The researchers, from the University of East Anglea (UEA) in the UK, publish their results in the American Journal of Clinical Nutrition.

According to the team, ovarian cancer affects over 6,500 women in the UK and 20,000 women in the US each year. Epithelial ovarian cancer - the most common form of the disease - is where the cancer begins in the surface layer covering the ovary.

This type of cancer "remains a highly lethal malignancy," note the researchers, adding that few modifiable risk factors have been established.

However, some previous studies have suggested that a diet rich in fruits and vegetables may be associated with a decreased risk, but subsequent studies have produced inconsistent findings.

Plants contain flavonoids that adjust key cellular signaling pathways and regulate cancer-inflammation pathways, note the team, which suggests flavonoids might be the compounds in plants that could reduce ovarian cancer risk.

Flavonoids include flavonols - found in tea, red wine, apples and grapes - and flavanones - found in citrus fruit and juices.

'Just a couple cups of black tea daily linked with a 31% reduction in risk'

To further investigate the link between flavonoid intake and ovarian cancer risk, the researchers studied dietary habits of 171,940 women aged between 25-55 as part of the Nurses' Health Study and Nurses' Health Study II over the course of 3 decades.

"This is the first large-scale study looking into whether habitual intake of different flavonoids can reduce the risk of epithelial ovarian cancer," says lead author Prof. Aedin Cassidy, from UEA's Norwich Medical School.

To calculate the participants' dietary intake, the researchers analyzed validated food-frequency questionnaires that were collected every 4 years and found that main dietary sources of flavonols were black tea (31%), onions (20%) and apples, while the main sources for flavanones were citrus fruit (36%; 27% from orange intake) and juices (63%; 54% from orange juice).

During the 16-22 years of follow-up, the researchers found that there were a total of 723 cases of medically confirmed ovarian cancer.

Results show that participants who had the highest intakes of flavonol and flavanone had a lower risk of developing epithelial ovarian cancer than those who had the lowest intakes.

The research team, from the University of Montreal's School of Public Health in Canada, publish their findings in the journal Cancer Epidemiology.

According to the researchers, the link between sexual activity and prostate cancer risk remains controversial. Some studies have associated high sexual activity with a greater risk of the disease, while others have suggested the opposite.

In this study, the team set out to determine whether the number of sexual partners men have throughout their lifetime influences their risk of prostate cancer.

They analyzed 3,208 men who were part of the Prostate Cancer & Environment Study (PROtEuS) in Montreal, Canada. Of these, 1,590 were diagnosed with prostate cancer between 2005 and 2009, while the remaining 1,618 men were free of the disease.

As part of this study, all men were required to complete a questionnaire that asked about their sexual activity, as well as sociodemographic, environmental and lifestyle factors.

28% lower prostate cancer risk among men who slept with more than 20 women

The team was not surprised to find that men who had a relative with prostate cancer were twice as likely to have the disease themselves. A family history of prostate cancer is a well-established risk factor.

However, the researchers found that a man's prostate cancer risk also appeared to be influenced by the number of sexual partners he had in his lifetime.

Men who reported never having a sexual partner were twice as likely to develop prostate cancer than those who reported having sexual partners.

However, the team found that men who had slept with more than 20 women in their lives had a 28% lower risk of developing all types of prostate cancer and a 19% lower risk of developing aggressive prostate cancer, compared with those who had slept with fewer than 20 women.