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Updated 10:00 AM Sept. 18, 2006




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Vitamin K deficiency may be risk factor for osteoporosis

Women, take note. The culprit could be "K."

A new study by a School of Nursing researcher suggests that the impairment of vitamin K function could compromise bone health and contribute to the development of osteoporosis.

Jane Lukacs, assistant research scientist and research fellow, found that one of the early effects of declining estrogen is the impairment of vitamin K function in bone—even before any bone loss that could be attributed to menopause can be measured.

"Our study suggests that the generally accepted level of vitamin K in healthy women is inadequate to maintain bone health just at the onset of menopause," Lukacs says.

Vitamin K is essential for making a bone protein called osteocalcin fully functional. This protein is part of the bone structure when it is "carboxylated" (a chemical modification of the protein that changes its shape, making it easy to bind to calcium) in the presence of sufficient vitamin K. With adequate vitamin K this protein can bind to calcium in the bone environment—somewhat like glue, Lukacs says.

The study involved volunteers of whom 80 percent were white with the remainder of African American, Hispanic and Asian heritage. All were healthy, middle-aged women (approximately 49 years) or young adult women (around 25 years). The study included blood tests, interviews to determine dietary habits, calculation of body mass index and measurements of bone mineral density of the lumbar spine and the "nondominant" hip (i.e. if right-handed, the left hip).

While vitamin K comes from green leafy vegetables, green vegetables and vegetable oils, most people don't consume amounts on a consistent basis sufficient to promote bone health. Few multivitamins contain vitamin K, and those that do have minimal amounts of it. Anyone considering vitamin K supplements should consult with a medical adviser first; people on blood thinners should not take it.

So, what's a woman to do? For now, Lukacs suggests getting back to basics. "In early menopause, increase your intake of dark green vegetables and vegetable oils on a daily basis," she says. "In adolescence and early adulthood, the incorporation of weight-bearing exercise is crucial, because we also observed lower bone density in the hip of premenopausal women in their late 40s well before the onset of menopause.

"Many factors contribute to the development of osteoporosis and fracture risk," Lukacs says. "Part of our effort in this study was to examine vitamin K as a novel nutritional factor that may play a role in bone health in a group of women well characterized for their vitamin nutriture, reproductive status and age, something that is rarely attempted in descriptive studies."

It will be important to explore whether vitamin K supplementation in early postmenopause will offer an additional intervention for women concerned about their future fracture risk, she adds.

Lukacs' study was funded by Pfizer. The findings have been presented at Endocrine Society meetings and are published in the September/October 2006 issue of Menopause.

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