Tuesday, July 31, 2012

Vitamin E: Bone Formation

Oxidative stress and the rampant production of pro-inflammatory cytokines are major causes of chronic disease--including osteoporosis. When estrogen levels decline at menopause there is a sharp rise in free radicals in a women's body. Radicals such as reactive oxygen species (ROS) evoke the excessive production of signaling molecules called pro-inflammatory cytokines. These molecules, when produced in excess during oxidative stress, stimulate aggressive osteoclastic, bone destroying, activity. The result is rapid bone loss, and eventually osteoporosis. You would think, therefore, that any and all nutrients with antioxidant activity, especially the powerful antioxidant vitamin E, would be beneficial to individuals with osteoporosis. Oddly, there have been very few studies looking at the association between vitamin E and bone loss and the only major study (Wolf et al., 2005) to at least partially look at tocopherols, found no association between vitamin E intake and bone mineral density (BMD). This substudy, unfortunately, only looked at the benefits of short-term vitamin E intake on bone mineral density. (Dietary effects on bone density occur over the long-term.) Laboratory bone turnover markers (BTMs), on the other hand, have been shown to better reflect the dietary (or supplemental) effects on bone metabolism.

This superior method (BTMs vs BMD) of analyzing the effects of diet and supplements on bone was used in a recent study published in the Journal of Bone and Mineral Research (Hamidi et al., 2012). The authors examined the association between vitamin E intake and BTMs in postmenopausal women.

Alpha-tocopherol and gamma-tocopherol are the two predominant forms of vitamin E. Alpha-tocopherol (found in nuts, seeds, oils, whole grains, leafy green vegetables, etc) is a better antioxidant, while gamma-tocopherol (soybeans, corn, canola oil, seeds, and nuts) has better anti-inflammatory properties. 

The study found "a significant positive association between serum gamma-tocopherol, and a significant negative association between the serum ratio of alpha-tocopherol to gamma-tocopherol and BAP" (bone-specific alkaline phosphatase), a marker for bone formation. "There were no associations between any of the vitamin E variables and uNTx/Cr levels." (NTX is a bone resorption biomarker that reflects osteoclastic bone resorption activity.)

The study also found that "high doses of vitamin E supplements suppressed serum gamma-tocopherol levels" and "high serum alpha-tocopherol to gamma-tocopherol ratio was associated with  low BAP levels." [i.e. lower bone formation] The authors "hypothesize that gamma-tocopherol may uncouple bone turnover, resulting in increased bone formation without affecting bone resorption. Vitamin E supplements in the form of alpha-tocopherol suppress serum gamma-tocopherol levels and may have negative impact on bone formation."

Wolf RL et al. 2005. Lack of a relation between vitamin and mineral antioxidants and bone mineral density: Results from the Women's Health Initiative. Am J Clin Nutri 82:581-588.

Hamidi, M.S., Corey, P.N. and Cheung, A.M. 2012. Effects of vitamin E on bone turnover markers among US postmenopausal women. JBMR 94(4):1063-1070.
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