1. ¹Menzies Centre for Population Health Research, Hobart, Tasmania, Australia
2. ²Department of Epidemiology and Preventive Medicine, Monash University, The Alfred Hospital, Prahran, Victoria, Australia
3. ³Diabetes and Endocrine Services, Royal Hobart Hospital, Hobart, Tasmania

Correspondence: G Jones, Menzies Centre for Population Health Research, GPO Box 252-23, Hobart, Tasmania 7000, Australia. E-mail: g.jones@utas.edu.au

^*Guarantor: G Jones.

^†Contributors: GJ was responsible for study conception, data analysis and overall manuscript composition. TD and TMG were responsible for study conception and manuscript review. KH was responsible for data collection and manuscript review. FS was responsible for phytoestrogen assays and manuscript review. VP was responsible for bone assays and manuscript review.

Received 1 November 2001; Revised 15 May 2002; Accepted 28 May 2002.

Abstract

Objective: To assess the effect of phytoestrogens on bone turnover and growth in adolescent boys.

Design: Randomized double-blind placebo-controlled trial.

Setting: Single school in northwest Tasmania.

Participants: Adolescent boys (treatment n=69, placebo n=59, mean age 16.8 y).

Interventions: Six weeks of isoflavone supplementation (Novasoy, 50 mg daily of isoflavone equivalents). Bone turnover markers (bone specific alkaline phosphatase (BAP) and pyridinoline creatinine ratio (PYR)) were measured at baseline and follow-up.

Results: Despite marked increases in urinary genistein and daidzein in the treatment arm (both P<0.001), there were no significant differences in BAP, PYR or short-term height or weight change. This applied to both intention-to-treat and per protocol analysis. Neither was there a significant correlation between urinary genistein and daidzein levels and BAP or PYR.

Conclusions: Phytoestrogen supplementation to the level of usual Japanese dietary intake has no measurable effect on bone turnover in adolescent boys. Longer-term studies of bone density may be desirable but it is unlikely that there will be a large effect in either girls or boys given the lower endogenous oestrogen levels in boys.

Sponsorship: National Health and Medical Research Council of Australia, Arthritis Foundation of Australia.