What Are Signs of a Vitamin K Overdose?

The primary signs of a vitamin K overdose are digestive; people usually feel nauseous or queasy, and often vomit. Diarrhea is also common as the body attempts to rid itself of excesses. Young children and those who are immuno-compromised are sometimes also prone to developing jaundice, a yellowing of the skin related to poor liver function; skin rash, irritation, and low levels of iron in the blood have also been reported. Most overdoses aren’t serious and will resolve themselves naturally with time, provided the vitamin’s use is discontinued. Still, if the symptoms persist for more than a day or so, people are usually advised to get medical attention to rule out potentially serious conditions.

Vitamin K is a fat soluble vitamin responsible for the production of blood clotting factor. It is produced by bacteria in the small intestine, and found in green leafy vegetables, meat, and dairy products. The kind found in food is known as vitamin K₁, or phylloquinone. Vitamin K₂, a group of compounds known as menaquinones, is produced in the body. The third kind, vitamin K₃ or menadione, is a synthetic version and most commonly associated with vitamin K overdose. It’s difficult if not impossible to overdose on the vitamin as it occurs in foods, since getting enough to experience reactions would require far more food than normal people could eat. Supplementation and pure extracts are usually where the risk lies.

Vitamin K is available in supplements for people who do not get enough in their diet, as well as those with blood clotting disorders. Most over-the-counter supplements and multivitamins contain vitamin K₁, since it is less likely to be associated with overdose. Additionally, a vitamin K₁ injection is routinely given to newborns in the United States and parts of Europe. A newborn's intestines do not contain bacteria yet, and very little vitamin K is carried in breast milk. Vitamin K overdose in a newborn can be quite serious; as it can cause hemolytic anemia, a serious disorder caused by the premature rupture of red blood cells. Preventing this is usually a matter of paying close attention to dosages and baby weight.

Digestive troubles are among the most common symptoms of an overdose, and usually begin mildly. People may feel a bit queasy shortly after taking the supplements, for instance, and feeling of nausea are usually most pronounced when sitting or standing quickly. Vomiting and diarrhea can occur, too, though if either lasts for more than a day or so medical help may be needed to prevent serious dehydration.

Jaundice is a condition marked by excess bilirubin levels in the blood that the liver is unable to process or filter out. It usually causes the skin and eyes to take on a yellow pigmentation, and can be deadly if not treated. It’s thought that excessive levels of vitamin K in the bloodstream can trigger absorption problems, and in most cases stopping supplementation will reverse the problem.

Anemia, which is a blood iron deficiency, is another possibility. In this instance, the excess K levels can prevent iron from being synthesized from food. Iron deficiency can be serious, so getting the issue corrected promptly is usually quite important.

People experiencing a vitamin K overdose might also develop a rash or patches of itchy, irritated skin. These can occur most anywhere on the body but tend to be most common on the hands and arms. Sometimes the itchiness can be alleviated with creams or ointments, but not always, since much of the actual irritation is internal — it’s just manifesting on the skin.

Pregnant women are generally discouraged from taking vitamin K supplements since the risks to unborn children haven’t been closely studied. In addition, children taking vitamin K supplements should be carefully monitored for symptoms of overdose. Vitamin K₃, which is the most likely to be toxic, is not typically recommended for children at all, and in any event all doses should be carefully monitored and calibrated to the child’s weight.

There can be other problems with vitamin K besides an overdose. Allergic reaction is possible, and more likely with vitamin K₃. People with certain diseases or conditions should consult a health care provider before taking vitamin K. Patients with liver disease may suffer adverse reactions, as will people with glucose-6-phosphate dehydrogenase deficiency. Those with intestinal issues, such as irritable bowel disease, may not be able to fully absorb this vitamin orally, so an injected form is preferred.

Additionally, patients taking warfarin or other blood thinners should not take vitamin K supplements because it can counteract their effects. Those taking blood thinners should also maintain a consistent level of dietary vitamin K consumption. Vitamin K is sometimes given to patients who have taken too many blood thinners. Other drugs and even some herbal supplements can lead to negative interactions, too; as such, it’s important for anyone considering adding this vitamin to consult a health care provider for a more personalized assessment of risk.