Vitamin K2 Supplementation May Slow Bone Loss in AN

Decreased bone mineral density (BMD) is one of the more serious complications of anorexia nervosa (AN). Weight recovery and resumption of menses may take a prolonged period, during which bone loss can continue. Japanese researchers recently reported that use of vitamin K2 supplements might help reduce BMD loss in AN patients (Psychiatry Res 2003; 117:259).

Vitamin K is essential for the carboxylation of osteocalcin, a protein produced by osteoblasts (bone-producing cells) and used as an integral process of bone formation. Vitamin K has also been shown to inhibit the natural cell death of, and maintain the number of, osteoblasts. Although both vitamin D and vitamin K are important for bone growth, vitamin K may be more effective. Women with low vitamin K levels but high vitamin D intakes have been shown to have a greater risk of hip fracture than women with high vitamin K and low vitamin D intakes (Curr Opin Clin Nutr Metab Care 2001; 4:483)

A soy product studied for more than a century

Vitamin K1 is commonly found in dark green plants such as lettuce and spinach, while vitamin K2 is found in fermented foods such as blue cheese and natto, a common dish in Japan. Natto is a fermented soy product and contains a significant amount of food-based K2, which seems to be better absorbed than vitamin K1. Circulating K2 levels measured after consumption of natto have been shown to be about 10 times higher than those of vitamin K1 after eating spinach. For more than 100 years, Japanese researchers have studied natto and its effects on osteoporosis. The current RDA of vitamin K is 1 mcg/kg; a dosage of 1-5 mg daily (1000-5000 mcg) would approximate the levels seen in Japanese women who regularly eat natto or fermented foods and dark green vegetables.

The current study: vitamin K2 helped maintain BMD

Dr. T. Iketani and colleagues from Osaka City University Medical School conducted a nonrandomized one-year follow-up study of the effects of menatetrenone (vitamin K2) on bone loss in 10 AN patients who received K2 treatment and 11 patients who did not. Bone mineral density among the K2-treated group decreased significantly less than that of those who did not receive vitamin K2 (-2.8% and –6.9%, respectively). Lumbar bone mineral density was measured with dual energy x-ray absorptiometry.

The authors report that their results suggest that menatetrenone may be beneficial in preventing bone loss in patients with AN. Dr. Neil Binkley and colleagues at the University of Wisconsin Medical School, Madison, are comparing vitamin K1 and K2 and placebo in postmenopausal women with normal bone density. Their hope is that they will find a low-cost, side-effect-free approach to preventing osteoporosis.

(Note: The response to vitamin K probably depends on the baseline status of the patient. Most AN patients have a large intake of vitamin K from vegetables. If their vitamin K status is sufficient, giving them more, through supplements or other foods, should not be expected to have any effect on bone density.)