Programmed cell death (PCD)

That's a good thing. All you have to do is look in the mirror after a certain age to realize that old cells don't function like young ones. Eliminating old cells in an orderly fashion (and this is done by voluntary cellular suicide) prevents the buildup of abnormal cells whose DNA is mutating in an unfortunate sort of way after years of attacks by roving bands of free radicals.

Population studies suggest that those in the populace who are physically active have a lower risk of colon cancer. Dr. Kristin Campbell and colleagues in Seattle set out to determine if regular exercise encouraged old colon cells to check out in a programmed sort of way.

Nearly 200 men and women were randomly assigned to slouch on in their usual low-activity sort of way or join in a fun aerobic exercise program for one hour on six days each week over the course of a year. Colon tissue samples were collected from all before and after the study period (whoops--fun's over!).

The analyzed samples indicated that exercise increased PCD in the bowels of men but not in women. Campbell was unclear why women's colonic linings were uninterested in the effects of exercise. With regards to the suicidal cells of men, she noted: "We are interested that we saw changes--now we have to figure out why."