What is the clinical evidence that cruciferous vegetables and the supplemental compounds 3,3’ diindolylmethane, sulforaphane and indole-3-carbinol, modulate the potentially harmful effects of oestrogen metabolites? A narrative review

By Rebecca Wakefield - Nutrition Science and Practice

Abstract

Background

The homeostasis of oestrogen metabolism plays an important role in human health. Various factors may influence enzyme activity across both phases of oestrogen metabolism. These include diet, environment, lifestyle, and genetic polymorphisms. Cruciferous vegetable compounds have been shown in vitro to modulate enzyme activity, but clinical studies are limited.

Aim

To conduct a narrative review of the current clinical evidence on the role of cruciferous vegetable intake as a whole food or as the supplemental compounds sulforaphane, indole-3-carbinol and 3,3 diindolylmethane and their effectiveness and appropriateness in supporting the production of safer oestrogen metabolites.

Methodology

A narrative review was undertaken consisting of a systematic search of biomedical databases and online journals. Key search terms were identified using the PICOS framework. Only quantitative, clinical studies that included the measurement of oestrogen metabolites were selected. Critical appraisal of study quality and data extraction of key points preceded a narrative synthesis of the results.

Findings

Initial searches resulted in a total of 513 papers. Duplications and non-clinical trials were removed leaving 94 full-text papers. After the inclusion and exclusion criteria were applied, six papers were included. An additional paper was included from the Cochrane central register of controlled trials. Studies included three indole-3-carbinol intervention studies and four 3,3’ diindolylmethane intervention studies. Indole-3-carbinol significantly increased the 2:16α-OHE1/2 ratio at doses ranging from 200-800mg. DIM only had a significant effect on the ratio at doses of 300mg using liquid chromatography-mass spectrometry or 400mg using the immunoassay. No serious adverse effects were reported for either intervention.

Conclusion

Interpretation of the findings is limited by the significant heterogeneity of the included studies and the overall poor quality of study design and reporting. Studies did not include whole foods or sulforaphane and only phase one oestrogen metabolites were measured, therefore providing an incomplete picture of the clinical role of cruciferous vegetables and their compounds on human health.