The findings add to a number of benefits attributed to the B vitamin, recommended especially for women of child-bearing age in order to reduce the risk of birth defects in newborns.
Writing in the Journal of the National Cancer Institute(vol.96, no.5, 396-402), the researchers from Stockholm's Karolinska Institute showed that women who consumed the highest amount of folate reduced their risk of ovarian cancer by 33 per cent compared to women who consumed the least amount of the vitamin.
But the benefits may be greater in women who consume more than two alcoholic beverages per week. These reduced their risk by 74 per cent compared to women consuming lesser amounts of alcohol if they also had high levels of folate.
Ovarian cancer affects more than 1,000 women a year in the UK, and is dangerous because it can often be at an advanced stage before symptoms appear and it is detected.
The research was based on data from the Swedish Mammography Cohort, a population-based prospective cohort of 61 084 women, aged 38-76 years, who were cancer-free at baseline.
There is previous evidence to show that folate may also protect against breast and colorectal cancers, especially among alcohol drinkers. Alcohol interferes with folate metabolism and has opposing effects on the risks of cardiovascular disease and cancer.
A Harvard team demonstrated last year that the increased risk of major chronic disease associated with heavy drinking was largely diminished among women with a higher folate intake.
Folic acid is also thought to protect both men and women from stroke and mental diseases.