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.)
What Current Evidence Shows: AICR/WCRF Expert Report and its Updates (CUP)
Cruciferous vegetables are non-starchy vegetables that contain dietary fiber and carotenoids (including beta-carotene). After a systematic review of the global scientific literature, AICR/WCRF weighed the strength of the evidence linking these factors to lower risk for several cancers.
|Diets high in:||CONVINCINGLY lower risk of the following cancers:|
|Foods containing dietary fiber||Colorectum|
|Diets high in:||PROBABLY lower risk of the following cancers:|
|Non-starchy vegetables||Mouth, pharynx and larynx|
|Foods containing carotenoids||Mouth, pharynx and larynx
Source: Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective and the 2011 Continuous Update Project: Colorectal Cancer.
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.