Do broccoli and cabbage help fight tumour growth?
Broccoli and cabbage contain compounds that clearly slow tumour growth in animal and laboratory studies, and people who eat a lot of them are found to develop cancer less often. Whether that is cause and effect, and what amount is helpful, has not yet been established: eating more broccoli is a sensible choice, but it is not a replacement for standard treatment.
People who eat a lot of broccoli are less likely to develop cancer, according to studies. That association is strong enough to take seriously, but it has not been proven that broccoli itself is the cause. Other healthy habits may also play a role.
The active compound behind this effect is sulforaphane, a substance released when you chew broccoli or cabbage. In animal studies, sulforaphane reduced the amount of prostate cancer tissue by around 61 per cent, accompanied by greater cell death and lower production of the fats that tumour cells need. In cell and animal studies, similar compounds from cabbage and broccoli also slow breast cancer cell growth, the formation of new blood vessels, and the spread of cancer. What this means for people is not yet clear: results in people have been mixed.
A small study in people with prostate cancer was also carried out, using a broccoli supplement. Among the 19 people who took the supplement for four weeks, production of the proteins that drive tumour growth in prostate tissue fell. The study is small, and the researchers themselves note that a longer period of use is likely needed.
In studies, sulforaphane does more than simply slow tumour cells: it activates a protective system in the body that makes cells more resilient against harmful substances, and it protects the liver, lungs, heart and kidneys in laboratory and animal studies. What amount is safe for people has not yet been established. For prostate cancer specifically, laboratory studies and broader reviews of the evidence show that sulforaphane blocks several growth signals, but direct evidence from studies in people is still limited.
This answer draws on a combination of research in which people were followed for years (for the general cancer risk associated with broccoli consumption), animal and cell studies (for sulforaphane and isothiocyanates), and one small study in 41 people with prostate cancer. The animal and laboratory results are consistently positive, but in people the results are mixed or still limited in scale. For the prostate cancer study, the group was very small and the treatment period short. The researchers behind the broader isothiocyanate research emphasise that the right dose, form of delivery and combination with other treatments have not yet been established.