Vitamin K in Pet Foods
By Dr. George Collings
Vitamin K, an essential nutrient, was first discovered in 1929 with the observance of a hemorrhagic syndrome in chicks fed a diet in which the sterols were removed by extraction. An anti-hemorrhagic factor was isolated from alfalfa and was identified as substance like Vitamin K. By 1943, two scientists were given a Nobel Prize for the discovery of Vitamin K.
Since then, it has been discovered that green leafy vegetables are good sources of Vitamin K, but it is also found in liver, meat, milk and eggs. Without Vitamin K, there is possible impaired blood coagulation (clotting) in many species. In fact, the name of Vitamin K came from the German description ‘koagulationvitamin’.
Vitamin K is found in three forms (two naturally occurring forms and one synthetic):
Vitamin K1 – known as Phylloquinone – found in plants
Vitamin K2 – known as Menaquinone – synthesized by bacteria in the intestinal tract.
Vitamin K3 – known as Menadione – a synthetic form which is converted to Vitamin K2 in the intestinal tract.
Ingredient Labeling. Most vitamins have common names that are more appealing to the consumer than the chemical – scientific names. For instance, Vitamin E is the common name used on most packages, but the scientific name is alpha-tocopherol and the source is called alpha-tocopherol acetate. Clearly, a common name is appealing, but the scientific name can be daunting and concerning to non-chemists. Another example is Vitamin C which has a chemical name of ascorbic acid. A more stabilized form of Vitamin C is L-ascorbyl-2-polyphosphate. This form is very stable and useful in the prevention of Vitamin C deficiency in birds, fish and guinea pigs. AAFCO labeling rules allow for clarification of chemical ingredient names as a means of clarification and communication. For instance, in the case of Vitamin E (alpha-tocopherol acetate), it can be labeled as Vitamin E Supplement. However, in the case of Vitamin C, it is labeled as ascorbic acid or L-ascorbyl-2-polyphosphate (a Source of Vitamin C).
AAFCO – US FDA and Vitamin K. There are different sources of Vitamin K listed in the Association of American Feed Control Officials’ Official Publication as approved for animal and pet foods. These forms include Menadione sodium bisulfite complex, Menadione dimethyl pyrimidinol bisulfite and Menadione nicotinamide bisulfite. These synthetic forms have shown to be extremely safe by the FDA reporting no adverse reaction in animals.
AAFCO and the US FDA has reviewed the need for all nutrients and published ‘nutrient profiles’ for dogs and cats with acceptable levels of each nutrient in various conditions (maintenance, growth, etc.). Vitamin K is not commonly added in dog food products because the dog is able to obtain all it needs from the bacteria in the intestinal tract or from common ingredients added in the diet. However, Vitamin K is absolutely necessary in cat foods especially if the amount of fish is higher than 25% of the formula. While high fish dog foods are not common in the industry, newer Holistic diets are using higher levels. Adding Vitamin K may be justifiable in these cases.
Not all pet food companies add the qualifier (a Source of Vitamin K) behind the rather large chemical – scientific name of Vitamin K: Menadione dimethyl pyrimidinol bisulfite. The absence of this qualifier has led to confusion among consumers reading chemical – scientific names. In some cases, it has led further concern and mis-information. Some have called Vitamin K as obscure or unnecessary or that it is harmful because of this mis-information. Certainly, the natural forms of Vitamin K (Phylloquinone and Menaquinone) found in green, leafy vegetables are equally as concerning names to a consumer. It is important to note that Vitamin K is essential to dogs and cats, but in most cases is not needed in the food.
Common Mis-Understanding about Vitamin K.
Addressed below are some other frequently stated ‘facts’ about Vitamin K in pet foods found on blogs and other websites:
“Menadione sources of Vitamin K are added to pet foods because they are inexpensive.”
This is not true. Menadione sources are known sources of Vitamin K with predictable and known levels. Common ingredients like alfalfa may have Vitamin K, but the levels may be highly variable and unpredictable. Menadione sources are highly available compared to natural sources which also have variable levels of bioavailability to the pet.
“Menadione is harmful.”
The US FDA has stated that their review of Menadione has shown that up to 1,000 times the requirement level can be used without harmful effects. The only reported case of toxicity occurred in dogs when they ate warfarin (rat poison) and injected high levels of Vitamin K.
“There are scientifically proven side effects of Menadione.”
Some websites have listed a myriad of symptoms and negative effects that have never been documented and are basically hearsay. This has ranged from liver damage, skin irritations, allergy, immune system upsets, etc. Through over thirty years of research and product development in pet foods, I have never seen a documented study connecting Menadione (Vitamin K) to adverse reactions. However, their concern is really inconsequential because it must be remembered that the only time pet nutritionists add Vitamin K to a diet is in cat diets with over 25% fish included. This high level of fish (with higher levels of Omega 3 fatty acids) increases the need for Vitamin K. In these cases, AAFCO requires that 0.1 mg/kg (ppm) be added to the diet in these cases.