Study finds birth control
cuts ovarian cancer risk
A nutrient in carrots also showed
benefits in the Hawaii study
Women who use oral contraceptives reduce their risk of ovarian cancer by 40 percent or more, according to a study by the Cancer Research Center of Hawaii.
High consumption of carrots or other products with vitamin A or beta carotene also may be "modestly protective" against the fatal cancer, the researchers recently reported.
The ovarian cancer study, entering its 10th year, is supported by a National Cancer Institute grant to Dr. Marc Goodman at the Cancer Research Center of Hawaii.
Dr. Ko-Hui Tung, formerly a post-doctoral researcher in epidemiology at the research center, was first author of the beta carotene study published last month in the journal Cancer Epidemiology Biomarkers and Prevention.
The primary message is to eat carrots or drink carrot juice, said Tung, who recently joined Kaiser Permanente Hawaii's Center for Health Research.
"Our results show the total dietary effect of beta carotene, not only from diet but supplements," she said, pointing out beta carotene can convert to vitamin A.
"It's particularly important for smokers," she said. "They might benefit the most."
The study is the first to report benefits to smokers from high consumption of vitamin A and effects of beta carotene on ovarian cancer risk, Tung said.
In an earlier study, high vitamin A and beta carotene consumption were associated with reduced risk of breast cancer among smokers.
Researchers from the Norris Comprehensive Cancer Center of the University of Southern California participated in the study with the Cancer Research Center of Hawaii.
The same group, in a study published in the American Journal of Epidemiology in 2002, found high calcium intake significantly reduced ovarian cancer risk.
The beta carotene study followed 1,200 Hawaii and Los Angeles residents from 1993 to 1999. The multiethnic participants had no history of ovarian cancer.
"It's prudent to eat a healthy diet no matter what," Goodman said. "With ovarian cancer, diet is probably important, but not nearly as important as hormones."
He said oral contraceptives have gotten "a very bad rap" because original formulations contained high levels of estrogen.
But "we've learned over the years a very modest amount of estrogen, counteracted by progesterone, does protect against a variety of cancers, ovarian and endometrial, and maybe modifies risk of certain heart disease," he said.
"It's also good for women with problems regulating their menstrual cycle," he added. "I'm not one who feels oral contraceptives should be discarded.
"In terms of public health significance, right now oral contraceptives are the only chemical agent that can prevent ovarian cancer."
Goodman cited data showing women who used oral contraceptives for two years had a 36 percent reduction in risk; those using them two to five years had a 49 percent risk reduction, and women using them for five years or more had a 64 percent reduction.
"So the longer you use it, the better," he added.
Ovarian cancer is probably one of the most complex and difficult cancers to study, Goodman said. "It comes in a variety of different forms. They're all quite serious, but certain types are highly fatal."
Goodman recently attended a meeting at Oxford University of about 38 research groups that are pooling data.
More cancer cases and controls are needed to explain two matters of great interest: how oral contraceptives and hormone replacement therapy affect risk, Goodman said.
Research has focused on diet, but a new study will look at genetic variations that might explain some differences in risk between population groups, he said.
Researchers will focus on genes that regulate hormones, which are strongly implicated in ovarian cancer risk, he said.
Other Hawaii Cancer Center researchers who worked on the beta carotene study were Dr. Laurence N. Kolonel, Abraham M.Y. Nomura, Dr. Jean H. Hankin, Katharine McDuffie and Lynne Wilkens.