High soy intake in early-life linked to breast density and may reduce cancer risk, study finds
Mammographic density - the proportion of dense breast tissue seen on a mammogram - is a well-established predictor of breast cancer risk.
Soy foods, which include tofu, soy milk and other soy-based products are frequently used in traditional Asian diets.
The study, led by Professor Suzanne Ho Sut-ying at The Chinese University of Hong Kong (CUHK) and funded by World Cancer Research Fund, assessed the lifetime soy intake of 815 healthy premenopausal women aged 35-45 in Hong Kong across different life stages, including childhood, adolescence, young adulthood and recent intake.
It found that women with consistently high soy intake during early-life had approximately 6% lower breast density than those with consistently low early-life intake.
The results suggest that early-life soy exposure may influence adult breast tissue composition and could provide long-term protective effects on breast tissue in the development of breast cancer. It follows growing evidence suggesting that the stage of life that soy is consumed may be as important as how much is consumed.
In particular, it is thought that soy consumption during early-life may have a strong influence on later breast cancer risk by affecting mammary gland development. However, evidence linking soy intake at specific life stages to adult breast density has remained limited.
As well as taking mammograms, the research team assessed soy consumption using a validated soy food frequency questionnaire covering 32 soy products. Participants reported their current intake, as well as retrospective intake during childhood, adolescence and young adulthood, with recall supported by life-history cues.
After adjusting for confounding factors including age, waist circumference, and physical activity, the researchers found that soy protein intake during adolescence and childhood was significantly and inversely associated with adult breast density. In contrast, recent soy intake was not associated with breast density.
The authors emphasise that the study is observational and based on self-reported information. Further studies would help to validate if soy intake directly contributes to the lowering effects on breast density or reduces breast cancer risk.
Soy foods contain isoflavones, bioactive compounds that can interact with oestrogen-related pathways. The findings add to growing evidence that the timing of dietary exposure may be important, with childhood and adolescence representing a key developmental window where the mammary gland undergoes rapid structural and hormonal changes which could influence cancer susceptibility.
Professor Suzanne Ho
Professor Suzanne Ho, Emeritus Professor of CUHK, said: “Our findings suggest that soy consumption earlier in life, particularly during childhood and adolescence, is associated with lower breast density in adulthood. As we did not see the same association for recent soy intake, it points to early-life exposure as a potentially important window for breast tissue development in later life."
“Soy is a common component of traditional Asian diets, and this study adds to evidence suggesting that the timing of exposure to soy foods may matter. More research is needed to confirm these findings and to understand whether modifying early-life soy intake could contribute to breast cancer prevention.”
Dr Giota Mitrou
Dr Giota Mitrou, Executive Director of Research and Policy at the World Cancer Research Fund International, said: “While characteristics such as overweight and obesity are well established factors linked to breast cancer risk, only a limited number of studies have evaluated the association between soy intake and breast density, and so far, findings remain inconclusive."
“This study adds to our understanding of how exposures across the life course may shape cancer risk, which is a key area of work for World Cancer Research Fund. It raises the possibility that breast tissue may be particularly susceptible to dietary influences during specific developmental windows and highlights the need for further research into dietary patterns in different population groups.”
Professor Anne Lee
Professor Anne Lee, Hong Kong Ambassador at the World Cancer Research Fund International, said: “By looking at soy intake during childhood, adolescence, young adulthood and later life among Chinese premenopausal women, the research points to the possible importance of nutrition early in life in influencing breast density in adulthood."
“This study provides useful observational evidence for the idea of ‘early-life nutritional programming’ and highlights the possibility that diet early in life could play a role in reducing breast cancer risk. Furthermore, the use of a Life History Calendar (LHC) with audiovisual aids to enhance the recall of distant dietary habits is a notable methodological innovation.”
