The Supplement Problem No One Is Talking About

I've spent a lot of time over the past year helping clients think through supplement strategy. What categories to enter, how to formulate, and how to position the product. And one question keeps coming up that the industry hasn't answered very clearly: How do you actually know what's in the product you're selling?

A recent study published made me sit with that question a little harder. In the study, researchers tested 70 over-the-counter canine and feline dietary supplements purchased from a major online retailer, analyzing each for five essential minerals and 12 heavy metals. They also compared actual mineral concentrations to label claims for any product that made them.

The headline finding is that none of the supplements exceeded the National Research Council (NRC) Maximum Tolerable Levels (MTLs) for any mineral, including the heavy metals tested. That's worth saying, because this isn't a product safety recall story. But when you read past the headline, the bigger picture is more complicated and more relevant to anyone building or scaling in this category.

Across all 70 products, the researchers recorded 376 heavy-metal detections. Only one product contained no detectable heavy metals. Every other product in the study (69 out of 70) had at least one.

The most prevalent heavy metal was nickel, found in 66 of 70 products (94.3%), followed by barium in 64 products (91.4%) and vanadium in 61 products (87.1%). Lead was detected in 16 supplements (22.9%), with concentrations of up to 3.7 mg/kg. Cadmium was detected in 10 products (14.3%), with concentrations up to 1.5 mg/kg. Arsenic was found in 19 products (27.1%).

These aren't trace amounts you have to squint to find. They're present because heavy metals enter the supply chain through natural mineral contamination of raw ingredients, including soil, water, and plant material. Without robust ingredient specification and testing, they pass straight through into the finished product.

One finding in particular stuck with me. A product explicitly marketed for liver support, with claims to help the animal's body avoid exposure to heavy metals, contained five detectable heavy metals: vanadium, chromium, cobalt, nickel, and barium. That's not a safety violation; it's a credibility problem. And it illustrates what can happen when formulation and quality control aren't working in sync, and why heavy metal testing needs to be a deliberate, standalone part of a brand's quality program. Guaranteed analyses and standard label claim verification don't screen for heavy metals. That requires proactive, targeted testing at the ingredient and finished-product levels, something most brands aren't doing unless they've built it explicitly into their quality protocols.

The Selenium Story Is Its Own Warning

The essential mineral findings deserve their own attention. Selenium is an essential nutrient, but it has one of the narrowest margins of safety of any mineral in companion animal nutrition. The selenium maximum for dogs set by the Association of American Feed Control Officials (AAFCO) is 2 mg/kg dry matter, which isn't far above the minimum required amount of .35 mg/kg. The present study found selenium in 52 of 70 products (74.3%), with concentrations up to 14 mg/kg supplement, as-fed.

What matters is that selenium was only declared as an added ingredient in 10 of those 52 products. The other 42 contained selenium that pet owners, and probably most formulators, would have no reason to expect to be there.

The authors flag a specific scenario worth thinking through. If a small dog or cat is consuming a primary diet that meets the AAFCO selenium minimum and is also receiving a supplement containing meaningful selenium concentrations, the total daily intake can exceed the AAFCO maximum. The concern scales upward for smaller animals because supplement dosing is based on body weight, but calorie requirements, and therefore primary food intake, scale to metabolic body weight. A 4.5-kg cat consuming a selenium-containing supplement at the label dose can end up in a different risk category than a 30-kg dog consuming the same product.

And then there's the stacking question. The authors cite a survey in which 66% of dogs receiving supplements were receiving more than one supplement simultaneously. Their analysis assumed a single supplement was being used. Add a second or third product, and the cumulative mineral picture changes meaningfully.

The label accuracy findings are worth noting, too. Of the 18 products that made quantitative claims for one or more of the minerals analyzed, eight of them (44%) failed to meet at least one label claim. Of those eight, 87.5% were multivitamin/mineral supplements.

Of the 53 total label claims across those products, 77.4% were met or exceeded. That sounds reasonably good until you look at what “exceeded” sometimes means: seven products had detected concentrations of at least 200% of the claimed content. One contained 331% of its claimed iron. Another contained 443% of its claimed zinc. On the other hand, three products had less than 60% of the claimed content for at least one mineral.

Those numbers matter beyond the spreadsheet. Chronic excess zinc intake in dogs can cause hemolytic anemia, liver and pancreatic damage, and acute kidney failure. The tricky part is that supplement-sourced overexposure tends to creep up slowly. A pet owner who's diligently giving their dog a daily joint chew has no reason to suspect the product is delivering more than four times the zinc on the label. By the time clinical signs appear, the damage may already be underway. On the flip side, three products had less than 60% of their claimed content for at least one mineral, meaning some pets aren't getting anywhere near the therapeutic dose the supplement was purchased to deliver.

This isn't a new problem. Research has documented label inaccuracies in pet supplements for years. One study found that 84% of chondroitin sulfate products deviated from their label claims, with deviations ranging from 0% to 115%. What the present study adds is current, systematic data across a broader supplement category.

The practical takeaway is straightforward. A label claim is not a quality assurance system. It's a starting point that requires independent verification to be meaningful.

The Feline Problem Within the Problem

Something the study surfaces quietly, but that deserves louder attention in our industry, is that we don't have species-specific MTL data for cats. The NRC has established canine MTL values only for cadmium and lead. For cats, there are no NRC MTL values for any of the minerals analyzed in this study. The researchers had to apply the same MTL values to both cat and dog data, and where species-specific values didn't exist, they used MTL derived from rodents, poultry, or swine.

The authors are candid about the limitations. For cats, they note that comparisons to omnivore livestock species are particularly weak because cats are obligate carnivores. Better reference points might be mink or other fur-bearing carnivores, for which essentially no data on tolerable levels exist.

This matters for two reasons. First, cats metabolize many compounds differently from dogs, which means that certain compounds clear more slowly, while chronic low-level exposures can accumulate in ways that wouldn't be predicted from dog or human data. Second, the cat supplement segment is growing faster than any other pet type in the category. MarketsandMarkets projects a 9.1% CAGR for cat supplements through 2030. Increased use of feline supplements against a backdrop of inadequate feline-specific safety data is a dangerous combination that the industry should be paying attention to.

Why NASC Matters

This is the part of the conversation I want to spend more time on. And I'll be honest, quality claims in the pet supplement space can feel like shades of grey. 'Tested,' 'verified,' 'third-party certified' get applied so loosely that they've largely lost meaning. That credibility gap is real and worth naming. What separates a genuine quality infrastructure from a marketing badge is whether it creates verifiable, auditable accountability at the points where things actually go wrong: ingredient sourcing, manufacturing consistency, label accuracy, and post-market safety surveillance.

The National Animal Supplement Council (NASC) Quality Seal is consistently misunderstood as a marketing badge rather than a quality-infrastructure requirement. However, the supplement findings in this study are exactly the failure modes the NASC process is designed to catch. It cannot be prevented entirely, because no system eliminates all risk, but it can detect, track, and correct.

To earn the NASC Quality Seal, a company must pass a comprehensive independent third-party audit, a process that typically takes about four months from start to finish. The audit covers documented standard operating procedures for production process controls, labeling compliance against NASC guidelines, and verification that products are registered in the NASC adverse event reporting database. The audit certificate must be renewed every two years; there's no grandfathering. Companies must also pass random independent product testing to verify that what's on the label is what's in the product.

Run the study findings through that framework. Selenium showing up undeclared in 74% of products? That's an ingredient specification and testing failure that an audit-ready quality control system would catch. A product claiming 443% of its labeled zinc? That's a batch-level manufacturing inconsistency that random independent testing would surface. A liver support product containing multiple heavy metals despite marketing language around metal avoidance? That's a formulation and claims review failure that NASC's labeling compliance process exists to prevent.

None of this means NASC certification guarantees perfection, but it creates accountability structures that the unregulated default does not.

The Business Case for Getting This Right

Here's what I’ve seen work when working with supplement brands at different stages. Quality infrastructure tends to get treated as a later-stage problem. First, you build the product, establish distribution, and prove the market, then you worry about audits and SOPs. That sequencing creates real downstream risk.

Veterinary channel access is increasingly quality-credential-dependent. Retailers are asking harder questions about third-party testing, and the conversation happening in the research community right now will reach the retail floor and the veterinary exam room faster than most brands anticipate.

There's also a differentiation argument that isn't made often enough. This study, and the broader literature it builds on, create a genuinely useful commercial conversation for any brand that has done the work. In a market where 69 out of 70 randomly selected products contain at least one detectable heavy metal and nearly half of quantitative label claims on multivitamin products don't fully hold up, transparency is a competitive position. A brand that can point to its NASC audit certificate, its independent testing Certificates of Analysis (CoAs), and its ingredient-level heavy metal specifications is telling a fundamentally different quality story than one that can't.

The challenge, and I hear this regularly, is that building the quality infrastructure and the product simultaneously, while managing a launch, feels overwhelming. But, it doesn't have to be. The NASC audit process is structured and learnable. Ingredient specification development and supplier qualification don't require a large internal team if you're approaching them systematically. And the investment in getting it right early is considerably smaller than the cost of fixing it later.

What I'd Be Asking If I Were You

If you're currently selling supplements: When did you last run independent testing on your current formulations? Does your CoA come from your manufacturer or from an independent lab? Do you have heavy metal specifications written into your ingredient purchasing agreements?

If you're developing a new supplement line: Are your formulation decisions and your quality control (QC) infrastructure decisions happening in parallel, or sequentially? Have you mapped your label claims against independent verification?

If you're thinking about the feline category specifically: Are you applying dog-centric safety assumptions to a species that metabolizes compounds meaningfully differently, with essentially no species-specific tolerable level data to lean on?

This study doesn't say the sky is falling. It says we're building a multi-billion-dollar category on a quality foundation that hasn't been fully validated. The data to start asking harder questions is now clearly in the literature. The frameworks to start answering them, starting with NASC, already exist.

The questions this study raises don't have easy answers, but they do provide a starting point. If you want to go deeper into the regulatory and quality aspects of supplement formulation, BSM Partners' team recently covered much of this ground in our podcast episode "Wrangling the Wild West of Pet Supplements" with Dr. Stephanie Clark and Jordan Tyler. And if your brand is actively navigating supplement quality, NASC audit readiness, or label compliance, that's exactly the kind of work our FSQAR practice was built for. We help clients build the quality infrastructure that makes those questions answerable, before they become problems.

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About the Author

Neeley Bowden Lewis is a Manager of Special Services on the BSM Partners Product Innovation team. She earned her bachelor's degree in pet food production and her master's in food science. In her early career, she worked in product innovation of pet food ingredients, focusing on the development of palatability enhancers. Bowden Lewis calls Arizona home, along with her faithful canine, Allie.