Adolescent Dietary Intake and Breast Cancer in Adulthood: A Systematic Review and Meta-Analysis.

Adolescence represents a key opportunity for breast cancer prevention, as the rapid proliferation of breast tissue during puberty creates a critical window of vulnerability for the development of cancerous cells. With increasing research on adolescent dietary factors and breast cancer risk, we conducted a systematic review and meta-analysis to summarize the associations between adolescent diet and risk of breast cancer in adulthood, as well as benign breast disease (BBD) and high mammographic breast density, which are markers for breast cancer. We searched Web of Science, Ovid MEDLINE, Cochrane CENTRAL and Embase for epidemiological studies assessing dietary intakes in adolescent girls (aged 10-18 years), published through 16 October 2024, with no language or time restrictions. Study quality was assessed using the Newcastle-Ottawa Scale and results were pooled using random-effects models. The review included 51 studies, mostly from the USA, with the majority relying on adult recall of adolescent diet, and only 20 studies assessed as high quality. Higher adolescent intakes of fruits and vegetables (RR: 0.90; 95% CI: 0.82, 0.99; n=3 studies), soy (RR: 0.67; 95% CI: 0.55, 0.82; n=3), dietary fiber (RR: 0.78; 95% CI: 0.67, 0.92; n=3), and vegetable fat (RR: 0.76; 95% CI: 0.66, 0.88; n=2) were associated with lower risks of breast cancer in adulthood. No significant associations were observed for meat and poultry, fish, processed meat/fish, eggs, dairy, milk, grains, alcohol, total fat, animal fat, and isoflavone. Additionally, greater consumption of dietary fiber (RR: 0.64; 95% CI: 0.50, 0.82; n=2) and vitamin D (RR: 0.77; 95% CI: 0.62, 0.95; n=2) during adolescence was associated with lower risks of BBD, while no dietary associations were observed for mammographic breast density. Our findings underscore the importance of both diet and timing in breast cancer prevention. Future well-designed prospective life course studies are needed to strengthen this evidence base. REGISTRY: This systematic review and meta-analysis was registered with PROSPERO (CRD42024532597). STATEMENT OF SIGNIFICANCE: To our knowledge, this is the first comprehensive review to review and quantify the association between adolescent intake of various dietary components and breast cancer risk in adulthood. Current dietary strategies for breast cancer prevention are largely informed by epidemiological evidence from studies involving adult populations. Our findings offer preliminary insights into potential pathways linking dietary exposures during adolescence to breast cancer development. We also identify critical gaps in adolescent research, emphasizing the need for continued high-quality research targeting the formative years to inform future prevention efforts.