(CNN) -- Kim Stevens has a problem that affects tens of millions of Americans. If left untreated, it could lead to the death of someone she loves, someone who's part of the family.

Stevens' dog Dodger, a black and gray mixed breed, is obese. According to a new study, he's emblematic of a growing problem.

The majority of adult dogs and cats in U.S. homes are overweight or obese, and the problem has gotten worse over the past year, according to the Association for Pet Obesity Prevention. Fifty-three percent of adult dogs and 55% of cats were classified as overweight or obese by their veterinarians.

"I didn't notice the weight creeping on -- it was like all of a sudden he was just this fat dog," Stevens said as she and Dodger visited Atlanta's Centennial Olympic Park.

"His weight is about 82 pounds right now, and he should be 62 pounds." That means he needs to lose about a quarter of his weight -- equivalent to a 200-pound person needing to lose 50 pounds.

The reason is pretty simple: "Too much food and not enough exercise," Stevens said.

The Association for Pet Obesity Prevention report shows not only that more pets are overweight, but also that those with the problem "are getting fatter," said Ernie Ward, the group's founder.

The annual study, to be released next week and given in advance to CNN, found that 25% of cats and just more than 21% of dogs are obese. Both those figures are up slightly from 2010.

About 41 million dogs are overweight.

About 41 million dogs and 47 million cats are overweight or obese, the study found.

A long list of health dangers comes with the excess weight. "It's not a matter of if, it's when" serious complications will strike, said Ward.

These can include high blood pressure, "crippling arthritis," diabetes and some cancers. "Their life is shortened by two or 2