USNEWS：什么原因导致维生素K缺乏症，以及如何诊断和治疗？

VITAMIN K BELONGS TO A family of fat-soluble vitamins including A, D and E. These vitamins require bile and pancreatic fat-breaking enzymes to digest and absorb. Vitamin K has many roles, but the most important is to promote healthy blood clotting.

How does vitamin K work?

Vitamin K works to activate clotting factors in the blood, and these factors are made by the liver. They include factor II (prothrombin) and factors VII, IX and X. (Vitamin K does activate a variety of other proteins, too, but that’s beyond the scope of this basic lesson.) Improper activation leads to increased risk of bleeding. Certain medications used to reduce the risk of clotting, like warfarin, work by interfering with the activation of this process by vitamin K.

What are the problems related to low vitamin K status?

Low levels of vitamin K are seen in specific settings. In children, low vitamin K-related bleeding problems were once a big problem among newborns – occurring in up to 1 in 200 births – but this was alleviated thanks to routine vitamin administration soon after birth. When vitamin K is poorly transported across the placenta, newborns are at risk for low vitamin K status and bleeding; this is referred to as “vitamin K deficiency bleeding” or “hemorrhagic disease of the newborn.” VKDB is called “early VKDB” when it occurs in the first week of life and “late VKDB” when it occurs in the fist two to 12 weeks of life. VKDB typically manifests as bleeding from the umbilicus, mostly as lots of blood in the stools, or bleeding that stems from the skin or nose. It can also cause sudden bleeding inside the head, especially in late VKDB, which can have a high mortality rate. In older children, this causes easy bruising, bleeding from the nose and excessive wounds, though these symptoms are only seen in cases of severe deficiency.

What causes vitamin K deficiency?

Fortunately, vitamin K deficiency is rare these days due to increased awareness. As discussed, there’s a risk in the first week of life due to poor transport across the placenta. Late VKDB, meanwhile, occurs due to low vitamin K content of breast milk or intestinal malabsorption defects. In infants and older children, low vitamin K levels are seen in cystic fibrosis, severe celiac disease, short bowel syndrome (due to lack of adequate absorptive surface ) and liver disorders.

What are the sources of vitamin K?

Interestingly, there are two main types of vitamin K: the plant-based form, called phylloquinone (vitamin K1), and menaquinones (vitamin K2). The latter refers mostly to bacteria in the gastrointestinal system. Though structurally, they’re subtly different, both serve the same function. The main source of vitamin K1 is green leafy vegetables, such as collards, turnips, spinach, broccoli and natto. Animal-based foods and fermented foods are modest sources of K2.