Effects of vitamin E on bone turnover markers among US postmenopausal women

Abstract

Increased oxidative stress and inflammation resulting from aging and declining estrogen levels can lead to increased bone loss in postmenopausal women. Alpha-tocopherol and gamma-tocopherol, the two predominant isomers of vitamin E, have antioxidant and anti-inflammatory properties, but their effects on bone metabolism have not been well studied in humans. We examined the associations between dietary and total (diet and supplements) alpha-tocopherol intake, serum alpha-tocopherol and gamma-tocopherol levels and their ratio, and bone turnover markers (BTMs) among postmenopausal women aged ≥45 years. We used cross-sectional data from the National Health and Nutrition Examination Survey 1999–2002. Multiple regression models with adjustments for relevant confounders were used to examine the associations between intake and serum levels of tocopherols, and serum bone-specific alkaline phosphatase (BAP), a biomarker of bone formation, and urinary N-telopeptides/creatinine (uNTx/Cr), a biomarker of bone resorption. The study sample included 497 postmenopausal women who were not taking estrogen, steroids, or osteoporosis medications, were free from kidney and liver disease, cancer, and rheumatoid arthritis, and were fasting >9 hours prior to examination. Participants had a mean age of 65.5 ± 0.6 years and over 45% used vitamin E (alpha-tocopherol) supplements in the past month. Vitamin E supplement users had significantly lower serum gamma-tocopherol, higher serum alpha-tocopherol levels, and higher ratio of serum alpha-tocopherol to gamma-tocopherol than nonusers. High serum gamma-tocopherol levels and low ratio of serum alpha-tocopherol to gamma-tocopherol were associated with increased BAP levels (p < 0.01 for both). There were no associations between any of the vitamin E variables and uNTx/Cr. In conclusion, we hypothesize that gamma-tocopherol may uncouple bone turnover, resulting in more bone formation than resorption. Vitamin E supplements in the form of alpha-tocopherol suppress serum gamma-tocopherol levels and may have negative effects on bone formation. Further research is needed to investigate the potential anabolic effect of gamma-tocopherol from food sources on bone.