Vitamin K is one of those nutrients that we learn of early
in nutrition training as an essential fat soluble vitamin that
is important in clotting. Beyond that, we seldom discuss it.
Recently, however, there has been a concerted effort by a few
"pet enthusiasts" to spook petfood manufacturers and
well-meaning pet owners into the notion that vitamin K
supplementation in the diet, specifically with vitamin K3
(menadione), is unnecessary and potentially toxic to pets.
Determining whether they have a valid point warrants a bit of
Vitamin K is known principally for its role in blood
clotting, but has also been reported to be involved with
osteocalcin and bone formation, along with a number of other
biomedical functions. By definition, vitamin K is any of
several compounds that are based on 2-methyl-1,4-napthoquinone
(also known as menadione) that express anti-hemorrhagic
properties (Suttie, 2007). The amount of vitamin K recommended
for dogs and cats is approximately 1 part per million of the
diet (NRC, 2006).
Vitamin K can be supplied to the animal from a combination
of sources: vitamins K1, K2 and K3. Vitamin K1, also known as
phylloquionone, is found in green leafy vegetables and
vegetable oils. Vitamin K2 is produced by gut bacteria and
vitamin K3 is chemically synthesized. Vitamins K1 and K2 are
"active" upon absorption. However, vitamin K3 must be
"alkylated" by gut bacteria or tissue enzymes to become active.
This activation involves the addition of isoprenoid side
chains, and in some literature this activated form is called
menaquinone or designated as MK-4.
While it is true that most of the dietary vitamin K can be
provided by vitamin K1 from green leafy plants and vegetable
oils, or through stable gut fermentation (supplying vitamin
K2), the variability in these sources, effects from processing
and gut health of the animal make them less than 100% reliable.
Further, not every petfood company considers green leafy
vegetables or vegetable oils to be an essential part of a dog
or cat diet. So, many petfood companies choose to supplement
with a commercial source. These commercial sources of vitamin
K3 are produced through industrial synthetic chemistry. The
(2007) lists only vitamin K3 sources as approved for use. They
include menadione dimethylpyrimidinol bisulfite (MDPB),
menadione nicotinamide bisulfite (MNBS) and menadione sodium
bisulfite complex (MSBC).
None of these are explicitly identified for use in petfoods,
but no objections have been forthcoming if MSBC is the vitamin
K3 source of choice. No forms of vitamin K1 or K2 are approved
as feed ingredients, although there is an understanding that no
regulatory action will be taken for pre-market approved use of
vitamin K1. So, even if a petfood company gave in to these
unfounded concerns over vitamin K3, they don't really have any
other option besides vitamin K3 to use as the supplement unless
they choose to completely remove it from the formula
As for the toxicity concerns, there are no reports of
nutritional toxicity of any vitamin K sources in dogs or cats
readily available in the literature, and certainly no
descriptions that could be found showing vitamin K3 (menadione)
was harmful to dogs, cats or other domestic animals. The recent
Nutrient Requirements of Dogs and Cats
(NRC, 2006) and the
Vitamin Tolerances of Animals
(1987) texts are authoritative reviews on the topic, and they
state that toxicity of menadione by nutritional routes is in
excess of 1,000 times the requirement. Further, vitamin K3 has
been fed to poultry, swine and companion animals for more than
50 years without incident. So, nutritional supplementation with
vitamin K3 doesn't appear to be a smoking gun.
However, the pharmacological or medical use of vitamin K to
combat acute ingestion of anti-clotting agents (e.g., warfarin
or coumarin) and bleeding disorders of neonates (human)
associated with vitamin K deficiencies is a different story.
Under these circumstances and dosages, vitamin K1
(phylloquinone) is the preferred intravenous (parenteral)
source of vitamin K. Further, it has been demonstrated that
intravenous administration of vitamin K3 at dosages of 100
mg/kg (which is around 100 times the nutritional requirement)
may be toxic. One can speculate that this could be due to the
lack of "alkylation" that occurs when vitamin K3 is
administered through a route other than via the gut.
Necessary and nontoxic
While small amounts of vitamin K are required in the diet
and might be provided by whole ingredients or healthy gut
fermentation, the uncertainty of these sources leads many
petfood companies to supplement with commercial vitamin K3
(menadione). To provide this wee bit of "insurance" in the
petfood, there is only one form availablethe water soluble,
stabilized menadione (MSBC). Judicious use of nutritional
vitamin K3 is clearly not toxic, so this notion that vitamin K3
as an ingredient in petfoods should not be used is unfounded
and should be reversed. Further, it is hoped that through
education and communication, consumers can be made aware that
not all that is printed on enthusiasts' websites is correct.
Also, radical nutrition positions should be compared and
contrasted with current and comprehensive research literature
and not just a few, potentially unrelated, experiments.
The question is whether they provide additional benefit to the dog or cat
What is this quiet, unassuming ingredient, and should it be there?
It's an "Intel inside" type of molecule -- but also a problem child
It's the finishing touch that can meet both owner and pet needs.
--- Thank you for your patience ----
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