Vitamin K Doesn't Improve Bone Density 10-14-08

Vitamin K supplements do not stop age-related bone loss but may have other benefits for bone health, researchers found.

Bone mineral density continued to drop despite high-dose supplementation in postmenopausal women with osteopenia, reported Angela M. Cheung, M.D., Ph.D., of the University of Toronto, and colleagues in the October issue of PLoS Medicine.

However, clinical fractures were less common among supplement-treated women over four years in the randomized trial (P=0.04), suggesting the vitamin could protect bones through another mechanism, the researchers said.

But it's too early to recommend this strategy clinically, they cautioned.

"Before high-dose vitamin K1 supplementation can be recommended for general use, further randomized controlled trials have to be done to confirm these findings," they said.

Vitamin K -- found mainly in leafy green vegetables -- is best known for its function in the blood coagulation pathway but it is also involved in a chemical reaction essential for the activity of three bone-building proteins.

Low-dose supplements of vitamin K1, also known as phylloquinone, are sold in health food stores and over the Internet as a bone mass booster. K vitamins have also been promoted for cardiovascular health and cancer prevention, the researchers noted.

But because the evidence was conflicting and little was known about long-term effects, the group conducted a randomized, double-blind controlled trial comparing daily oral supplementation with vitamin K1 at a relatively high, 5-mg dose versus placebo.

All 440 postmenopausal women in the study had osteopenia -- indicated by their lowest t-score falling between -1.0 and -2.0 -- and took supplements to reach a total daily intake of 1,500 mg of calcium and 800 IU of vitamin D.

For the primary outcome measure, bone mineral density decreased as much with vitamin K over two years as with placebo at the lumbar spine (-1.28% versus -1.22%, P=0.84) and at the total hip (-0.69% and -0.88%, P=0.51).

Bone mineral density changes were likewise similar through four-year follow-up in the 261 women who entered the long-term extension phase.

Only once in the four-year period was there a significant difference between groups -- a 1.7% difference in femoral neck density at 36 months.

Controlling for compliance, which was generally high, and baseline bone mineral density did not appreciably strengthen the effect of treatment on bone loss.

Differences in measures of bone turnover were not of clinically meaningful magnitudes, the researchers noted, although a drop in serum total osteocalcin levels with vitamin K was statistically significant (21 versus 24 ng/ml, P<0.0001).

Despite the lack of differences in risk markers, clinical fractures were significantly less common among women who took vitamin K than in the placebo group (nine versus 20, hazard ratio 0.41 at two years, P=0.08, and HR 0.45 at four years, P=0.04).

But fragility fractures were not significantly different between groups (six in the vitamin K group versus 11 with placebo, P=0.11).

Adverse events and quality of life were similar between groups overall.

However, fewer vitamin K-treated women developed cancer during the study versus placebo-treated women (3 vs. 12 respectively, HR 0.25, P=0.02).

Lower incidence was also associated with higher mean serum vitamin K levels (P<0.05).

The researchers cautioned that both the cancer and fracture findings could not be ruled out as chance associations, although they are consistent with other research.

Vitamin K was provided by Roche Vitamins (now DSM Nutritional Products), calcium and vitamin D supplements were provided by Whitehall Robbins (currently Wyeth Consumer Healthcare) and Swiss Herbal Remedies.

Comment:

DSM is the worlds largest supplier of bulk vitamins and a very large percentage of the vitamins you buy in health foods stores has at least one of their vitamins in it! The are generally ok, however anything from Wyeth cannot be trusted and that could have effected the study. There are no real studies or evidence anecdotal or otherwise that supports vitamin K promoting bone density.