Of all the lettered vitamins, vitamin K is perhaps the least talked about. But that’s beginning to change, as ample research over the past few decades has thrust this vital nutrient into the spotlight. 

Vitamin K’s best-known function is its role in normal, healthy blood clotting. In fact, “K” comes from the German word koagulation. While we may not think of coagulation as an essential body function, we couldn’t live without it—we’d literally bleed to death. 

Researchers began to recognize vitamin K’s role in blood clotting thanks in part to studies surrounding the blood-thinning medication warfarin, commercially known as Coumadin. Prescribed to people prone to blood clots, warfarin works by disrupting vitamin K’s activity and stopping the body from recycling it for continual clotting. In fact, in these cases, when clotting could block blood flow to the brain or heart and trigger a stroke or heart attack, excess vitamin K can counteract warfarin’s anticlotting effects. But if clotting isn’t an imminent threat, vitamin K is key.

The vitamin’s benefits go beyond blood clotting, though. Another chief function is its unique ability to shuttle calcium from the arteries and deposit it into the bones. This yields a two-pronged bonus: It helps prevent calcification—or hardening—of the arteries, a risk factor for heart disease, and it provides bones with a critical building block. 

A study of 4,800 participants published in the Journal of Nutrition in 2004 linked higher vitamin K intakes to decreased risk of coronary heart disease and lower overall mortality rates. As for bones, along with putting calcium in the right spot, vitamin K also sparks a particular protein into action that allows bones to use calcium correctly for continued regeneration. According to a research review published in the journal Nutrition in 2001, vitamin K increases bone mineral density in people with osteoporosis and also reduces fracture risk. Vitamins K and D are thought to work synergistically to further bolster bone health.

According to the Linus Pauling Institute, our bodies use up vitamin K rapidly and store very little of it, so reserves are easily depleted without sufficient intake. To prevent deficiency, our ever-wise bodies continuously recycle the vitamin, allowing it to be used again and again, in turn decreasing the dietary requirement. Therefore, all-out deficiency—marked by bleeding gums, blood in the urine, chronic nosebleeds or excess bruising—is rare. 

Still, health experts say Americans take in less vitamin K than we did before the typical diet shifted from plant-based foods and grass-fed meat sources toward processed fare. They contend that many of us could use more vitamin K. According to the National Institutes of Health, good food sources include leafy greens like lettuce, spinach, Swiss chard, kale and collards, as well as broccoli, Brussels sprouts, cabbage and cauliflower. Olive, soybean and canola oils, as well as fish, eggs and some cereals, contain lesser amounts of vitamin K.

All benefits considered, K might be the last vitamin alphabetically, but it’s no less important than A, B, C, D or E.