Too much of a good thing?

The key for men to make it to 85 without relying on someone else to bathe, feed and dress them is to stay trim and active, according to a new study published in the Journal of the American Medical Association.

There are other factors — including not smoking, easing up on the booze, having a strong grip and being married — but it's the exercise aspect that interests me.

Is it a case of the more you exercise the better your odds? Sort of like my grandmother's attitude to diet foods back in the 1960s. She figured if it said "diet" on the label, the more you ate, the more weight you would lose. Grandma didn't exactly have an hourglass figure. Then again, I haven't met too many Greek grandmothers who do.

Still, she made it to almost 100 — without exercising.

I've picked the exercise route, partially because I am very much like my father, who was morbidly obese when a heart attack felled him at age 66. I've been working pretty hard to keep my latent obesity at bay. I'll appease it with the odd big bag of barbecue potato chips — and then run 10 miles the next day to wipe out most of those calories.

People tend to believe that if you exercise regularly, you're less likely to get sick than if you spend your days on the couch watching TV. And there are studies that back that up.

The key is "moderate" exercise. Going overboard can actually suppress the immune system and make you more susceptible to picking up colds and other nasty viruses.

The anecdotal evidence is there. Among the group of people I run with on Sunday mornings, there are bound to be a couple felled by a cold or sinus infection the week after a marathon.

I had gone illness-free for a good two years, until last January. One evening, I noticed a slight wheezing when I was out for an easy run. Within a week, I was knocked flat by the worst bronchial infection I've ever had.

Felt so sick, I even picked out the spot on one of my regular running routes where I wanted the memorial tree planted.

Some researchers suggest that extreme exercisers may be putting themselves at an even greater risk. If you exercise for more than 90 minutes, they say, your immune system pays the price as your body seeks ways to keep going.

One researcher is trying to determine whether there's a link between over-exercising and cancer. A former director of the Western States 100-mile race noticed that a disturbing number of people he knew who competed in the race had developed some form of cancer. The theory is way too much exercise may cause changes to the structure of your cells, opening the door to the mutations that could lead to cancer.

People who like to run marathons or compete in triathalons tend not to understand the definition of the word moderate.

Fortunately, I do. It's running 110 K a week or less.

Yet another study will give people who train for and compete in marathons and triathalons cause for concern. A team of researchers at the Medical University in Graz, Austria has found that marathon runners face an increased risk of developing skin cancer — mainly due to longer exposure to the sun. But they haven't ruled out the effects of intense training on the immune system.

The highest risk was for people who trained more than a moderate 70 kilometres a week. The researchers — all avid runners — advise outdoor exercisers to use sunscreen and to do as much of their training as possible when the risk from the sun is lowest (early mornings or evenings). They found a little more than half the people in their study used sunscreen regularly.