A plant Celts used to get blue dye for their war paint is a rich source of a compound that fights breast cancer, scientists have found.
Actors in the film Braveheart recreated the 'woad' look
Woad, which belongs to the same plant family as cauliflower and broccoli, contains high levels of the compound glucobrassicin.
The Italian team at Bologna University discovered woad contains 20 times more glucobrassicin than broccoli.
They were also able to boost its concentration by damaging the plant.
When the leaves are damaged, glucobrassicin is released by the plant as a defence mechanism.
Its derivatives can kill some plant pests. Notably, they also have anti-tumour properties and are particularly effective against breast cancer.
Researchers have already suggested that eating vegetables rich in chemicals such as glucobrassicin might help protect people against cancer.
Studies suggest that glucobrassicin flushes out cancer-causing compounds including derivatives of oestrogen.
A recent study found people who ate foods rich in glucosinolates had reduced levels of chemicals linked to smoking-related lung cancer.
But it has been difficult for scientists to extract enough glucobrassicin from plants to test its effect.
Dr Stefania Galletti and her team hope their findings will make it easier to perform such studies.
Broccoli contains glucobrassicin
"The availability of glucobrassicin in good amounts and at low cost could finally permit studies to be performed in order to clarify the anti-cancer role of glucobrassicin-rich vegetables, like broccoli, in the human diet," she told the Journal of the Science of Food and Agriculture.
Dr Kat Arney of Cancer Research UK said: "The natural world is a rich source of molecules that can benefit human health. This new way of growing woad, a plant from the same family as broccoli and cauliflower, could allow researchers to get hold of larger quantities of potential anti-cancer agents.
"These can then be tested further in the lab and in patients. Chemicals like these could one day prove to have an important part to play in the prevention and treatment of cancer."