Researchers at the University of Utah gave mice a diet of 25% sugar—equivalent to three extra sodas per day in people—and found the males less likely to reproduce or defend their territory. Females had it worse, dying at double their normal rate. Now consider that the National Research Council tells us that this level of added sugar is considered safe in humans.
Why rely on a study of mice? They're considered roughly equivalent to humans in dietary studies because they've had a similar diet to ours for about 10,000 years, and up to 80% of what's toxic to them is toxic to people.