A study of 815 healthy premenopausal women in Hong Kong reports a significant inverse correlation between soy protein intake in childhood and adolescence and adult mammographic density (MD).
MD – the proportion of epithelial and stromal tissue relative to total breast area – is a well-established marker and a strong predictor of breast cancer risk. [N Engl J Med 2007;356:227-236] While higher lifetime soy intake has been associated with lower adult MD, emerging evidence indicates that early-life soy exposures may play a more critical role than adult intake in determining long-term breast tissue composition. [Nutr Rev 2017;75:500-515; Cancer Epidemiol Biomarkers Prev 2009;18:1050-1059]
“This study aimed to examine the association between dietary soy intake during different life stages, including childhood, adolescence, young adulthood, recent intake, as well as cumulative intake, and adult MD in Chinese premenopausal women aged 35–45 years,” stated the researchers. [Nutrients 2026;18:1116]
Associations of recalled dietary soy intake through different life stages with MD were examined in a population of 815 healthy women (mean age, 40.9 years) recruited from the community. Dietary soy intake was assessed retrospectively using a questionnaire to capture consumption from 2–3 decades earlier. As such retrospective assessment is subject to recall error, audiovisual aids and a life history calendar administered by trained interviewers were employed to enhance memory.
The mean current soy protein intake was 10.25 g/day and isoflavone intake 22.0 mg/day. The respective values for age 6–12 years were 6.60 g/day and 15.28 mg/day, while those for age 13–18 years were 8.53 g/day and 19.01 mg/day, and for age 20–34 years, 9.48 g/day and 20.38 mg/day. The mean current MD value was 38.8 percent.
Regression analysis at different life stages on MD, after adjusting for age, waist circumference, height, number of live births, and physical activity, showed that soy protein intake during the ages of 6–12 and 13–18 years were significantly and inversely associated with MD (p<0.05). Women with consistently high early-life soy intake had 5.8–6.6 percent lower adjusted MD than those with consistently low intake.
Soy protein intake at 20–34 years of age was also inversely associated with MD, but did not reach a statistical level of significance, while no association was noted between MD and current soy protein intake. Similar findings were observed for the association between soy isoflavone intake through different life stages and MD.
“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,” commented first author of the study, Professor Suzanne Ho of the Faculty of Medicine, Chinese University of Hong Kong (CUHK).
“Early-life soy exposure may influence adult breast tissue composition and represents a potentially modifiable protective factor in breast cancer prevention. These findings carry important public health implications, particularly for populations experiencing dietary westernization,” concluded the researchers.