Tomatoes are the most concentrated food source of lycopene.
Women who eat more tomatoes or other lycopene-containing fruits and vegetables may have a lower risk of developing kidney cancer, a new study suggests.
Lycopene is an antioxidant that gives tomatoes, watermelon, grapefruit and papaya their reddish color, and some studies have suggested it may reduce the risk of a number of cancers, including lung and stomach cancer.
In the new study, the researchers looked at nearly 92,000 postmenopausal women, following them from the mid-1990s to 2013. All of the women were participants in the Women's Health Initiative, a long-term nationwide study designed to help researchers better understand the causes of disease in middle-age and older women.
The amount of micronutrients including lycopene in the women's diets was estimated from the information they provided on questionnaires when they enrolled in the study. The researchers also gathered data on the women's supplement use. [5 Key Nutrients Women Need As They Age]
During the study period, 383 women were diagnosed with kidney cancer. The researchers looked at the relationship between kidney cancer and a number of vitamins and other nutrients in the diet, including lycopene, vitamin C, vitamin E and several carotenes.
The results showed that only lycopene was associated with a lower kidney cancer risk. Women who consumed the highest amount of lycopene had a 45 percent lower risk of kidney cancer compared with those who ate the lowest amount, according to the study, presented Monday (June 2) at the annual meeting of the American Society for Clinical Oncology in Chicago.
The amount of lycopene in the diet of the women who consumed lycopene at the highest level in the study would be equal to eating four tomatoes daily, said study researcher Dr. Won Jin Ho, a medical resident at Case Western Reserve University in Ohio.
However, it's likely that the women received lycopene not just from tomatoes, but also from tomato sauces and other fruits that contain lycopene, Ho said.
Kidney cancer, also called renal cancer, is the ninth most common cancer among Americans, and accounts for about 2 percent of all cancers in the United States, according to the Centers for Disease Control and Prevention.
Kidney cancer often doesn't cause symptoms in its early stages, and is often diagnosed accidentally during a medical examination, or not until the cancer has progressed. In later stages, signs of the cancer include blood in the urine, back pain and general feeling of poor health. But these symptoms could also be signs of other health problems, such as infections.
Studies have suggested that a process known as oxidative stress may play an important role in the development of kidney cancer, the researchers said. A diet rich in micronutrients that have antioxidant properties could potentially affect the risk of this cancer, but more studies are needed to know for sure, they said.