“Vitamin K2 is crucial for osteoporosis prevention,” claims Mercola.com (which will be happy to sell you a 30-day supply of K2 for $28).

“There are 11 forms of vitamin K,” says Sarah Booth, director of the Vitamin K Laboratory and of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

Leafy greens are good sources of K1. The other 10 forms, collectively called K2, are made by bacteria.

“We like to refer to a K2-rich diet as the Oktoberfest Diet,” says Booth. “Cheese, cured meat, sauerkraut. And natto”—fermented soybeans—“is also loaded with K2.”

Is vitamin K essential for healthy bones?

“Multiple proteins in bone require vitamin K,” Booth explains. But when researchers randomly assigned people to take vitamin K1 or a placebo, most saw no effect on markers like bone density or bone loss. “Multiple trials, including at our center, came up empty,” says Booth.

Is vitamin K2 different?

Roughly 15 years ago, several Japanese studies reported a lower fracture risk in people given huge doses of K2—45,000 micrograms a day. (The recommended daily intake is 120 micrograms for all forms of vitamin K combined.)

What about lower doses of vitamin K2?

Newer trials testing lower doses of K2 have found either small or no benefits.

For example, in one company-funded study, researchers assigned roughly 220 postmenopausal Dutch women to take a placebo or 180 micrograms a day of K2.

After three years, the placebo takers had lost more bone mineral (3 percent) than the K2 takers (2 percent) at the site where most hip fractures occur. While the difference was statistically significant, “I wouldn’t get too excited about it until other teams replicate those findings,” says Booth.

The bottom line

“Right now, there is no evidence to support anyone taking vitamin K supplements for bone health,” says Booth. “You can easily get all forms of vitamin K from a healthy diet.”

Photo: © maglara/stock.adobe.com.