Generally, there are no negative side effects of vitamin K, even if it is taken in fairly large dosages. An allergic reaction, however, might occur in some individuals, but it generally is safe for everyone, including pregnant women. Vitamin K can interfere with nutritional supplements, such as vitamins A and E, as well as with other medications such as anticoagulants. Side effects might also worsen the symptoms of individuals suffering from kidney or liver problems.
There are three types of vitamin K known as phylloquinone (K1), menaquinone (K2) and menadione (K3). Vitamins K1 and K2 are naturally produced and have not been linked to any side effects. The synthetic version, vitamin K3, however, has been linked to oxidative stress. When infants are injected with K3, it can result in hemolytic anemia and a buildup of toxins within the liver. As a result of this, vitamin K3 is not used as often and is banned in some countries altogether.
For individuals who are on kidney dialysis, the side effects have been known to worsen the symptoms that are already present. People who have liver problems might also experience an interference, which could result in excess blood clotting. Individuals who suffer from these conditions should speak with their healthcare provider before taking vitamin K supplements.
Vitamin K tends to work against certain medications, such as anticoagulants. Its role is to thicken and somewhat clot the blood to prevent excess bleeding, while anticoagulants work to thin the blood and prevent dangerous blood clotting. It also is advised that vitamin K should not be taken with other medications or supplements that have an effect that is similar to that of vitamin K, because that can be dangerous and increase the risk of blood clotting. Vitamins A and E, when taken in large dosages have been shown to interfere with the blood clotting action as well.
The maximum vitamin dosage for vitamin K has not been determined because there have not been reports of negative side effects when taken in large dosages. There is, however, an adequate intake (AI) level to help individuals stay within healthy levels and avoid any possible side effects of vitamin K. The daily AI for infants younger than 1 year is 2-2.5 micrograms; for children and adolescents, it ranges from 30-75 micrograms; and for adults, the AI is 90 micrograms for women and 120 micrograms for men. This includes pregnant women because there are no reports of negative side effects of vitamin K when taken by healthy individuals in healthy doses.