Vitamin K is a name given to a group of fat-soluble vitamins that have similar structures. Naturally, two forms exist, the K1 or phytonadione and K2 or menaquinone vitamer.
However, there is a K3 or menadione which is a synthetic form.
Its common sources are green leafy vegetables such as collards and mustard greens, spinach, kale, parsley among others as well as vegetables like broccoli, cauliflower, brussels sprouts and cabbage. Also, fish, eggs, liver, meat, and cereals have small amounts of this vitamin.
Being fat-soluble, dietary vitamin K tends to be absorbed more if it is accompanied by foods that have some short to medium-chain fats. However, polyunsaturated fats often hamper absorption.
Should it be supplemented?
Before we give you an answer, you deserve to know that this vitamin can be available in form of tablets, capsules, or liquid over the counter. The injectable ones are often stronger and require a prescription.
For a cat that weighs about 9 pounds and requires 250 calories of food daily, The National Research Council of the National Academies recommends the amount of vitamin K to be 82 µg.
The NRC puts the amounts at 1.0mg/kg of food while the Association of American Feed Control Official (AAFFO) recommends 100µg per kilogram of feed. 
Since bacteria in the large intestines of cats can synthesize vitamin K, a deficiency may only arise if their diets do not promote the growth of these bacteria. Therefore, it should not be added to cat foods unless fish is over 25% of the dry matter.
Finally, there has been no report of toxicity due to overdose (over supplementation) and the issue of whether to supplement or not is not clear unless there are symptoms of deficiencies.
However, there is a possibility of interaction with other medications or hypersensitivity reactions.
It works as a co-factor for several enzymes and without it, they cannot be active. Some of its functions include the following:
- It acts as an enzyme γ-glutamyl carboxylase cofactor which in turn modifies several coagulation factors (II, VII, and X) and hence enabling blood coagulation to occur. Calcium is also necessary during the coagulation.
- As Royal Canin states, it plays an important “role in protein metabolism, helping to bind calcium in bone.”
Besides these functions, this vitamin is also considered for preoperative prophylaxis and it can be given a day or two before the operation.
Rodenticide toxicity and vitamin K
Rodenticide toxicity in cats results from these animals eating rodent poison or rodents that have been poisoned. The poison can either be anticoagulant or non-anticoagulant.
The anticoagulation inhibits vitamin K activation and since it is necessary for blood clotting, the rodent or cat that takes such poison bleeds externally or internally until it dies. Examples of such rodenticides include warfarin (short-acting anticoagulant) while bromadiolone, pindone, diphacinone, and brodifacoum are long-acting.
Treating rodenticide poisoning in cats requires a combination of both subcutaneous and oral vitamin K1 where prescription brands such as Veta-K1®, Mephyton® or Veda-K1® are given.
More details on rodenticide poisoning in cats and treatment will be discussed in a different article.
Vitamin K deficiency signs
Deficiencies are mainly caused by anticoagulant rodenticide toxicities. Other causes include reduced absorption or intake due to intrahepatic cholestasis, absence in diets, intestinal disease (affects absorption), biliary obstruction as well as medications especially sulfaquinoxaline.
Also, there has been noted a deficiency in the Devon Rex cat breed due to congenital γ-glutamyl carboxylase defect.
In case of deficiencies, some of the possible symptoms of deficiencies include the following:
- Since it acts as a cofactor in blood clotting, a deficiency will lead to skin, nasal, cerebral and digestive hemorrhages. Even though they might be small, these hemorrhages can lead to anemia with time.
- Prolonged clotting even in superficial cuts
Menadione sodium bisulfide in cat food
Due to the toxicity associated with menadione and large doses of its derivatives, it is common to for many pet owners to look for cat food without menadione sodium bisulfide complex.
However, you need not worry much, according to the European Food Safety Authority, “menadione sodium bisulfide (MSB) and menadione nicotinamide bisulfide (MNB) is safe for all animal species at practical use levels in feed.”
However, if MSB is added to water then there is a possibility of your cat being exposed to hexavalent chromium or chromium (IV). Therefore, it should not be added to water.