The influence of a low-boron diet and boron supplementation on bone, major mineral and sex steroid metabolism in postmenopausal women.

An increase in dietary intake of B from 0.25 to 3.25 mg/d has been reported to increase plasma oestradiol and testosterone and decrease urinary Ca excretion in postmenopausal women. Consequently, it is suggested that the higher level of B intake could reduce bone loss associated with the menopause and cessation of ovarian function. The present study was designed to investigate the effect of a B supplement on bone mineral absorption and excretion, plasma sex steroid levels and urinary excretion of pyridinium crosslink markers of bone turnover in healthy postmenopausal volunteers. The women were accommodated in a metabolic unit, given a low-B diet (LBD; 0.33 mg/d) for 3 weeks and were asked to take a B supplement of 3 mg/d in addition to the LBD for a further 3 weeks. Changing B intake from 0.33 to 3.33 mg/d had no effect on minerals, steroids or crosslinks. However, the LBD appeared to induce hyperabsorption of Ca since positive Ca balances were found in combination with elevated urinary Ca excretion. This phenomenon may have inhibited or obscured any effect of B.