Watch Out for This Synthetic Vitamin — It's a Liver Toxin

Analysis by Dr. Karen Shaw Becker

synthetic vitamin k in cat food

Story at-a-glance

  • Menadione and menadione sodium bisulfite complex (MSBC), synthetic forms of vitamin K, are widely used in pet food though they are only approved for use in poultry feeds
  • Menadione and MSBC can be found in all types of pet food, including a few commercial raw diets, so regardless of the type of pet food you buy, it’s important to check labels carefully for the presence of this synthetic nutrient
  • Pet food producers use menadione because it’s an inexpensive and stable ingredient, however, it lacks many of the important properties of natural vitamin K derived from whole foods
  • Menadione has been identified as a liver toxin; even in very small amounts, ingestion of this synthetic vitamin on a daily basis over a dog’s or cat’s lifetime is cause for concern

Menadione, a synthetic form of vitamin K, is a widely used ingredient in pet food. According to, from a strictly regulatory standpoint, there’s been no issue for decades with this additive. Both menadione and menadione sodium bisulfite complex (MSBC) are allowed in pet foods as “vitamin K active substances,” even though the FDA has sanctioned their use in poultry feeds only.1

Unsurprisingly, even though these faux versions of vitamin K are allowed only in poultry feed, the FDA notes on its website that they’re widely used in feeds for other species, including pet foods. As board-certified veterinary nutritionist Dr. David Dzanis explains in a recent article:

“… despite lacking formal approval, this reference to their use for feeds other than for poultry without explicit objection has allowed regulators to exercise enforcement discretion and tolerate the unfettered use of MSBC in pet foods.”2

My take: Menadione and MSBC are yet two more unapproved and potentially toxic additives that are found in pet food in flagrant violation of regulations prohibiting their use. According to Dzanis, recently “at least one state feed control official has taken action against any pet product containing MSBC.”

Apparently, the state for which this feed control official works uses a more literal interpretation of “unapproved for use” than is the norm. Said another way, as the state sees it, “no means no” with regard to the use of menadione/MSBC in pet food.

This presents quite a snafu for pet food manufacturers who sell products containing MSBC in that particular state:

“Urging of the state to exercise enforcement discretion in this instance, or other quick regulatory fixes, such as amendment to the AAFCO listing, appear to be at a stalemate,” Dzanis writes.

Types of Pet Foods Containing Menadione

Veterinarian Dr. Tom Cameron, who I interviewed in 2015 on this topic, has found synthetic vitamin K in every type of pet food, including raw, but its use is especially prevalent in dry and canned foods. As a proponent of raw diets, I was disappointed to discover menadione is used in some commercial raw pet foods.

Most people who advocate raw diets understand that consuming food in its natural form and freshly prepared is optimally healthy. Finding menadione in raw diets tells me that some companies aren’t investigating the ingredients they use. They’re placing their trust in their formulators without actually evaluating each individual ingredient in their food, which concerns me.

So, for all of you out there who haven’t read the fine print on your pet food label — even if you’re buying an excellent quality raw diet — be sure to examine the list of vitamins and minerals closely. If you see menadione or vitamin K3 on the list, you know the food contains a potentially toxic ingredient. For more information on menadione, read this excellent Dog Food Advisor article.

Why Pet Food Producers Use Menadione

The primary reason ultra-processed pet food producers use menadione is that it’s an inexpensive and stable ingredient. It’s much cheaper to make synthetic vitamin K3 in a laboratory than to use natural food-based forms of vitamin K, and cost is a primary driver in pet food manufacturing.

In addition, menadione is a very stable ingredient. Unlike natural vitamins, it isn’t affected by heat, sunlight, storage, dehydration or other factors. Using whole food ingredients in pet food in a way that keeps them stable is a more involved process. Plus, whole food ingredients are more expensive.

Some pet food manufacturers claim they’re using menadione at very low levels, but as Dr. Cameron explains, the difference is that most dogs and cats eat processed pet food their entire lives — sometimes 13, 14, 15 years or longer.

I’m very uncomfortable with even a small amount of a toxic substance given for a decade or two. In veterinary practice, we see many different conditions related to the organs of detoxification. We need to be concerned that, given the barrage of environmental chemicals pets are exposed to, we are adding to the problem by feeding small amounts of known toxins over a long period of time that might be contributing to the dozens of degenerative diseases we see today.

Menadione May Be Toxic to the Liver and Other Organs

Menadione is a synthetic analog, which means it’s man-made. Natural vitamin K is a fat-soluble vitamin that is absorbed through fat metabolism. Menadione is a water-soluble form of vitamin K that works very differently. It is presumably absorbed by bacteria in the gut and converted to forms of vitamin K the body can use.

There are very significant limitations to menadione vs. natural vitamin K. For example, it doesn’t support blood clotting. There are important properties of natural vitamin K that synthetic vitamin K lacks.

Another significant and growing concern about menadione is that it may cause liver toxicity. According to Dr. Cameron, there are many references that classify menadione as a toxin. There are studies from other countries that show that menadione causes toxicity to liver cells and red blood cells.

There are also material safety data sheets (MSDS) that list menadione as a substance that is toxic to the liver, kidneys, lungs, mucous membranes, and other tissues.3 Obviously, it’s a concern when a toxin is being added to foods that pets are fed every day.

What Are the Long-Term Health Effects of Synthetic Nutrients?

Our pets’ bodies (and ours) have evolved over millions of years eating whole foods and efficiently processing nutrients from those foods. There are very specific receptors in the body that are designed to make perfect use of the nutrients contained in real food.

When we start breaking whole foods apart to reproduce their nutrients in the laboratory, we run into lots of limitations. When a synthetic nutrient is created in a lab, the finished product has a different structure from the natural form of the nutrient. Generally speaking, a man-made nutrient doesn’t fit well into the receptor in the body that was designed for that nutrient in its natural state.

The result is that not all components of the synthetic nutrient can be used by the body. It is therefore less efficient, it doesn’t have the same metabolic effect as the real thing, and our bodies must process the unusable portion as a xenobiotic (waste) product. It takes energy to get rid of the waste, which is a drain on the body’s resources.

Some nutrients such as zinc are hard to come by in whole food sources. In these cases, many human grade pet food companies resort to using human quality supplements to supply the handful of mineral deficits commonly found in fresh commercial pet diets. The quality of lab-made nutrients ranges from contaminated to highly purified, unabsorbable to highly absorbable.

Thankfully, amino acid chelates and proteinates provide better absorption and assimilation than many of the cheaper “feed grade” minerals, including the oxides and sulfates found on ingredient panels that pet owners would be best to avoid. In the case of vitamin K, there are safer and healthier choices when it comes to supplementation, but feed grade pet food companies don’t want to spend the money on the more expensive options.

Menadione is a vitamin K analog — a synthetic version of vitamin K. Many people know that vitamin K comes from certain foods, for example, green leafy vegetables and liver. Vitamin K is an important factor in blood clotting. It also drives minerals to certain organs of the body like the teeth and bones, to help them heal and to support connective tissue.

Menadione is called vitamin K3 and as I discussed above, it’s widely used in pet foods to replace naturally occurring vitamin K in order to meet AAFCO nutrient profile standards. For several years now, there’s been a good deal of controversy and concern around the use of this substance in pet food.

According to Dr. Cameron, there are human studies that show long-term use of synthetic vitamins does not have the health benefits we expect. When a nutrient is fractioned and separated from all the other ingredients that create synergy and work together with it, the therapeutic activity of the nutrient is lost.

As with many questionable ingredients in the food supply — another is sodium selenite (synthetic selenium) — there’s an ongoing debate about whether or not they are safe. No long-term safety studies have been done with pets. My perspective, as always, is that it’s much healthier and safer to get the bulk of nutrients, especially vitamins and minerals, from food rather than supplements — in particular poor quality, “feed grade” synthetic supplements.


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