Not all supplements have the same benefits, and not all have the same level of safety.

In canine joint nutrition, three different situations coexist:

• ingredients whose efficacy remains poorly documented;
• poorly formulated or heavily under-dosed products;
• certain ingredients or excipients that may pose a real risk to dogs.

The purpose of this article is not to mention specific brands or products, but to present the main situations described in veterinary literature.

Why is the market difficult to understand?

Dietary supplements are not evaluated according to the same criteria as veterinary drugs.

A drug must demonstrate its efficacy and safety before it can be marketed.

Supplements fall under a different regulatory framework. They must be manufactured under appropriate conditions and have compliant labeling, but they are generally not subject to the same level of clinical evaluation.

This difference explains why a product can be marketed even though its efficacy has never been studied in dogs.

It also explains why two products containing the same ingredients can have very different quality levels.

Glucosamine and chondroitin

Glucosamine and chondroitin are probably the most well-known examples.

They are very common in joint supplements for dogs and still benefit from strong marketing enthusiasm, often because they have long been associated with "joint health."

The problem is not the safety of these ingredients, which appears to be generally good.

However, the meta-analysis by Barbeau-Grégoire et al. published in 2022 reports a very weak, or even absent, effect on osteoarthritic pain in dogs and cats.

These results make it difficult today to present this combination as an essential reference in the management of joint pain.

Poorly bioavailable curcumin

Curcumin has interesting biological properties experimentally.

However, its oral bioavailability is low, and the available clinical data in dogs remain limited.

A product containing simply turmeric or curcumin cannot therefore be considered a proven joint anti-inflammatory in the absence of a studied formulation and specific data in dogs.

Caution is also necessary in dogs already receiving anti-inflammatory treatment or other medications. Curcumin can interact with certain metabolic pathways and modify the effect of associated treatments. In a dog on NSAIDs, anticoagulants, antiplatelets, or chronic treatment, its use must therefore be absolutely discussed with the veterinarian.

Vegetable oils rich in ALA

Some vegetable oils are marketed under the generic term "omega-3."

Alpha-linolenic acid (ALA) found in vegetable oils does not have the same biological profile as marine EPA and DHA studied in canine osteoarthritis research.

The use of the term "omega-3" without specifying the actual amounts of EPA and DHA can therefore lead to confusion.

Formulas without identifiable dosage

Some products combine many ingredients without precisely indicating their quantities.

In this context, it becomes impossible to compare the product with the doses used in scientific studies.

These formulations do not necessarily pose a particular risk, but their actual benefit remains difficult to assess.

Xylitol

Xylitol is probably one of the most important risks to be aware of.

In dogs, it can cause a massive release of insulin, leading to severe hypoglycemia. Serious liver damage has also been described.

The thresholds reported in veterinary literature are around:

• 0.1 g/kg for the risk of hypoglycemia;
• 0.5 g/kg for the risk of liver damage.

Chewable products, certain human supplements, or some "sugar-free" products must therefore be checked carefully.

Vitamin D

Vitamin D becomes toxic in cases of overdose.

Poisoning can lead to:

• vomiting;
• lethargy;
• increased thirst;
• increased urination;
• hypercalcemia;
• kidney failure;
• tissue calcification.

Poisonings mainly concern human products or administration errors.

Alpha-lipoic acid

Alpha-lipoic acid should not be confused with alpha-linolenic acid from vegetable oils.

This antioxidant found in some human supplements can cause:

• vomiting;
• hypoglycemia;
• neurological disorders;
• convulsions;
• liver or kidney damage.

Cats are particularly sensitive to it, but dogs can also be poisoned.

Iron

Iron poisoning mainly concerns human multivitamins.

Depending on the ingested doses, it can cause:

• digestive disorders;
• acidosis;
• cardiovascular damage;
• shock;
• liver lesions.

This risk primarily concerns accidental ingestion of human-intended products.

Actual content and labeling

The actual quality of the products poses another difficulty.

ConsumerLab reported that several animal supplements did not match the advertised concentrations.

Some products contained much lower quantities than indicated on the label.

High levels of certain contaminants have also been reported in some cases.

A product can therefore be ineffective not because the ingredient doesn't work, but because the product doesn't actually contain what it advertises.

Human supplements

Many poisonings occur after the administration of products intended for humans.

Xylitol, certain vitamins, iron, or alpha-lipoic acid are among the most frequently cited ingredients.

A human supplement should therefore not be given to a dog without veterinary advice.

Differences in metabolism between species make certain substances much riskier for dogs.

Products that are sometimes useless rather than dangerous

Not all uninteresting products are toxic.

Some formulas are simply heavily under-dosed, poorly constructed, or based on extrapolations from human medicine.

The risk then is mainly to waste time, delay appropriate care, or give the impression of acting while the joint problem continues to progress.

Useful checks before buying a supplement

Before using a supplement, it may be useful to:

• read the entire composition;
• check the excipients;
• look for the presence of xylitol or other problematic substances;
• verify that the product is intended for dogs;
• ask for veterinary advice in case of chronic illness or ongoing treatment.

Sources

1. Finno C.J. et al. (2020/2021). Veterinary Pet Supplements and Nutraceuticals.

2. Merck Veterinary Manual. Xylitol Toxicosis in Dogs.

3. MSD Veterinary Manual. Toxicoses in Animals From Human Dietary and Herbal Supplements; Toxicoses in Animals From Human Multivitamins and Supplements.

4. Barbeau-Grégoire M. et al. (2022). Meta-analysis on enriched diets and nutraceuticals in canine/feline osteoarthritis.

5. ConsumerLab. Review on joint supplements and animal products.

6. Piscitelli et al. / Dunayer on xylitol toxicity in dogs.