If you're a smoker, eating your vegetables may reduce your risk of developing lung cancer, a new study suggests.

American researchers have found that eating cruciferous vegetables led to between a 20 per cent and 55 per cent reduction in lung cancer risk, depending on the type of vegetable and how long the subject had been a smoker.

Cruciferous vegetables are part of the cabbage family and include broccoli, cauliflower and Brussels sprouts.

The research also showed that only the consumption of raw, as opposed to cooked, cruciferous vegetables reduced lung cancer risk in current smokers.

"Broccoli is not a therapeutic drug, but for smokers who believe they cannot quit nor do anything about their risk, this is something positive," Li Tang, a post-doctoral fellow at Roswell Park Cancer Institute, said in a statement. "People who quit smoking will definitely benefit more from intake of cruciferous vegetables."

The findings were presented at the American Association for Cancer Research's International Conference on Frontiers in Cancer Prevention Strategy.

Cruciferous vegetables are high in vitamins and minerals and have been proven to have a protective effect against cancer.

In July, British researchers found that men who eat one or more servings of broccoli per week can reduce their risk of developing prostate cancer. That study also found that men who follow a broccoli-rich diet can help prevent a prostate cancer tumour from becoming more aggressive.

The new findings showed that cruciferous vegetables were especially effective at reducing the risk among the subtypes of lung cancer that are most strongly associated with heavy smoking: squamous and small-cell carcinoma.

The new findings are "not strong enough to make a public health recommendation yet," Li said.

However, the study adds to the evidence that cruciferous vegetables may play a key role in cancer prevention, particularly among smokers.