Vitamin K deficiency is uncommon in healthy adults because gut bacteria produce some K2 and small amounts are stored in tissues. The main concern is vitamin K deficiency bleeding (VKDB) IN newborns — a potentially fatal condition. All US newborns receive a vitamin K injection at birth to prevent it. In adults, deficiency primarily affects people on long-term antibiotics, those with severe fat malabsorption, or warfarin users.
Common symptoms
Easy bruising and prolonged bleeding from minor cuts
Bleeding gums, frequent nosebleeds
Heavy menstrual bleeding
Blood in urine or stool (dark, tarry stools)
Internal bleeding — especially gastrointestinal
In newborns with VKDB: bleeding from the umbilical stump, mucous membranes, GI tract, or — most seriously — into the brain (intracranial hemorrhage)
Signs of internal bleeding in infants: extreme sleepiness, pale skin, bulging fontanelle, vomiting, seizures (MEDICAL EMERGENCY)
Increased risk of bone fractures (chronic deficiency affects bone metabolism via osteocalcin)
At-risk groups
Newborns who do not receive prophylactic vitamin K injection at birth
Exclusively breastfed infants (breast milk is low in vitamin K)
Infants with cholestatic liver disease, biliary atresia, or cystic fibrosis
People taking warfarin or other vitamin K antagonists (intentional, requires monitoring)
People on long-term broad-spectrum antibiotics (alters gut flora)
People with severe fat malabsorption (Crohn's, celiac, short-bowel syndrome)
People with chronic liver disease
People who've had bariatric surgery
When to see a doctorAny unexplained bleeding in a newborn — bleeding from the umbilical stump, blood in stool, vomiting blood, or signs of brain bleeding (extreme sleepiness, seizures) — is a MEDICAL EMERGENCY requiring immediate ER care. In adults, unexplained easy bruising or bleeding warrants a coagulation panel (PT/INR). Do NOT take vitamin K supplements if you are on warfarin without your doctor's approval — it can dangerously alter your medication's effect.