reaction. Instead of activating the immune system within the hippocampus, the allergic reaction suppressed it.

THe researchers think this dampening down of the hippocampus’s immune system, specifically cells called microglia, could be important in slowing down the deterioration of the memory.

The microglia seek out invaders such as bacteria and allergens and destroy them.

But it’s thought that as we get older, these immune cells fire too readily and have an exaggerated response to stimuli. They also become inflamed, contributing to a deterioration of the memory.

‘It’s thought this exaggerated response to stimuli exacerbates the progression of neurodegenerative diseases,’ says Dr Barbara Klein, one of the scientists leading the experiment. ‘our finding that microglia in the hippocampus are deactivated by grass pollen allergy is highly interesting.’

Hay fever is very common: the NHS estimates that more than ten million people in england alone suffer from it. So would these people be less prone to dementia or memory loss? Dr Klein thinks more research is needed — in this experiment, the mice were exposed to the pollen for a short time — only three days. The next step would be to see if the effects last in an allergic response over a longer time frame.

She would also like to see if other allergens, such as foods or house mites, elicit the same reaction.

Finally, research is needed to find out if dampening down the immune system in the hippocampus has any disadvantages.

‘Findings in mice cannot be directly applied to people,’ says Dr Pamela ewan, a consultant allergist at Addenbrooke’s Hospital in Cambridge. But this is not the only intriguing study to suggest allergies might have an unexpected effect.

While an allergic reaction to grass pollen may suppress the immune system in the hippocampus, within the body it has the opposite effect. Here, the immune system goes on red alert. The lungs and respiratory tract become inflamed, resulting in sneezing, a runny nose and itchy throat.

As Good Health reported last week, a study has suggested that this inflammatory response may feed in to a type of seasonal affective disorder (SAD), known as ‘summer SAD’.

While some people develop a winter version of SAD, when a lack of sunlight makes sufferers depressed and lethargic, around 1 per cent of the population gets a similar condition in the summer.

Summer SAD can make you feel anxious and cause difficulty sleeping and is thought to be the result of producing too little of a hormone called melatonin, which makes you sleepy.

APrelIMINAry study published in the Journal of Affective Disorders in 2007 suggests there may be a link between summer SAD and the high prevalence of pollen in spring and summer.

one theory is that people with summer SAD are also affected by hay fever, with the inflammation triggered by the allergic reaction to pollen possibly a factor in their low mood.

Dr Klein believes we are on the brink of finding out more about the immune system, its interplay with allergies and the impact this has on ageing.

She told Good Health: ‘your immune system affects how you age. If an older person in their 70s or 80s is healthy, it’s not just about sport or diet. It’s also about how their immune system copes over their lifetime.

‘People who get a lot of colds, might be at a disadvantage, because their immune system is constantly inflamed. But allergy seems to induce a different response — it seems to have a different impact on brain ageing.’