Scientists are testing the impact of vitamin E and a synthetic version of lycopene, a compound in tomatoes, in cancer patients after they found that the combination slowed the growth of prostate tumors in mice.

Lycopene is what gives tomatoes their rich red color. Studies have suggested that it can reduce the risk of prostate cancer.

Dr. Jacqueline Limpens, of the Erasmus Medical Center in Rotterdam, presented new research in Geneva on Thursday showing that, in mice studies, the impact of lycopene can be enhanced by using it with vitamin E.

“The combination of lycopene and vitamin E produced the most active response and the most significant,” Limpens said in a telephone news conference from the EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics.

She and her team tested low and high doses of synthetic lycopene alone and combined with vitamin E and a combination of low dose lycopene and low vitamin E against a placebo in mice injected with human prostate cancer cells.

“What was particularly marked was that it was the low dose of both lycopene and vitamin E that was the most effective, demonstrating that ‘more does not necessarily equal better,”’ said Limpens.

The combination reduced the growth of the tumors by 73 percent by the 42nd day of the trial.

A study testing the compounds in cancer patients is now under way. Prostate cancer kills about 200,000 men each year, mostly in developed countries. Most men diagnosed with the disease are usually 65 or older.

The incidence of the disease is rising in many countries but experts believe it is due largely to improved screening. It is usually treated with surgery or radiation treatment.

Limpens said the findings are in line with research suggesting that vitamin E and lycopene could have a protective effect against prostate cancer.

“Therefore we would certainly recommend that all men regularly eat lycopene and vitamin-E-rich foods; for example, all kinds of processed tomato products, papayas, pink grapefruit and watermelon, wheat germs, whole grains, mangoes, leafy green vegetables, nuts and olive oils,” she added in a statement.