Vitamin K Intake Important in the Prevention of Osteoporosis

James Meschino DC, MS, ROHP

 A recent study published in the American Journal Of Clinical Nutrition (2003, vol. 77, No. 2: 512-516) has provided additional evidence that Vitamin K intake is an important determinant of bone mineral density and risk of risk of hip fractures. In a study conducted at the Jean Meyer USDA Human Nutrition Research Center, researchers assessed Vitamin K intake of 1,479 women and 1,112 men, aged 29-86, who had participated in the Framingham Heart Study.  The results showed that women in the lowest quartile of Vitamin K intake had significantly lower hip and spine bone mineral density (BMD) than those women in the highest quartile.  There was no association between Vitamin K intake and BMD in men, however. Researchers concluded that the results were consistent with previous reports that low dietary Vitamin K intake is associated with an increased risk of hip fracture in women.

Vitamin K is required for the synthesis of osteocalcin, an important protein that forms part of the bone matrix. A lack of osteocalcin has been shown to weaken bone and predispose individuals to osteoporosis and bone fractures.  Thus, a biochemical basis exists to explain how a sub-optimal intake of Vitamin K can predispose an individual to the development of osteoporosis and related fractures.

In one study of 71 postmenopausal women, participants with reduced bone mineral density showed lower serum levels of Vitamin K, than those with normal bone density. Similar results have been seen in other studies as well.  A recent report from the Nurses’ Health Study involving 12,700 participants found that higher dietary intake of Vitamin K was associated with a significantly reduced risk of hip fracture.

The official U.S. recommendations for daily intake of Vitamin K for adult women is 75 mcg per day, however, studies now suggest that an intake in the range of 110 mcg per day may be required to help reduce risk of osteoporosis in women. The current RDA for adult men is set at 120 mcg per day.

Vitamin K is found naturally in green leafy vegetables, including kale, turnips, spinach, broccoli, lettuce, and cabbage.  Green tea is also a good source. Other food items contain respectable levels as well, such as oats, green peas, whole wheat bread, green beans, watercress and asparagus.

Of note is the fact that Vitamin K is also synthesized by the bacteria in the large intestine (gut flora), and represents a significant contribution to an individual’s Vitamin K nutritional status.

The most well known function of Vitamin K in the body involves its participation in blood clotting. In fact, the blood-thinning effect of warfarin (Coumadin) works by antagonizing the effects of Vitamin K.  Conversely, Vitamin K supplements, or intake of foods rich in Vitamin K, block the action of these blood-thinners, and this must be considered in patients using these medications (requires monitoring of the INR).

In summary, a number of recent investigations implicate sub-optimal intake and/or serum levels of Vitamin K in the development of osteoporosis. In addition to its role in blood-clotting (pro-coagulant), Vitamin K is less appreciated for its vital role in the synthesis of osteocalcin, an important bone protein.  Thus, health practitioners should encourage patients to derive adequate amounts of Vitamin K from food sources and determine if Vitamin K supplementation may be of further value on a case-by case basis, factoring in whether or not the patient is taking the blood-thinner warfarin, which is a contraindication to the indiscriminate use of Vitamin K supplements (including Vitamin K contained within a multiple vitamin and mineral supplement).

References:

1. NNFA Supplement – Mon, March 31, 2003
2. com (Vitamin K)