Abstract
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 y), 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 United States, with the majority relying on adult recall of adolescent diet, and only 20 studies were assessed as high quality. Higher adolescent intakes of fruits and vegetables [relative risk (RR): 0.90; 95% confidence interval (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, whereas 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. This systematic review and meta-analysis was registered with PROSPERO (CRD42024532597).