The University of Michigan School of Nursing study found that typical intake of vitamin K may in fact not be enough to support bone health in the perimenopausal years.
The finding could spur formulators to more actively promote vitamin K for pre-menopausal women, although the ingredient can cause complications for those on blood thinners.
Vitamin K is found in green and green leafy vegetables as well as vegetable oils, however most individuals do not consume sufficient amounts to promote bone health. Few multivitamins contain vitamin K, and those that do have minimal amounts of the nutrient.
According to lead author Jane Lukacs, the current intake is recommended to be 1 ug/kg/d, based on Vitamin K's influence on blood clotting.
"What is becoming apparent, is that what is adequate for blood clotting may not be adequate for bone health," said Lukacs .
In the UK, the average age at which women reach menopause is 51 years, according to the National Osteoporosis Society. Menopause is characterized by a loss of oestrogen production, which accelerates bone loss. At worst, this can lead to osteoporosis, a disease characterized by brittle bones.
The study, published in the current issue of the journal Menopause (13(5):799-808, September/October 2006), noted that one of the early effects of declining oestrogen is the impairment of vitamin K function in bones even before bone loss from menopause can be measured.
Fifty-nine healthy women participated in the study funded by pharmaceutical giant Pfizer. The women were divided into three groups: 19 women aged 40-52; 21 women aged 20-30; and 19 untreated women between 40-52 years.
The study included blood tests, interviews and food frequency quesionnaires to determine dietary habits, calculation of the body mass index as well as measurement of bone mineral density of the lumbar spine and the non-dominant hip.
"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," said lead author Jane Lukacs, she did not express an opinion on optimum vitamin K intake.
With the help of vitamin K, the protein osteocalcin can bind to calcium in the bone. This protein becomes part of the bone structure when it is chemically modified to bind to calcium through a carboxylization.
In the study, the percentage of undercarboxylated osteocalcin was higher in the untreated early postmenopause cohort compared with all the other women (21.9+/-1.7 percent vs 17.4+/-0.9 percent, n=40; P = 0.02). This implies these women were deficient in vitamin K.
"Percentage of undercarboxylated osteocalcin may be a specific bone marker of the early postmenopause in healthy women," concluded the study.
Lukacs said it is necessary to explore whether vitamin K supplementation in the early postmenopause will offer an additional intervention for women concerned about their future risk of fracture.
Those who take anticoagulant medicine for hypercoagulation however are generally advised not to take vitamin K because it is thought to play a role in blood clotting.