Effect of diindolylmethane supplementation on low-grade cervical cytological abnormalities: double-blind, randomised, controlled trial

BACKGROUND: Cervical screening identifies many women with low-grade abnormalities. In vitro and in vivo studies have shown that diindolylmethane (DIM) could potentially halt (cervical) carcinogenesis. We report on a randomised controlled trial of the effect of DIM in women with low-grade cervical cytological abnormalities. METHODS: We conducted a pragmatic double-blind, randomised controlled trial of 150 mg DIM (from BioResponse DIM) or placebo daily for 6 months in women with newly diagnosed, low-grade cytological abnormalities. Randomisation was in the ratio 2 (DIM) to 1 (placebo). All women were invited for colposcopy at 6 months with biopsy of any abnormality. RESULTS: Of the 551 randomised women available for analysis, 9% on DIM and 12% on placebo had cervical intraepithelial neoplasia-2 (CIN2) or worse after 6-month supplementation (risk ratio (RR) 0.7 (95% confidence interval (CI): 0.4–1.2)), whereas 4.6% and 5.1%, respectively, had CIN3 or worse (RR 0.9 (95% CI: 0.4–2.0)). A total of 27.3% of women on DIM and 34.3% on placebo had no sign of disease (negative cytology, colposcopy and human papilloma virus (HPV) tests) at 6 months (RR 0.8 (95% CI: 0.6–1.0)). Of those HPV-positive at baseline, 69% (114 out of 166) of the DIM group were positive at 6 months compared with 61% (43 out of 71) of the placebo group: RR 1.1 (95% CI: 0.9–1.4). Diindolylmethane supplementation was well tolerated. CONCLUSION: The results suggest that short-term DIM supplementation (150 mg day(−1)) is well tolerated, but is unlikely to have an effect on cytology or HPV infection. Uncertainty remains regarding its effect on CIN2+.