Lowered melatonin secretion was an implied factor in the 35 percent increase in colon cancer among night shift nurses, compared with their daytime counterparts. A couple of altered lifestyle factors may contribute, as well: The night shift is often occasion for a sedentary work style, and decreased alertness might even affect daytime activity. Also, there may be the tendency during the night toward eating low-fiber, oily, salty, and sugary snack foods.

Clyde Roggenkamp
Loma Linda, Calif.

Did Eva S. Schernhammer’s research team control for diet? Caffeine? Nicotine?

M. Wood
Waianae, Hawaii

The researchers controlled for such variables and daily hours of sleep .–J. Raloff