A high intake of soy products in early life is associated with lower mammographic density in adulthood, a well-established predictor of breast cancer risk.

The study, led by the Chinese University of Hong Kong and funded by the World Cancer Research Fund, assessed the lifetime soy intake of 815 healthy premenopausal women aged 35-45 across four life stages: current intake, young adulthood (20-34 years), adolescence (13-18 years) and childhood (6-12 years).

All study residents were based in Hong Kong. Soy foods such as tofu, soy milk and other soy-based products are a common component of traditional Asian diets.

Researchers found women consuming a high intake of soy products during early life had a 6% lower breast density than those with consistently reduced intake in childhood and adolescence.

The proportion of dense breast tissue seen on a mammogram (mammographic density) is a well-established predictor of breast cancer risk. As well as taking mammograms, the researchers assessed soy consumption using a validated soy food frequency questionnaire covering 32 soy products. 

Potentially important window

“Our findings suggest that lower soy consumption earlier in life, particularly during childhood and adolescence, is associated with lower breast density in adulthood,” said Suzanne Ho, emeritus professor of epidemiology and public health at the Chinese University of Hong Kong, who led the study. “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.”

She added: “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 understand whether modifying early-life soy intake could contribute to breast cancer prevention.”

Dr Giota Mitrou, executive director of research and policy at the World Cancer Research Fund, said the study “adds to our understanding of how exposures across the life course may shape cancer risk”. The study also “raises the possibility that breast tissue may be particularly susceptible to dietary influences during specific developmental windows”, but added that further research is needed into dietary patterns in different population groups.