If you're like 40 percent of Americans, you take some sort of multi-vitamin or nutrient supplement. And if you're like 100 percent of dog owners, your pet's health is of the utmost importance to you. So why not feed dog his very own supplements?

One of the best supplements for dogs (and cats) is cod liver oil, which humans have been ingesting for centuries as a cure-all for everything from acne to indigestion. It has even been credited with helping heart-attack patients recover faster and improving brain function and memory.

There are numerous health benefits in cod liver oil for dogs, too; it has said to relieve arthritis, prevent kidney disease and control allergies. But how?

Aptly named, cod liver oil is extracted from the livers of cod fish. It is remarkably high in Omega-3 fatty acids, as well as vitamins A, E and D. EPA, one type of Omega-3 fatty acid, has been shown to reduce damage to joint cartilage, thereby alleviating arthritis pain. The oil has anti-inflammatory properties, which helps it fight ailments like inflammatory bowel disease and rheumatoid arthritis. Cod liver oil could even make your dog smarter: DHA, another Omega-3 fatty acid found in the oil, has been shown to improve learning and trainability in puppies.

Some pet foods boast Omega-3 fatty acids in their recipe, but that is a deceitful claim. Dry food is highly processed and Omega-3 fatty acids cannot live through the heat necessary to create dry dog food. The food may contain another form of fatty acids, such as flax seed, but note that flax seed oil must be converted internally into EPA and DHA, and many animals lack the enzymes to properly undertake that task.

The best way to administer cod liver oil for dogs is by breaking open a capsule (or part of a capsule, for smaller dogs) and drizzling the contents over your dog's food every day. Don't worry about the taste - its fishy smell and flavor will please almost any dog.

Please note, however, that administering too much cod liver oil can be harmful for your dog. It is rich in vitamins A and D, which can be harmful if taken in large doses; too much vitamin D can even be toxic. Plus, some manufacturing companies do not test as rigorously as they should for chemicals commonly found in fish, such as mercury. Because cod liver oil comes from a fish's liver (which filters out toxins in the fish' body), it could contain high levels of harmful substances.

Also note that, like food, cod liver oil contains calories! Overindulging may throw dog's caloric intake off balance.

For more information about cod liver oil for dogs or to start your pet on a regimen, be sure to consult your veterinarian.