Dietary intake of broccoli and the risk of cancer in the Prostate, Lung, Colorectal and Ovarian Cancer (PCLO) Screening Trial

Robert Thomas1,2,3, Alex McConnachie4, Bethany Stanley4, Madeleine Williams2

The Primrose Lifestyle Research Unit, Bedford Hospital, Bedford MK42 9DJ
Dept. of Oncology, Addenbrookes’ Hospital NHS Trust, Hills Rd, Cambridge CB2 2QQ
School of Sport Science and Physical Activity, Institute for Sport and Physical Activity Research University of Bedfordshire, Polhill Avenue, Bedford, MK41 9EA
Institute of Health and Wellbeing, College of Medical, Veterinary and Life Sciences, Robertson Centre for Biostatistics, University Avenue, University of Glasgow, Glasgow G12 8QQ

Presented at ASCO 2020 https://meetinglibrary.asco.org/record/189597/abstract

 

Background

The cruciferous vegetable broccoli, as well as being a good source of vitamins, minerals and fibre, are rich in the thiol phytochemicals (indole-3-carbinol), glucosinolates (isothiocyanates and its metabolite, sulforaphane), carotenoids (lutein and zeaxanthin) and flavonols (kaempferol).  Laboratory and human biopsy studies have found that broccoli intake influenced epigenetic expression of genes via blockage of histone deacetylase which reduce inflammation and cancer growth. Clinically, a randomised control study reported dried broccoli extract (along with three other foods) influenced PSA progression in men with prostate cancer1. However, no preventative intervention studies in humans have been conducted and data from cohort studies are inconsistent for its influence on cancer incidence2,3.

Method

We analysed 49,104 people within the intervention arm of the 155,000 participant PLCO screening trial. Histological confirmed cases of any cancer were reported in 8,263 (16.83%) during the 11.5 year follow up. Broccoli consumption was assessed with a food frequency questionnaire (FFQ). Baseline characteristics were compared between broccoli consumption groups using Chi-square and Kruskal-Wallis tests. Cox regression models were used to assess the association between broccoli intake and cancer incidence.

Results

Broccoli consumption was associated with reduced cancer incidence: HR 0.95 (CI 0.93-0.97, p<0.001). This pattern persisted with adjustments for age, sex, race, education level and family history (HR 0.97, CI 0.96-0.99, p=0.007) as well as smoking, BMI and alcohol consumption (HR 0.98, CI 0.96-0.99, p=0.010).

Conclusion

The study identified an association between increased broccoli consumption and reduced cancer risk. In practical terms, 15g of broccoli, or more, consumed per day (about a small cup) was associated with a 5% lower risk of cancer. Broccoli should continue to be included in healthy eating advice. This supports the inclusion of broccoli in supplements evaluated for prostate cancer.

 

References

  1. Thomas et al. The NCRN Pomi-T RCT. Prostate cancer & prostatic diseases (2014), 2,180.
  2. Liu et al Cruciferous vegetables inversely linked with breast cancer: Breast (2013), 22;3,309.
  3. Bosetti et al Cruciferous vegetables and cancer risk Ann Oncol (2012) 23(8);2198.