Using food as a vitamin K supplement

The study, published in Calcified Tissue International, included 173 healthy postmenopausal women without osteoporosis. They were divided into four groups: the control group ate their usual diet and received no supplements; the other three groups received diet and exercise counselling, and were given milk and yoghurt products fortified to provide 800 mg of calcium and 10 mcg (400 IU) of vitamin D3 per day for one year. In addition, 100 mcg of vitamin K1 (phylloquinone) was added to the dairy products of one group and 100 mcg of vitamin K2 (menaquinone-7) was added to the dairy products of another group. Bone density and blood and urine markers of bone turnover (breakdown and repair) were measured at the beginning and end of the study.

Vitamin K key to protecting bone

A few significant differences between the groups were identified at the end of the study:

• All three groups of women eating fortified dairy foods gained bone mineral density during the study, but in the control group, bone mineral density decreased.
• Only the women receiving vitamin K1 or K2 had an increase in bone density in the lower spine.
• Both of the vitamin K groups also had lower levels of blood and urine markers for bone turnover at the end of the study than women in the control and calcium-plus-D groups.

“The present study revealed more favourable changes in bone metabolism and bone mass indices for the two vitamin K supplemented groups,” the study’s authors said.

K1 and K2: two sides of one vitamin

Scientists used to think vitamin K was only important because of its role in blood clotting. Now vitamin K is attributed with heart-protective and bone-preserving actions. The form of vitamin K known as phylloquinone, or K1, is the most abundant form in plants and is believed to play the biggest role in blood clotting; K2 refers to a group of related types of vitamin K known as menaquinones that are thought to be more involved in the other effects of vitamin K.

Getting more K from food

This study showed that a comprehensive osteoporosis-prevention programme is more effective if it includes vitamin K. Here are some ways to increase your intake:

• Eat your greens. Green leafy vegetables are a major source of vitamin K1, and adding a drizzle of oil makes this fat-soluble vitamin more absorbable.
• Enjoy an egg. A type of vitamin K2 known as menaquinone-4 is made from K1 by certain tissues in the body. In addition, eggs and hard cheeses are good food sources of K2.
• Get to know natto. Healthy bacteria in the intestines produce some of the type of vitamin K2 used in this study, menaquinone-7. Natto, a traditional Japanese fermented soya food, is rich in this form of K2, as are other fermented foods like sauerkraut, yoghurt, and kefir.

(Calcif Tissue Int 2012;90:251–62)