the scientific study of pet nutrition by veterinary nutrition specialists and experts.

When Less is More: Sensible Use of Supplements

When Less is More: Sensible Use of Supplements
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We discussed the regulation (or lack thereof) and safety of dietary supplements in an earlier post, but I’d like to address a related problem – excessive use of supplements. We’ve had a number of cases where pet owners were using 3-10+ different products on top of their pet’s normal diet and treats – vitamins, minerals, herbs, joint supplements, etc. At best this is typically a waste of money because of the lack of evidence for the usefulness of the majority of dietary supplements. At worse the supplements themselves can contribute to health problems.

Even if you carefully select supplements that have a good history of meeting their label claims and some data to support a potential benefit, supplements can have interactions with each other, medications, or even with your pet’s regular diet which can lead to adverse health outcomes. Some examples:

  • One of my long-term clients was feeding her dog 15 different supplement products, including 5 geared towards joint health and 3 for dental health, which were health issues that she was very concerned about. I had recommended only 2 of the products. Her dog had persistently increased liver enzymes after adding on the additional supplements. I was worried that supplements and all their unknown and often overlapping ingredients could be contributing and finally convinced my client to stop the majority of them. She called me a month later to tell me sheepishly that the dog’s liver enzymes had normalized, suggesting that one or more of the supplements had been causing liver damage.
  • Another dog presented for high blood calcium and was on many dietary supplements that contained similar nutrients. We couldn’t find an obvious medical cause for the high calcium, but the total levels of some of the nutrients (such as vitamin D) that the dog was getting were concerning, so we advised stopping all supplements. The dog’s calcium levels returned to normal.
  • One of my patients was taking a drug that can increase blood potassium values and was also taking supplements that contained a lot of potassium, in addition to the amount in the diet. The drug plus the added potassium caused his blood levels of potassium to become too high.

As you can see from these examples (and my colleagues and I have plenty more of them!), supplements are not always harmless – they can cause serious health issues. In fact, in people, a study published in the prestigious New England Journal of Medicine suggested that dietary supplements result in over 23,000 human emergency room visits each year!

Here are some tips for making sure you’re not putting your pet at risk with excessive dietary supplements:

  1. Discuss all supplements with your pet’s veterinarian.
  2. Be a skeptic – if you are considering a new supplement, look for evidence that the supplement meets its label claim and is safe.
  3. Compare the nutrients between the products you are using and look for nutrients that are present in more than one product or have a lower threshold for toxicity such as vitamin A, vitamin D, and selenium – add up the amounts of each nutrient that your pet would get from all the supplements and discuss these amounts with your veterinarian.
  4. Avoid products with overlapping ingredients – do not use two products for joints that both contain chondroitin and glucosamine, for instance. While these ingredients are relatively safe, if a higher dose is appropriate, you should be feeding more of one product, not adding on a new product.
  5. If you are using more than 2-3 dietary supplements on top of a commercial pet food, you should carefully consider the reasons and data behind the use of the supplements.
  6. If your pet is eating a commercial pet food, they should not need any vitamin or mineral supplements unless a specific health issue has been identified that might benefit from higher amounts. While vitamin/mineral supplements seem like a safe bet, they have been shown to increase the risk of some health issues in people.
  7. If your pet is eating a home-cooked diet, a standard vitamin/mineral supplement designed for feeding with a regular diet to normal healthy animals is not going to be meeting their nutrient needs – work with a board-certified nutritionist (or visit if your pet is healthy) to design a nutritionally balanced diet for your pet with appropriate supplementation.



Dr. Cailin Heinze is a Board-certified Veterinary Nutritionist® and the Executive Director and Chief Academic Officer of the Mark Morris Institute, a non-profit organization whose mission is to promote optimal companion animal health by providing educational opportunities for veterinary students and veterinarians in clinical nutrition. She has also done some consulting work for Balance IT, a company that makes software and supplements for home-cooked pet diets. She is an expert in home-cooked diet formulation and general pet nutrition and has a special interest in feeding pets with kidney disease and cancer.

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