Some of the better documented foods are garlic, tomatoes and over recent years more substantially broccoli and broccoli sprouts. Tomatoes are colored red by a phytochemical lycopene. Lycopene has been studied in animal models and seems to be related to a substantial reduction in risk of prostate cancer and at a cellular level it’s thought to inhibit the proliferation of breast, lung and endometrial carcinoma cells.
Interest in garlic is associated with various substances such as quercetin, allixin, allcin, allinin and allyl sulfides, which are suggested to have an inhibitory effect on prostate, colon, bladder and stomach cancer. Diallyl disulfide is a separate compound, which has been linked to a massive reduction in skin cancer, and this is also suggested to have an inhibitory impact on leukemia cells.
Unfortunately, all these studies look at the suggestive impact of vegetable-based compounds on the progress of cancer and not the actual curative effects, which are still yet to be confirmed. However, there may be some positive news for prevention of, and recurrence of cancer with our little green friend, broccoli.
Broccoli has long since been proclaimed for its super food status as an antioxidant, but it has also been studied to a great extent for its impact on proliferation of cancer cells. Broccoli has various naturally occurring chemicals within it. The one of most pharmacological interest is glucoraphanin, a precursor of sulforaphane, which is produced when myrosinase—an enzyme in the glycoside hydrolase family—transforms glucoraphanin into sulforaphane. These enzymes are released when the cells of the vegetable are damaged, which occurs during the chewing mechanism and are well documented to be involved in defense mechanisms of cells. The activity of sulforaphane is associated with the activation of transcription factor Nrf2, which among other things is also involved in regulation of tumor growth especially in established cancers.
Although broccoli has been touted as an important part of a healthy diet for nearly 50 years it wasn’t until the 1990s when sprouts were determined to have potential additional benefits. In 1997 it was discovered that 3-4 day old broccoli sprouts were the holders of up to 20 times the concentration of glucoraphanin when compared to the adult plant. Although these sprouts aren’t necessarily as rich in other nutritional compounds as fully-grown broccoli, and are ranked as having a lower dietary value according to the USDA, the available concentrations of glucoraphanin make them interesting to researchers investigating their therapeutic effect in cancers.
The extraction of concentrated extracts of broccoli is making it into the press more and more frequently. In 2013 Sally Dickinson, working at the University of Arizona, suggested that topical preparations of broccoli extract could potentially prevent skin cancer in patients with compromised immune systems working on the mechanisms of sulforaphane activity.
In early 2015 research results were released by an investigating group based at the University of Pittsburgh Cancer Institute having considered the impact of broccoli sprout extract on oral cancer in mice, and on prevention of oral cancer in healthy patients. Secondary oral cancers are common in patients who have had curative treatment for head and neck cancer, and can often prove fatal, making the prevention or reduction of risk of this occurring incredibly important in this group of patients.
The research group led by Julie Bauman, working in collaboration with Daniel Johnson initially treated mice predisposed to head and neck tumors with sulforaphane in order to determine the effect on tumor formation. Results showed that mice fed the broccoli extract developed fewer tumors than mice of the same genetic make-up who didn’t, indicating an inhibitory effect. This was followed by a small pre-clinical trial of 10 healthy human subjects who either drank the broccoli extract for several days. Cellular examination of the oral mucosa revealed that the same pathway had been activated as in the previously treated mice indicating the defense mechanism had been stimulated in the human guinea pigs.
These results have now been published in Cancer Prevention Research in June 2016 alongside the announcement of a larger study of 40 human subjects who have previously been successfully treated and cured of head and neck cancer, which is currently underway. This trial involves subjects taking a preparation of encapsulated broccoli powder for convenience and indicates a tablet form could be near. While this trial is ongoing there will be intense interest in the outcome of the research especially for the patients at risk of oral cancer.
In December 2015 researchers based at the Texas A&M Health Sciences Center released data suggesting that not only could dietary supplements for broccoli sprouts be used to prevent colon cancer, but also potentially to enhance effectiveness of standardized treatments. A separate study published in the journal Clinical Epigenetics illustrated that a healthy study group of 28 human subjects over the age of 50, who were investigated for their cruciferous vegetable eating habits demonstrated an increased expression of the tumor suppressor gene p16 upon examination of colon biopsy samples if they ate larger quantities of these vegetables. It is thought that those who eat more sulforaphane containing food stuffs are able to better prevent tumor growth.
So there is increasing positive evidence for eating your broccoli and broccoli sprouts. To be fair it includes cauliflower as well. So what do we do now? As things stand there is no absolute evidence that sulforaphane has a curative effect on cancer, and certainly it isn’t in a position to displace traditional chemotherapy or radiotherapy, but I’m sure anyone involved in the research would suggest making sure you eat your greens!
Adele is a design consultant who works in product development for medical and healthcare applications. Her background is in pharma, and she has a degree in applied physiology.