Data from 200 elderly people showed that high dietary intakes of vitamin K were associated with higher measures of bone mineral density (BMD), and higher scores in an ultrasound test, say findings published in Bone.
“The results of the present study showed, for the first time, a direct association between dietary vitamin K intake and calcaneous quantitative ultrasound measurements, suggesting that vitamin K has a direct role in qualitative bone features along with bone mineral density, in a cohort of elderly Caucasian subjects with healthy dietary habits,” wrote the researchers, led by Monica Bullo from the Human Nutrition Unit at the Universitat Rovira i Virgili in Reus, Spain.
The study adds to the ever-growing body of potential health benefits of vitamin K intakes. Despite the positive impacts, vitamin K deficiency may be more common than previously thought, according to findings from a Dutch study in 2007 (Thrombosis and Haemostasis, Vol. 98, pp. 120-125).
There are two main forms of vitamin K: phylloquinone, also known as phytonadione, (vitamin K1) which is found in green leafy vegetables such as lettuce, broccoli and spinach, and makes up about 90 per cent of the vitamin K in a typical Western diet; and menaquinones (vitamins K2), which make up about 10 per cent of Western vitamin K consumption and can be synthesised in the gut by microflora.
Menaquinones (MK-n: with the n determined by the number of prenyl side chains) can also be found in the diet; MK-4 can be found in animal meat, MK-7, MK-8, and MK-9 are found in fermented food products like cheese, and natto is a rich source of MK-7.
Concerns over deficiency, coupled with increased consumer awareness of the potential benefits, have led to an upsurge in vitamin K formulations as supplements and functional foods. According to Francis Foley from Xsto, the US distributor of Kappa’s K2Vital Vitamin K Product Line, the current K market in the US is valued at $10 million in raw material sales (vs finished product sales). “What is really impressive is the growth in vitamin K supplementation, estimated to be (my personal estimate) over 15 percent year. We feel the K2 market can double to $20 million in less than five years,” he said.
The new Spanish study did not differentiate between the various forms of vitamin K, but looked at overall vitamin K intakes from dietary sources, including greens, dairy, and meat.
A cross-sectional analysis was performed with 200 elderly people with an average age of 67 who completed a 137-item food frequency questionnaire (FFQ) and followed for two years. The researchers used the USDA’s database to estimate vitamin K intakes, and the average intake was calculated to be 334 micrograms per day for men, and 300 micrograms per day for women.
Various measures of bone health, including bone mineral density (BMD), were performed using quantitative ultrasound assessment (QUS) in 125 subjects.
When compared with vitamin K intakes, the researchers report that every 100 microgram increase in vitamin K intake was associated with 0.008 g/m2 increase in BMD, but no other associations were recorded for other bone health markers, added the researchers.
High dietary vitamin K intake was associated with superior bone properties. Moreover, an increase in dietary vitamin K was significantly related to lower losses of bone mineral density and smaller increases in the porosity and elasticity attributed to aging, which helps to explain the previously described protective effect of vitamin K intake against osteoporotic fractures.
“The subjects in our study generally consumed a healthy diet means that the effect of an increase in dietary vitamin K intake may be masked and that in populations with lower consumptions of vitamin K or poor nutrition an increase would be much more beneficial,” added the researchers.
There is biological plausibility for the potential bone health benefits of vitamin K. Osteocalcin is a vitamin K-dependent protein and is essential for the body to utilise calcium in bone tissue. Without adequate vitamin K, the osteocalcin remains inactive, and thus not effective.
Published online ahead of print, doi: 10.1016/j.bone.2011.03.767
“Dietary vitamin K intake is associated with bone quantitative ultrasound measurements but not with bone peripheral biochemical markers in elderly men and women”
Authors: M. Bullo, R. Estruch, J. Salas-Salvado