The Cancer Research
The link between cruciferous vegetables and their components to cancer prevention is relatively well-studied.
AICR/WCRF’s expert report and its updates group cruciferous vegetables – and most green vegetables – as non-starchy. (Corn and potatoes, on the other hand, are examples of starchy vegetables.)
Current Evidence: AICR/WCRF Expert Report and its Updates (CUP)
After a systematic review of the global scientific literature, AICR/WCRF analyzed how cruciferous vegetables and its nutrients affect the risk of developing cancer. This comprehensive review of decades of research concluded that there is strong – probable - evidence that:
- foods containing dietary fiber DECREASE the risk of colorectal cancer
- a diet high in non-starchy vegetables along with fruits DECREASE the risk of lips, mouth, tongue and other aerodigestive cancers
Evidence categorized as "probable" means there is strong research showing a causal relationship to cancer – either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings. A probable judgement is strong enough to justify recommendations.
Source: AICR/WCRF. Diet, Nutrition, Physical Activity and Cancer: A Global Perspective, 2018.
Genetic differences mean that some people retain cruciferous vegetables’ isothiocyanate compounds in the body longer -- and benefit more -- than others.
Open Areas of Investigation: Laboratory Research
Cruciferous vegetables are a large group, and each kind contains numerous vitamins, minerals and phytochemicals studied in the lab for cancer protection. Some of the more well-studied compounds include:
- Glucosinolates, which are broken down into isothiocyanates and indoles. Lab studies have shown these compounds decrease inflammation, a risk factor for cancer. The compounds also inhibit enzymes that activate carcinogens and stimulate enzymes that de-activate carcinogens. Studies suggest the compounds "turn on" genes that suppress tumors, slowing cancer cell growth and stimulating a process called apoptosis in which cancer cells self-destruct. Some studies show that these substances may also shift the active form of estrogen into a weaker form. (High amounts of estrogen are a risk factor for certain hormone-linked cancers.)
- Carotenoids act as antioxidants. Beta-carotene, one of the more well-known carotenoids, also promotes cell communication that helps control abnormal cell growth.
- Vitamin C protects cells as an antioxidant and by supporting the immune system.
- Kaempferol, quercetin and anthocyanins provide antioxidant and anti-inflammatory effects. In cell and animal studies, they slow development of several stages and types of cancer.
- Folate helps maintain healthy DNA and keeps cancer-promoting genes “turned off.” Animal studies, however, suggest that exceptionally high amounts or intervention after cancer cells have formed might promote development of colon and perhaps other cancers.
Open Areas of Investigation: Human Studies
Earlier population studies found a strong link between greater consumption of cruciferous vegetables and lower risk of lung, colorectal, stomach, breast, prostate and other cancers. Among more recent, well-designed studies, the specific link between cruciferous vegetables and reduced cancer risk is not as consistent or strong. One reason may have to do with specific gene-diet interactions that are only now coming to light. For example, scientists recently found that about half of the population does not carry a specific gene involved in determining how long the body retains -- and utilizes -- protective cruciferous compounds from the diet.
More research is underway, including intervention trials investigating the possibility that isothiocyanates might interfere with prostate cancer progression.
Quite a few studies link consuming too little dietary folate with increased risk of colorectal cancer or pre-cancerous polyps. Recent studies also show a link between relatively high amounts of folic acid -- the form of folate found in supplements and fortified foods -- and increased risk of colorectal cancer. There is no evidence that consuming high amounts of foods naturally high in folate increases cancer risk.