Is Menadione – Synthetic Vitamin K safe for your pets?

I have a 14-month-old cat that I love so much. He has been eating Purina Pro Plan Focus – Sensitive Skin & Stomach for over a year. Lately he has seemed to be fed up with the food so I looked for an alternative last weekend. That’s when I came across the controversy of Menadione and started to read upon it. I’d like to share what I have learned so far.

What is Menadione? It’s the synthetic version of Vitamin K, an essential vitamin for humans and animals. The natural version of Vitamin K (K1 and K2) are proven to be harmless, even with high doses. Menadione, on the other hand, can cause several health issues for humans, particularly liver toxicity. In fact, the FDA has long banned the use of Menadione as a supplement for humans, a decision echoed by several studies in Europe.

Although allergic reaction is possible, there is no known toxicity associated with high doses (dietary or supplemental) of the phylloquinone (vitamin K₁) or menaquinone (vitamin K₂) forms of vitamin K. The same is not true for synthetic menadione (vitamin K₃) and its derivatives. Menadione can interfere with the function of glutathione, one of the body’s natural antioxidants, resulting in oxidative damage to cell membranes. Menadione given by injection has induced liver toxicity, jaundice, and hemolytic anemia (due to the rupture of red blood cells) in infants; therefore, menadione is no longer used for treatment of vitamin K deficiency. No tolerable upper intake level has been established for vitamin K.

Source: Oregon State University

Since Menadione is cheaper to produce, pet food manufacturers have every incentive to include this substance to make their products nutritionally complete (on the surface) and commercially cheaper. The question is whether it is legal to do so in the first place.

Here is what the FDA says on the matter, as recently as April 2021:

Although vitamin K is an important nutrient for animals and several sources are available, not all of those sources can or should be used in animal feed. Many have not been approved for use in the United States. 

Menadione dimethylpyrimidinol bisulfite and menadione nicotinamide bisulfite are vitamin K active substances that are regulated as food additives for use in animal feed. Federal regulation 21 CFR 573.620 lays out how menadione dimethylpyrimidinol bisulfite must be used in feed. Menadione dimethylpyrimidinol bisulfite is a nutritional supplement for the prevention of vitamin K deficiency in chicken and turkey feeds at a level not to exceed 2 g per ton of complete feed, and in the feed of growing and finishing swine at a level not to exceed 10 g per ton of complete feed.

Menadione nicotinamide bisulfite is also used as a nutritional supplement for both the prevention of vitamin K deficiency and as a source of supplemental niacin in poultry and swine. Federal regulation 21 CFR 573.625 states that this substance can be added to chicken and turkey feeds at a level not to exceed 2 g per ton of complete feed, and to growing and finishing swine feeds at a level not to exceed 10 g per ton of complete feed.

Before either menadione dimethylpyrimidinol bisulfite or menadione nicotinamide bisulfite could be used in a manner different from that specified in the appropriate regulation, a new food additive petition would need to be submitted and approved by the Food and Drug Administration.

According to NRC’s publication, Vitamin Tolerances of Animals (1987), based on the limited amount of available information, vitamin K did not result in toxicity when high amounts of phylloquinone, the natural form of vitamin K, are consumed. It is also noted that menadione, the synthetic vitamin K usually used in animal feed, can be added up to levels as high as 1,000 times the dietary requirement without seeing any adverse effects in animals, except in horses. Administration of these compounds by injection has produced adverse effects in horses, and it is not clear if these effects would also occur when vitamin K active substances are added to the diet. 

Source: FDA

The fine print clearly says that the FDA only allows the use of Menadione in chicken and turkey feeds. Any other use of the substance will have to be reviewed and sanctioned by the agency. The last time I checked, my cat is a cat, not a turkey or a chicken. Therefore, if a cat food label doesn’t clearly show that it’s approved by FDA, it’s safe to say that from the agency’s perspective, the product is not legal.

The lack of explicit approval from FDA doesn’t deter pet food manufacturers. These companies argue that Menadione is safe for pets because they follow guidelines from AAFCO and that the substance is used in amount that is so much smaller than what AAFCO recommends. Let’s analyze that. Firstly, AAFCO is an NGO that consists of state officials with responsibility for passing and enforcing state laws and regulations with regard to the safety of animal feeds. AAFCO sets the standards and guidelines that these officials often adopt, but the organization itself has no regulatory authority.

Second, when it comes to the role of AAFCO in this debate, it’s important to separate its opinion on Vitamin K from the one on Menadione. The organization does require that “Vitamin K does not need to be added unless the diet contains more than 25% fish on  a dry matter basis“. What this requirement means is that if a diet doesn’t contain fish at all, there is absolutely no reason to include Menadione. When I found out that my cat’s chicken paste from Purina contains Menadione, I was furious. They put a controversial substance in the food even when they don’t have to! And even though Vitamin K is mentioned, AAFCO doesn’t refer specifically to Menadione as an approved source. In fact, here is what the Pet Food Committee Chair of AAFCO had to say on the matter:

Nowhere in Dr Kashani’s response did he mention that Menadione is approved for use in pet food. He clearly relies on the FDA guidelines, which, as mentioned above, only regulate the use of natural Vitamin K sources K1 and K2. Like the FDA, AAFCO only approves Vitamin K3 for poultry feed, not for pet diets. Sadly, pet food manufacturers muddy the waters and use it as a blanket excuse for their inclusion of this supplement in commercial pet products. In a response to a customer’s question, the owner of Weruva said: “according to AAFCO, cat food that contains at least 25% seafood on a dry matter basis must contain a certain level of vitamin K, and according to AAFCO, the only approved source of vitamin k is menadione“. As you can see from the screenshot below, it’s not exactly what is in the rule book.

Among the items discussed in the AAFCO meeting in August 2021 was the use of Menadione. An expert panel commissioned by AAFCO concluded that this ingredient was safe for use in pet foods. Here is the catch. The panel came to this recommendation after reading a white paper written by Purina Pet Foods, which, you may guess, is a pet food manufacturer. The white paper is miraculously deemed confidential and not available to the public eyes. This blatantly flawed process is frustrating and calls into question the recommendation of this so-called expert panel. Without knowing the rational and evidence behind the conclusion, who can say that it’s thoroughly studied and scientifically proven?

I visited a Petsmart and Petco store last weekend. There are a lot of products with Menadione. Apparently, the ingredient has been used in pet food for decades, yet the exact legality of the practice has barely been questioned. Just because something is a long-standing practice without any regulatory approval doesn’t mean that it’s legally allowed. Rules are rules. And if that’s not enough, consider this. We don’t often change our pet diets without cause. The consistent consumption of food with Menadione, albeit with a tiny dose, every day may also accumulate over the long term. And who knows? It may cause serious health issues for our pets. I don’t know about you, but I am not, in good conscience, willing to do it to my beloved cat.