Red chilli pepper has previously been linked to inhibiting the growth of pancreatic cancer cells, and has been suggested to cut fat and energy intake when added to the diet.
"We show that capsaicin has a profound inhibiting effect on the growth of prostate cancer cells in vitro and in vivo , inducing apoptosis [programmed cell death] of prostate cancer cell lines," wrote lead author Akio Mori from the University of California, Los Angeles.
The new study, published in the journal of Cancer Research (Vol. 66, pp. 3222-3229), showed that the protein NF-kappaB, shown to be active in hormone-independent prostate cancer cells in vitro, was significantly inhibited by the capsaicin.
The chili pepper compound also had an effect on the androgen response (AR)-regulated prostate-specific antigen (PSA) gene, a well-known marker of prostate cancer cells.
These effects induced the apoptosis of the cancer cell lines.
To test the in vivo effectiveness of capsaicin, the researchers injected prostate cancer cell lines into mice models and gave the mice capsaicin by gavage (direct into the stomach by a tube).
The doses given were equivalent to 400 milligrams of capsaicin, three times a week, for a man of 91 kg (200 pounds).
After four weeks, tumour size decreased significantly in the capsaicin group compared to the control group: 75 compared to 336 cubic millimetres.
"Capsaicin inhibits the growth of prostate cancer tumours growing in mice without causing gross toxicity of the animals," said Mori.
Chris Hiley, head of policy and research at The Prostate Cancer Charity said the research was interesting, but questioned whether a lab experiment would work the same in men.
"We caution men with prostate cancer in the UK against upping their weekly intake of the hottest known chillies. High intake of hot chillies has been linked with stomach cancers in the populations of India and Mexico," said Hiley.
This was echoed by Kat Arney, science information officer at Cancer Research UK: "Although chilli peppers may be tasty, this research does not suggest that eating vast quantities can prevent or treat prostate cancer. In fact, eating too many hot chillies can lead to stomach cancer. A low-fat diet rich in fruit and veg - including the occasional chilli - can help to reduce the risk of cancer."
Over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years, according to the European School of Oncology.