You probably think you're doing everything you can to stay healthy. You get lots of sleep, exercise regularly and try to avoid fried foods.

But you may be forgetting one important thing. Relax! Stress has a bigger impact on your health than you might realise, according to research presented yesterday at the annual conference of the American Psychological Association in Boston.

Ohio State University psychologist Janice Kiecolt-Glaser and her partner, Ronald Glaser, an OSU virologist and immunologist, have spent 20-odd years researching how stress affects the immune system, and they have made some startling discoveries.

An easy example comes from their work with caregivers, people who look after chronically ailing spouses or parents (no one would argue that this role is quite stressful).

In one experiment, Kiecolt-Glaser and her colleagues administered flu vaccines to caregivers and control subjects and compared the numbers of antibodiesproteins involved in immune reactionsthat the two groups produced in response.

Only 38 per cent of the caregivers produced what is considered an adequate antibody response compared to 66 per cent of their relaxed counterparts, suggesting that the caregivers' immune systems weren't doing their jobs very well and that the stress of caregiving ultimately put them at an increased risk of infection.

If stress affects immune responses, then it should also affect how well the body heals itself. In one particularly cringe-worthy study, Kiecolt-Glaser and her colleagues afflicted a group of caregivers with small arm wounds using a tool dermatologists use to perform skin biopsies.

The caregivers' wounds took 24 per cent longer to heal than wounds that they had afflicted to non-caregivers.

OK, but what if caregiving isn't an accurate proxy for stress? To explore other stressful situations, Kiecolt-Glaser and colleagues performed another experiment in which they produced tiny lesions in the mouths of, quite appropriately, 11 dental students at two different points in time.

Once was during their summer vacation, when they were relaxed, and once was during the fall, several days before a difficult exam. The lesions done before the exam took from two to eight days longer to heal than the summer wounds. For some subjects, the exam wounds took nearly twice as long to get better. Ouch.

It might seem counterintuitive, but Kiecolt-Glaser believes that stress makes our immune systems less effective because it actually elicits an immune response itself. Stress, she says, causes the body to release pro-inflammatory cytokines, immune factors that initiate responses against infections.

When the body produces these cytokines over long periods of time, for instance, as a result of chronic stressall sorts of bad things can happen. Not only does it hamper our body's ability to fight infection and heal wounds, but chronic inflammation also increases our risk of heart disease, osteoporosis, and autoimmune diseases including type 2 diabetes.

What's more, because regular stress causes a chronic immune response, it can also increase a person's risk for allergies, which occur when the body elicits a chronic immune response against something that's not really dangerous (like pollen).

In her most recent study, announced yesterday, Kiecolt-Glaser found that when people are under lots of stress, for instance, when they are forced to deliver a speech or do difficult math problems on the spot their allergies worsen over the course of the next day.

I admit, this article may not exactly have the intended effect - worrying about the danger of stress is definitely stressful, but take a deep breath. If you ask me, learning a few relaxation techniques sounds like a more appealing illness-prevention strategy than many other alternatives.

(Go ahead and throw away that cod liver oil.) Indeed, the next time you feel guilty about enjoying a lazy Sunday, or taking a day off from work for the heck of it, think again. Your body will thank you for it.

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