The hallmark is a tendency to bleed: easy bruising, gum or nose bleeding, and prolonged bleeding from small cuts. Severe deficiency can increase the risk of internal bleeding and is a medical urgency. In adults, clinically significant deficiency is more often linked to malabsorption (e.g., celiac disease, inflammatory bowel disease, cholestasis), prolonged broad-spectrum antibiotics, or serious liver disease rather than diet alone. Newborns are vulnerable due to low stores, which is why vitamin K prophylaxis is standard. If deficiency is suspected, evaluation should focus on clotting tests and identifying underlying causes.