Soya Intake
Soya Food Intake and Risk of Endometrial Cancer among Chinese Women in Shanghai
What is the problem and what is known about it so far?
Endometrial cancer affects the inner wall of a women's uterus. Estrogens produced in the body have a central role in the cause of endometrial cancer. Soya foods are a rich source of isoflavones, a major group of plant estrogens that have both weak estrogenic (promoting the effect of estrogen) and antiestrogenic (inhibiting the effect of estrogen) activities, depending on dose and tissue exposed.
Why did the researchers do this particular study?
Asian women have a lower incidence of endometrial cancer and eat more soya food than Western women. Therefore, the researchers wanted to evaluate the relationship between the intake of soya food and the risk of endometrial cancer.
Who was studied?
This population based case-control study looked at two groups of women. One group was made up of 832 women who had endometrial cancer in urban Shanghai, China, were between the ages of 30 and 69 years, were diagnosed between 1997-2001 and were identified from the Shanghai Cancer Registry. The second group was made up of 846 women without disease (control group) who also lived in Shanghai and were matched against the other group by age and randomly selected from the Shanghai Residential Registry.
How was the study done?
Detailed information about usual soya food intake over the past five years was collected by face-to-face interviews (by trained retired nurses) using a structured and validated quantitative food frequency questionnaire assessing usual dietary intake. From this, the intake of soya protein was used to estimate isoflavones intake. The risk of endometrial cancer was calculated for women with different intakes of soya food.
What did the researchers find?
Regular consumption of soya foods was inversely associated with the risk of endometrial cancer (the more soya foods consumed, the lower the risk of endometrial cancer). For women with the highest compared to the lowest quarter of soya protein intake, the chance of endometrial cancer was reduced by 33%; and for fresh soya beans by 37%. A similar inverse association was observed for soya isoflavones and soya fiber intake. This association seemed to be more obvious among women with high body mass index (BMI) or high waist-to-hip ratio.
What were the limitations of the study?
Although the researched tried to adjust for other dietary and non dietary factors, other explanations for the increased risk with lower soya intake may be the result of increased intake of something more harmful in place of the soya foods. Also, as with all case-control studies, potential bias (those with cancer remembering their intake of soya foods differently from those without cancer or changing their diet after diagnosis with cancer) and measurement error are the main concerns. The observation that women with a high BMI or waist-to-hip ratio may benefit more from increased soya food intake, needs further study for verification. Finally, the intake of soya foods in the study population is 25 times that of a western population so the results may not be applicable to the latter.
What are the implications of the study?
Regular intake of soya foods is associated with a reduced risk of endometrial cancer, particularly among overweight women.
Summarized by Chuan-Ju Gwendolyn Pan, College of Medicine, University of Vermont.
Summarized from "Soya Food Intake and Risk of Endometrial Cancer among Chinese Women in Shanghai: Population Based Case-Control Study". Xu, Wang Hong. et al. BMJ, May 29, 2004, Volume 328, Number 7451, page 1285.
