Although bleeding and hemorrhage are the classic signs of vitamin K deficiency, they occur only in severe cases.
Vitamin K deficiency is considered clinically relevant when prothrombin time is significantly increased due to the decreased prothrombin activity of blood.
Daily adequate intakes for women and men aged 18 years and younger is the same, at 75 µg.
Adequate intake in women who are 19 years or older is 90 µg, compared with 120 µg for men of the same age.
Pregnancy and lactation considerations do not change the adequate intake.
Although antibiotics may damage vitamin K–producing bacteria in the gut, supplementation is not usually necessary unless antibiotic use lasts longer than several weeks in patients with poor vitamin K intake.
Vitamin K may have potentially serious interactions with anticoagulants such as warfarin.
Vitamin K deficiency can occur in any age group but is encountered most often in infancy.
