In a recent review and meta-analysis published in the journal Nutrients, researchers compiled, statistically evaluated, and discussed the returns from previous literature on the effects of broccoli consumption on various types of cancer. They searched five online scientific repositories and identified 23 case-control and 12 cohort studies relevant to the topic under investigation. Their findings from a combined sample group of more than 730,000 individuals showed that low broccoli consumption was associated with a higher prevalence of cancers, suggesting that frequent consumption of this cruciferous vegetable may provide a protective effect against many cancers.
Unfortunately, the included case-control studies showed only marginal statistical significance in most trials, and the combined studies were considered insufficient to establish the chemopreventive properties of broccoli, the researchers stress that caution should be used when interpreting the results of the present work. Despite these limitations, broccoli is widely regarded as a healthy food item, with few adverse effects reported from its consumption, even exceeding the recommended daily intake. Although more research is needed before the biological mechanisms of broccoli’s cancer-specific benefits can be confirmed, the overall benefits of broccoli consumption are clear.
‘Cancer‘ is an umbrella term that refers to a spectrum of diseases characterized by the uncontrolled and abnormal growth and division of the body’s cells. It is a dangerous and often life-threatening condition that is currently second only to cardiovascular diseases (CVDs) in claiming human lives annually. Despite significant medical advances that have reduced cancer-related mortality since the late 1990s, in developed countries, mortality from this disease exceeds that of CVDs, with more than 10 million patient deaths and 19.3 new cases of cancer in 2020 alone. Millions more.
In particular, following the coronavirus disease 2019 (COVID-19) pandemic, modifiable health behaviors, particularly sleep, physical activity, and dietary habits, have gained popularity among scientists and the health-conscious public. Research shows that just a few changes in these behaviors can have profound benefits against chronic diseases including CVD, cancers, and mental health conditions. Cruciferous vegetables are of particular epidemiological interest due to their inherent abundance of known anticancer biomolecules such as isothiocyanate precursors, glucosinolates, and indole-3-carbinol.
Unfortunately, although several studies suggest that cauliflower, cabbage, Brussels sprouts, and broccoli are beneficial in several types of cancer (lung, gastric, pancreatic, colon, kidney, ovarian, prostate, and breast), these studies generally include small sample cohorts, have insufficient follow-up periods, and often leads to confusing results. So far, no meta-analysis has attempted to elucidate the benefits of broccoli (Brassica oleracea var. italica) in reducing cancer risk. In addition to sharing the benefits of the cruciferous vegetables listed above, broccoli is a rich source of sulforaphane and myrosinase, both powerful antioxidant modulators and known anti-cancer compounds, suggesting that its consumption may inhibit the growth and progression of cancer.
The current meta-analysis examines the association between varying amounts of broccoli (high versus low or none) and subsequent cancer risk. It also seeks to elucidate the biological mechanisms underlying the observed benefits. The study states Preferred Reporting Items for the Guidelines for Systematic Reviews and Meta-Analyses (PRISMA 2020). Publications for meta-analysis (including current abstracts and unpublished studies) were retrieved from five electronic databases.
Of the 3,026 articles initially identified and collected from the database search, title and abstract screening identified 183 potential publications of interest. Full-text screening further narrowed this dataset to a final group of 49 publications (for review) and 35 (for meta-analysis). Of these, 16 were cohort studies (total sample size = 1,512,760 participants), and 33 case-control studies (total n = 43,448).
Results of a random effects model found an inverse relationship between broccoli intake and subsequent cancer incidence, highlighting a protective effect against the latter. Encouragingly, these effects were consistent across both cohort and case-control studies. However, unfortunately, although consistent, the results are not robust, with a severe lack of adequate cohort studies and case-control studies depicting only borderline statistical significance and a moderate degree of heterogeneity revealed across publications. Studies elucidating the biological mechanisms by which broccoli confers protection were also limited.
In summary, while current evidence suggests that broccoli consumption may reduce cancer risk, substantial future research is needed into the biological mechanisms underlying this correlation and confirmation of the association before broccoli can be included as a clinical intervention in high-risk populations.
