“We did a study on two kinds of supplements people frequently decide to give to their dogs with heart disease,” says Tufts veterinary nutritionist Lisa Freeman, DVM, PhD, DACVN, “and found that six of 13 products did not disintegrate effectively, which suggested that they may not be be absorbed effectively in the gastrointestinal tract.
“Another study, conducted by researchers at the University of Guelph in Ontario, looked at probiotics — both veterinary and human products. In 17 out of 44 supplements — more than one in three — the probiotic organism was either improperly identified or did not even exist.
“People think supplements are regulated as if they were drugs,” Dr. Freeman says. “But they’re not. Drugs must be proven to be safe and effective and made with good quality control before they’re put on the market. Supplement manufacturers don’t have to prove anything. The onus is on the Food and Drug Administration to prove there’s a problem after a supplement comes out in order to remove it from the marketplace. And that’s very unlikely to happen. With the thousands of supplements on the market today, this is an unrealistic task.
“There’s very little evidence for most supplements given to dogs in the first place,” Dr. Freeman comments. Add to that the fact that research has shown that what’s actually in supplements is “all over the board; that dissolvability is really variable, indicating that the pill may not dissolve effectively enough in the gastrointestinal tract to be absorbed; and may not have bioavailability even if absorbed,” she says, and it’s clear that in the majority of cases, dogs and supplements do not mix. The lack of quality control in terms of the amount of so-called active ingredient present can be particularly surprising. The label might say the product contains 500 milligrams, but it could quite conceivably contain 0 milligrams, or 1,000 milligrams. (This is true for supplements intended for people, too.)
Unfortunately, the evidence hasn’t caught up with popular opinion. Although the number of dogs taking dietary supplements is not known, it appears to be growing. “In magazines for pet owners and veterinarians alike,” Dr. Freeman points out, “advertisements for dietary supplements abound.” Owners of sick dogs may be particularly vulnerable to promises of improved health. In one study, almost one in three dogs with heart disease were being administered supplements.
Concern about that trend is heightened by the fact that some supplements have been found to contain contaminants, Dr. Freeman says. Certain fish oils could have mercury, while other supplements have been found to be contaminated with lead. Both metals are toxic even in minute concentrations.
More than a lack of quality control
That there’s no enforceable quality control over supplements presents one set of problems. There’s also the fact that a particular supplement may be harmful for a particular dog. For example, Dr. Freeman says, some owners give hawthorn to their dogs with heart disease. It is touted as a “natural” remedy. But hawthorn has effects similar to the drug digitalis, so if the dog is already taking that drug, the two together could have toxic effects.
Other owners give antioxidants to their dogs with cancer, having gone on the Internet and read that antioxidants protect against malignancies. But radiation and many chemotherapy drugs work specifically by causing oxidation of cancer cells. Antioxidant supplements could limit the effectiveness of those treatments.
Keep in mind, too, that dogs don’t even require the antioxidant vitamin C. In fact, in high doses, it can increase a dog’s risk for developing certain types of bladder stones. And too much vitamin E, another antioxidant, can predispose a dog to excessive bleeding.
In many cases — and Dr. Freeman hears about this frequently — people don’t know the right dose of a supplement for their dog. They’ll go to the store, buy a supplement meant for people, and then give half the recommended dose to their pet. “But if your pet is a Dachshund,” Dr. Freeman points out, “half the dose for a human adult is still a lot. Also, dogs and people have different metabolisms, so there are ingredients that are safe for people that are not necessarily safe for dogs. They may absorb something too quickly or metabolize it differently, for instance.”
The bottom line: Don’t give your dog supplements unless your veterinarian tells you to. If your dog is healthy, there’s absolutely no reason even to consider supplements. A good quality dog food that has undergone feeding trials approved by the American Association of Feed Control Officials (AAFCO), or is formulated to meet AAFCO profiles, contains everything your pet needs to maintain good health. (The food label will give you the AAFCO information.)
If your dog is deemed to need supplements, your vet should be able to recommend a brand. The doctor is in a better position to make sure there will be no negative effects. Alternatively, you can talk to a board-certified veterinary nutritionist (see acvn.org).