Got Greens? Your bones certainly hope so. In addition to being a good source of calcium, dark greens provide a steady stream of nutrients needed to put calcium to work, including vitamin K. While vitamin K was originally thought to be involved just with blood coagulation, researchers recently discovered that the body uses it to activate osteocalcin and other bone proteins needed to prevent osteoporosis. In fact, those that consume more dietary vitamin K have a lower hip fracture risk.
In one large, long-term study, women consuming over 109 micrograms of dietary vitamin K (see table below) each day had a 30% lower risk of hip fracture than those consuming less than 109 micrograms.[i]
There are two main types of this fat-soluble vitamin: K1 (phytonadione) is predominantly found in leafy green vegetables, such as kale, collards, spinach, mustard greens, and broccoli, and K2 (menaquinone) is found in meat and cheeses and manufactured by bacteria in the colon. Long-term antibiotic usage may reduce vitamin K levels by destroying intestinal bacteria. If you’re taking antibiotics, eat yogurt and other living fermented foods with active cultures and keep eating green leafy vegetables.
Vitamin K got its name for the role it plays in blood clotting (Koagulation is the German word for coagulation). Those that are taking the anticoagulant Coumadin have been told to drastically reduce vitamin K levels so the medication will work effectively. This is unfortunate. A better option is to ask your physician to adjust Coumadin levels to accommodate a higher intake of vitamin K so that you can get the many valuable nutrients in greens. If you choose this route, you’ll need to be consistent with your daily intake of vitamin K.
Food (1 cup cooked)
Lettuce (green), raw
Large observational studies DO NOT positively correlate milk intake with a reduced hip fracture rate. Surprising, isn’t it? Healthy bones require activity, calcium, vitamin D, magnesium, vitamin K, folate, and an array of other plant nutrients. Because greens contain many of these nutrients, I believe that they, and not cheese, milk, yogurt, or ice cream, are one of the keys to keeping bones healthy. Two-thirds of the people in the world maintain healthy bones without eating any dairy products at all.
There is some evidence that those who consume more vitamin K have a lower heart disease risk. Exactly why is not clear. A low vitamin K intake may accelerate arterial calcification. Some researchers think that a substantial part of the population is mildly deficient in vitamin K, and at later ages this deficiency may contribute to increased bone fracture risk, arterial calcification, and cardiovascular disease.[ii]
What to Do: Eat greens more often and when you do, eat more of them. When cooking dinner, prepare larger quantities so that you can have leftovers for lunch the next day. Try Popeye’s Collards if you haven’t already.
- Greg Hottinger, MPH, RD
[i] Feskanich D, et al. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr. 1999 Jan;69(1):74-9.
[ii] Vermeer C, Schurgers LJ. A comprehensive review of vitamin K and vitamin K antagonists. Hematol Oncol Clin North Am. 2000 Apr;14(2):339-53.