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Vitamin K has long been known to play an important role in blood clotting. Recent research has focused on the influence of vitamin K in diseases such as heart disease, osteoporosis, diabetes and cancer. But let’s focus here on bone health.
“There is scientific rationale for looking at the association between vitamin K, bone density and fracture risk,” says rheumatologist Chad Deal, MD. Vitamin K activates proteins involved in bone formation and mineralization (a process that makes bones strong).
Vitamin K comes in two forms — K1 and K2. Vitamin K1 is found primarily in green, leafy and cruciferous vegetables. Vitamin K2, which is predominantly produced by bacteria, is further divided into subgroups named MK4 to MK13. Foods rich in vitamin K2 include some dairy products, pork, poultry and fermented foods.
Vitamin K2 may have more of a protective effect on bone than vitamin K1. However, deficiencies of both K1 and K2 appear to have a negative effect.
Several observational studies have found that inadequate intake of vitamin K is linked to low bone density and increased risk for fractures.
A study that analyzed data from the large Nurses’ Health Study found that women who consumed less than 109 micrograms (mcg) of vitamin K per day were more likely to break a hip.
A study of participants (both men and women) in the large Framingham Heart Study also showed a link between low vitamin K intake and increased risk of hip fractures. This study also showed an association between low dietary intake of vitamin K and low bone density in women.
An adequate intake of vitamin K is considered to be 120 mcg for men and 90 mcg for women. A true vitamin K deficiency, which is marked by an inability of blood to clot normally and easy bruising, is rare. “Most people can avoid a deficiency by getting enough vitamin K in their diet,” says Dr. Deal.
Based on the connection between vitamin K and bone health, several studies looked at whether it makes sense for anyone, including people with osteoporosis or at risk for it, to take vitamin K supplements. So far, results have been mixed.
Some studies, many of them conducted in Japan, found that supplementation with vitamin K1 or vitamin K2 improved bone mineral density, and few studies showed a decreased risk of bone fractures. Some subsequent studies found that vitamin K supplementation had no effect on bone mineral density. Many of the studies conducted thus far are limited by flaws in the design or a small number of participants.
Evidence to support vitamin K supplementation is too preliminary and contradictory to make recommendations. The U.S. Food and Drug Administration has not authorized a health claim.
“There is evidence for some positive effect, and there are ongoing studies,” says Dr. Deal.
Vitamin K supplements are relatively safe, and many people take them. People taking blood-thinning drugs, such as warfarin (Coumadin®), should not take vitamin K without consulting their doctor because vitamin K can reverse the effects of these drugs.
This article originally appeared in Cleveland Clinic Arthritis Advisor.