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Warfarin overdose and coumarin poisoning
Vitamin K is one of the treatments for bleeding events caused by overdose of the anticoagulant drug warfarin (Coumadin®). Vitamin K is also part of the suggested treatment regime for poisoning by rodenticide (coumarin poisoning).

Vitamin K deficiency bleeding in newborns
The blood clotting factors of newborn babies are roughly 30–60% that of adult values; this may be due to the reduced synthesis of precursor proteins and the sterility of their guts. Human milk contains 1–4 μg/L of vitamin K1, while formula-derived milk can contain up to 100 μg/L in supplemented formulas. Vitamin K2 concentrations in human milk appear to be much lower than those of vitamin K1. Occurrence of vitamin K deficiency bleeding in the first week of the infant's life is estimated at 0.25–1.7%, with a prevalence of 2–10 cases per 100,000 births.[72] Premature babies have even lower levels of the vitamin, so they are at a higher risk from this deficiency.

Bleeding in infants due to vitamin K deficiency can be severe, leading to hospitalization, blood transfusions, brain damage, and death. Supplementation can prevent most cases of vitamin K deficiency bleeding in the newborn. Intramuscular administration (known as the Vitamin K shot[73]) is more effective in preventing late vitamin K deficiency bleeding than oral administration.[74][75]

United States
As a result of the occurrences of vitamin K deficiency bleeding, the Committee on Nutrition of the American Academy of Pediatrics has recommended 0.5–1 mg of vitamin K1 be administered to all newborns shortly after birth.[74]

United Kingdom
In the UK, vitamin K supplementation is recommended for all newborns within the first 24 hours.[76] This is usually given as a single intramuscular injection of 1 mg shortly after birth but as a second-line option can be given by three oral doses over the first month.[77]

Controversy
Controversy arose in the early 1990s regarding this practice, when two studies suggested a relationship between parenteral administration of vitamin K and childhood cancer.[78] However, poor methods and small sample sizes led to the discrediting of these studies, and a review of the evidence published in 2000 by Ross and Davies found no link between the two.[79] Doctors reported emerging concerns in 2013,[80] after treating children for serious bleeding problems. They cited lack of newborn vitamin K administration as the reason that the problems occurred, and recommended that breastfed babies could have an increased risk unless they receive a preventative dose.

Osteoporosis
There is no good evidence that vitamin K supplementation benefits the bone health of postmenopausal women.

Cardiovascular health
Adequate intake of vitamin K is associated with the inhibition of arterial calcification and stiffening, but there have been few interventional studies and no good evidence that vitamin K supplementation is of any benefit in the primary prevention of cardiovascular disease.

One 10-year population study, the Rotterdam Study, did show a clear and significant inverse relationship between the highest intake levels of menaquinone (mainly MK-4 from eggs and meat, and MK-8 and MK-9 from cheese) and cardiovascular disease and all-cause mortality in older men and women.

Cancer
Vitamin K has been promoted in supplement form with claims it can slow tumor growth; however, no good medical evidence supports such claims.