You may never have heard of vitamin K before, but a new study shows that if you want to ward off osteoporosis, you'll want to make sure you're getting enough.

A new metanalysis (a statistical review of several studies) of seven Japanese clinical trials found that patients, the majority of them elderly women, taking either 15 or 45 mg daily of a synthetic form of vitamin K (known as MK-4) showed a 77 percent reduction in hip fractures, a 60 percent reduction in vertebral fractures, and an 81 percent reduction in all nonvertebral fractures (Archives of Internal Medicine, 2006, vol. 166, no. 12).

At least three proteins in bone depend on vitamin K to aid in the calcium-binding process known as mineralization. "That's reason enough to make sure your diet is adequate in vitamin K," said Chad Deal, MD, who runs the Center for Osteoporosis and Metabolic Bone Disease at the Cleveland Clinic Foundation.

Good dietary sources of vitamin K include dark green leafy vegetables like spinach, broccoli, and collard greens. (It has not yet been established how much vitamin K-rich food a person needs to reap benefits similar to that of study participants (who took relatively high doses of synthetic vitamin K) but the findings clearly are yet another reason to eat your five-plus daily servings of veggies.)

Approximately 10 million Americans, 80 percent of them women, have osteoporosis. Another 34 million are at risk of developing the disease due to low bone density. Osteoporosis is responsible for more than 1.5 million fractures every year.