The researchers, from Milan in Italy, have now called for a prospective study to investigate further the possible links between diet and endometriosis.
Endometriosis is a painful and distressing condition whereby endometrial tissue, which under normal circumstances is found only in the lining of the womb, develops outside the uterus and attaches itself to ligaments and organs in the abdominal cavity. This tissue responds to the menstrual cycle as though it were still inside the uterus. The repeated growth and disintegration of endometrial tissue in the abdomen can cause bleeding, pain, inflammation, adhesions and infertility. It is estimated to affect up to five in every 100 women in Italy and probably in the rest of Europe.
The researchers used interviews and structured questionnaires to compare the medical and reproductive history, lifestyle and diet of over 500 women with clinically confirmed endometriosis with a group of over 500 matched controls with no history of the disease.
Lead researcher Dr Fabio Parazzini from the Gynaecologic Clinic of the University of Milan, explained: "We asked women about their diet in the year leading up to the interview. In particular, we asked how many times a week they ate portions of selected dietary items, including the major sources of retinoids and carotenoids in the Italian diet. We also asked about their alcohol and coffee consumption.
"We divided their intake into portions approximating to low, intermediate and high intake of the various dietary factors. What we found was that there was a 40% relative reduction in risk of endometriosis in women with higher consumption of gr