"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 said.
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---sort of like glue, Lukacs said.
The study involved volunteer human subjects of whom 80 percent were white with the remainder of African-American, Hispanic and Asian heritage. All were healthy middle-aged women or young adult women. The study included blood tests, interviews to determine dietary habits and calculation of the body mass index and measurement of bone mineral density of the lumbar spine and the non-dominant hip. If right handed, left hip.
While vitamin K comes from green leafy vegetables, green vegetables and vegetable oils, most individuals don't consume amounts on a consistent basis that are sufficient to promote bone health. Few multivitamins contain vitamin K, and those that do have minimal amounts of vitamin K. Anyone considering vitamin K supplements should consult with their medical adviser first; people on blood thinners should not be taking vitamin K.
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 said. "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 40's well before the onset of menopause.
"Many factors contribute to the development of osteoporosis and fracture risk," Lukacs said. "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."
She said it will be important to explore whether vitamin K supplementation in the early postmenopause will offer an additional intervention for women concerned about their future risk of fracture.
Lukacs's study was funded by Pfizer. Her findings have been presented at the Endocrine Society meetings and are published in the September/October 2006 issue of Menopause (volume 13, issue 5.)
U-M School of Nursing: http://www.nursing.umich.edu/