The new study found that higher consumption of foods rich in flavonoids - including black tea and citrus fruits - is linked to a reduced risk of epithelial ovarian cancer.
The researchers, from the University of East Anglia (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.
Commenting on their findings, Prof. Cassidy says:
"The main source of these compounds include tea and citrus fruits and juices, which are readily incorporated into the diet, suggesting that simple changes in food intake could have an impact on reducing ovarian cancer risk.
In particular, just a couple of cups of black tea every day was associated with a 31% reduction in risk."
Study has limitations
Some strengths of the study include its large sample size with long-term follow-up, repeated assessments of dietary intake and detailed data on ovarian cancer risk factors. However, the researchers identify some limitations.
Fast facts about ovarian cancer in the US
- In 2014, an estimated 21,980 new cases and 14,270 deaths due to ovarian cancer will occur
- Around 1.3% of women will be diagnosed with ovarian cancer at some point in their lives
- In 2011, there were an estimated 188,867 women living with ovarian cancer in the US.
For example, the mean cumulative dietary flavonoid intakes were calculated from recent US Department of Agriculture (USDA) databases with input from other sources, but flavonoid contents can vary in foods, depending on growth and processing conditions.
Additionally, while the team adjusted for possible confounders linked with ovarian cancer risk, they say there was still the possibility of "residual confounding from unmeasured factors."
Still, they add that "because of our detailed and updated adjustment for potential confounders, it was unlikely that these would have accounted fully for the observed results."
Theirs is the first study to assess the six major flavonoid subclasses in a normal diet and look at it in terms of ovarian cancer risk, and it was also the first study to look into the impact of polymers and anthocyanins, they note.
The team concludes that "higher intakes of flavonols and flavanones as well as black tea consumption may be associated with lower risk of ovarian cancer," but they add that additional prospective studies are needed to confirm their results.
Medical News Today recently reported on a potential personalized vaccine to treat ovarian cancer, stemming from a new technique that identifies protein mutations in cancer cells.