Introduction: Few studies exist on the effect of diet during different periods of life, on breast cancer risk later in life. Great differences existed in food consumption between the capital and rural areas in Iceland in the middle of the 20th century, with very high fish consumption in coastal areas.

Objectives: Our aim was to explore the effect of diet and residence during early life and midlife on breast cancer risk later in life.

Methods and data: We used data from the Reykjavik Study, a population-based Icelandic cohort of 10049 women born between 1907 and 1935, and examined the association of residence in early life, used as a proxy for dietary habits, and risk of breast cancer. To further explore this association, we also used food frequency data at different periods of life, including adolescence, from the AGES-Reykjavik cohort, a subgroup of the Reykjavik Study, established in 2002. Participants provided information on residence in early life. By linkage with the Icelandic Cancer Registry, information on breast cancer diagnoses was available throughout 2013. Adjustments were made for a series of potential confounders, including residence for dietary analysis.

Results: During a mean follow-up of 27.3 years, 744 women were diagnosed with breast cancer. We found a significant inverse association for breast cancer diagnosis among women who lived though the puberty period (20 years or more) in coastal villages compared with women residing in the capital area (HR = 0.74, 95% CI: 0.58, 0.94). In the subgroup analysis, we found that women with high fish consumption in midlife had lower risk of breast cancer in older age, compared with women with lower consumption, (OR = 0.60, 95% CI 0.38, 0,94). However, we did not observe a statistically significant association between high fish intake in adolescence and breast cancer (OR = 0.84, 95% CI 0.62 - 1.13).

Conclusions: Our results suggest that high fish consumption in early- to midlife may be associated with reduced risk of breast cancer.

Citation Format: Haraldsdottir A, Torfadottir JE, Valdimarsdottir UA, Aspelund T, Tryggvadottir L, Launer LJ, Harris TB, Gudnason V, Steingrimsdottir L. Early life residence, fish consumption and risk of breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-09-02.