Researchers led by Dr. Jacqueline Limpens from the Erasmus Medical Center in Rotterdam, said yesterday that the combination slowed the growth of prostate tumours in mice and that a study testing the compounds in cancer patients is now under way.
She and her team tested low and high doses of synthetic lycopene, the carotenoid found naturally in tomatoes, alone and combined with vitamin E against a placebo in mice injected with human prostate cancer cells.
"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.
She reported that the combination reduced the growth of the tumors by 73 per cent by the forty-second day of the trial.
"We would certainly recommend that all men regularly eat lycopene and vitamin-E-rich foods including processed tomato products, papayas, pink grapefruit and watermelon, wheat germs, whole grains, mangoes, leafy green vegetables, nuts and olive oils," she added.
Earlier this year, researchers from DSM were the first to discover - in experiments carried out on a rat model - that lycopene may reduce the risk of prostate cancer by inhibiting the male hormone's effect on the prostate, and that feeding the rat vitamin E and lycopene in combo caused an enhanced killing rate of tumour cells.
Their analysis revealed that both nutrients affected gene expression directly in the tumours: lycopene interfered with local androgen activation by down-regulating 5-alpha-reductase, the key enzyme for the transformation of testosterone to its most active form dehydrotestosterone (DHT). As a consequence, the expression of androgen-regulated target genes was also reduced.
In addition, lycopene decreased the expression of two prostatic cytokines, IGF-I and IL-6, both regarded as risk factors for prostate cancer. Vitamin E reduced androgen signaling without affecting androgen metabolism.
Prostate cancer is one of the biggest cancer killers in industrial countries and affects more than 500,000 men worldwide every year. This number is expected to increase with the ageing population.