Stephen Roberts and Dr. Robert Davidson, Nutrition Department
Vitamin K, long established as important for blood clotting, has received more recent attention regarding a role in bone metabolism and remodeling.1 Vitamin K could potentially be an effective treatment in reducing the deleterious effect of osteoporosis.
Osteoporosis is a disease characterized by increased bone loss, lower bone density, and increase in the incidence of fractures. Post-menopausal females are one group that is significantly at risk for developing osteoporosis.
Ovariectomized (OVX) rats (rats that have surgically had their ovaries removed) are a widely accepted animal model for bone loss in post-menopausal human females. Previous research has shown that both omega-3 and vitamin K supplementation can affect the rate of bone loss. 2,3,4 The finding that vitamin K supplementation reduces the rate of bone loss in OVX rats was challenged in at least one other study. 5
We did an animal study to investigate this. One of the project goals included determining whether vitamin K supplementation independently reduces bone loss or if it must work in conjunction with other compounds (specifically Omega-3) to have any effect. Another goal was to test our hypothesis that simultaneous vitamin K supplementation and high levels of omega-3 in the diet will have an additive effect with respect to bone preservation. It should be noted that pharmacological levels of vitamin K were administered (1500x the current recommended daily allowance—there is currently no upper limit on vitamin K intake).
For this study we divided the rats into five groups of eleven and fed them different dietary regimens over a period of eight months. The first group underwent sham surgeries (in which surgery is performed but ovaries are not removed) and all other rats were ovariectomized. The rats were separated into the following dietary groups:
Every eight weeks the rats were scanned using DXA (Dual Energy X-Ray Absorptiometry) to measure bone mass density (BMD). Imaging focused on two areas—the distal femur (knee) and the femur diaphysis (bone shaft) including the distal region.
Results showed that the density of the diaphyses measured in OVX rats fed diets high in omega-3 fats and independent vitamin K was significantly higher than OVX rats fed a regular diet (control) after eight months. However, the OVX rats fed a diet both high in omega-3 and supplemented with vitamin K were not significantly higher than the control rats (in fact, the trend shows that it may be lower). Furthermore, we observed different responses to treatments depending on the bone region. In the knee measurements, the SHAM group was not significantly denser than the control which indicates that when using the Ovariectomized Rat Model, knee densities are not a good indicator of bone loss.
We presented our findings via a conference poster at the Experimental Biology Conference in Washington D.C. which was held from April 28 – May 2, 2007. We were able to inform other researchers and get answers to questions that arose during our research. We intend to incorporate this data into part of a larger study that we will present to the Journal of Nutrition for publication.
WORK CITED
- Suttie J. Modern Nutrition in Health and Disease. 10th ed. Philadelphia: Lippincott Williams & Wilkins; 2001.
- Watkins B., Li Y., Seifert M. Dietary ration of n-6/n-3 PUFAs and docosahexaenoic acid: actions on bone mineral and serum biomarkers in ovariectomized rats. J Nutr Biochem 17:282-289; 2006.
- Akiyami Y., Hara K., Ohkawa I., and Tajima T. Effects of menatetrenone on bone loss induced by ovariectomy in rats. Jpn J Pharmacol 62:145-153; 1993.
- Shiraishi A., Higashi S., Masaki T., Saito M., Ito M., Ikeda S., Nakamura T. A Comparison of Alfacalcidol and Menatetrenone for the Treatment of Bone Loss in an Ovariectomized Rat Model of Osteoporosis. Calcif Tissue Int 71:69-79; 2002.
- Binkley N., Krueger D., Engelke J., Crenshaw T., Suttie J. Vitamin K Supplementation Does Not Affect Ovariectomy-induced Bone Loss in Rats. Bone 30:897-900; 2002.