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Here's still another really good reason we shouldn't give "people food" to dogs. One of the sweeteners used in sugar-free gum, candy, baked goods and toothpaste can make dogs sick and could even kill them.

Xylitol "is a naturally occurring product, but it may have far-reaching negative health effect on dogs," according to a clinical report in the Oct. 1 edition of the Journal of American Veterinary Medical Association.

"Not all things that are natural are safe," said veterinarian Sharon Gwaltney-Brant, who co-authored the report with veterinarian Eric K. Dunayer. "There are plenty of things in the environment that are toxic to pets."

Not all pets become ill after eating xylitol, Dr. Gwaltney-Brant said. But she suggests that people who own pets, especially dogs, should be aware of the potential dangers.

The two veterinarians are staff members at the Animal Poison Control Center of the American Society for the Prevention of Cruelty to Animals. They studied eight dogs treated between 2003 and 2005 after eating products containing xylitol. All eight dogs became ill. Three survived. Five dogs died or had to be euthanized because of liver failure "possibly stemming from xylitol ingestion."

Three other dogs examined after the study died or had to be euthanized because of liver failure.

"The number of xylitol-related pet poisonings is on the rise," according to Dr. Gwaltney-Brant, "partly because of increased awareness, but more so because xylitol is being used in more products.

The incidence of reported xylitol poisoning climbed from 70 in 2004 to 170 in 2005. As of August, 2006, the Poison Control Center reported 114 cases of xylitol poisoning.

The sweetener does not seem to pose a problem for people, Dr. Gwaltney-Brant says in a news release from the AVMA. "People only absorb a certain percentage of it. The body doesn't even notice it. However, in dogs, xylitol triggers significant insulin release, which drops the blood sugar. It is definitely a species difference. People aren't in danger from sugar-free gum. Dogs are."

There is no information on whether severe xylitol poisoning has occurred in cats, she said.

One of the dogs in the study ate four large, chocolate-frosted muffins that contained xylitol. The dog had to be euthanized.

A 22-pound dog that consumes one gram of xylitol should be treated, Dr. Gwaltney-Brant said. "That doesn't take very many pieces of gum."

If your dog gets into goodies that contain sugar substitutes, the dog's blood sugar levels should be checked as a precaution, she suggests.

Sweeteners have been linked to low blood sugar in dogs, but findings of liver failure are new, the report says.

Top dogs

Labrador retrievers are still No. 1 on the annual registration list compiled by the American Kennel Club. Labs have held on to the top spot since 1991.

The tiny Yorkshire terrier has knocked Golden retrievers out of the No. 2 spot.

The rest of the top 10: German shepherds are third, golden retrievers are fourth, beagles are fifth, dachshunds are sixth, boxers are seventh, poodles are eighth, Shih Tzus are ninth and miniature schnauzers are 10th.

Breed popularity varies, from city to city, and the AKC has been releasing the top 10 lists for various cities.

Labs are No. 1 in Pittsburgh, but other local rankings are a bit different from the national list. In Pittsburgh, German shepherd dogs are second, golden retrievers are third, beagles are fourth, boxers are fifth, Yorkshire terriers are sixth, Shih Tzus are seventh, dachshunds are eighth, pugs are ninth and Rottweillers are 10th.

Go to www.akc.org to see all of the registration figures on the AKC Web site.

Registration figures, in recent years, have indicated that more people are choosing smaller breeds.

The American Kennel Club registers 155 dog breeds. Which dogs are at the bottom? Here they are: 145, Sussex spaniel; 146, Skye terrier; 147, Finnish spitz; 148, Komondorok; 149, Sealyham terrier; 150, Canaan dog; 151, American foxhound; 152, otterhound; 153, Glen of Imaal terrier; 154, harrier; 155, English foxhound.