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. 2024 Jan 22;26(1):15.
doi: 10.1186/s13058-024-01766-0.

Differential patterns of reproductive and lifestyle risk factors for breast cancer according to birth cohorts among women in China, Japan and Korea

Salma Nabila  1   2 , Ji-Yeob Choi  3   4   5   6 , Sarah Krull Abe  7 , Md Rashedul Islam  7   8 , Md Shafiur Rahman  7   9 , Eiko Saito  10 , Aesun Shin  11   12 , Melissa A Merritt  13 , Ryoko Katagiri  14   15 , Xiao-Ou Shu  16 , Norie Sawada  14 , Akiko Tamakoshi  17 , Ritsu Sakata  18 , Atsushi Hozawa  19 , Jeongseon Kim  20 , Chisato Nagata  21 , Sue K Park  12 , Sun-Seog Kweon  22 , Hui Cai  16 , Shoichiro Tsugane  14   15 , Takashi Kimura  17 , Seiki Kanemura  19 , Yumi Sugawara  19 , Keiko Wada  21 , Min-Ho Shin  22 , Habibul Ahsan  23 , Paolo Boffetta  24   25 , Kee Seng Chia  26 , Keitaro Matsuo  27   28 , You-Lin Qiao  29 , Nathaniel Rothman  30 , Wei Zheng  16 , Manami Inoue  7 , Daehee Kang  11   12
Affiliations

Differential patterns of reproductive and lifestyle risk factors for breast cancer according to birth cohorts among women in China, Japan and Korea

Salma Nabila et al. Breast Cancer Res. .

Abstract

Background: The birth cohort effect has been suggested to influence the rate of breast cancer incidence and the trends of associated reproductive and lifestyle factors. We conducted a cohort study to determine whether a differential pattern of associations exists between certain factors and breast cancer risk based on birth cohorts.

Methods: This was a cohort study using pooled data from 12 cohort studies. We analysed associations between reproductive (menarche age, menopause age, parity and age at first delivery) and lifestyle (smoking and alcohol consumption) factors and breast cancer risk. We obtained hazard ratios (HRs) with 95% confidence intervals (CIs) using the Cox proportional hazard regression analysis on the 1920s, 1930s, 1940s and 1950s birth cohorts.

Results: Parity was found to lower the risk of breast cancer in the older but not in the younger birth cohort, whereas lifestyle factors showed associations with breast cancer risk only among the participants born in the 1950s. In the younger birth cohort group, the effect size was lower for parous women compared to the other cohort groups (HR [95% CI] 0.86 [0.66-1.13] compared to 0.60 [0.49-0.73], 0.46 [0.38-0.56] and 0.62 [0.51-0.77]). Meanwhile, a higher effect size was found for smoking (1.45 [1.14-1.84] compared to 1.25 [0.99-1.58], 1.06 [0.85-1.32] and 0.86 [0.69-1.08]) and alcohol consumption (1.22 [1.01-1.48] compared to 1.10 [0.90-1.33], 1.15 [0.96-1.38], and 1.07 [0.91-1.26]).

Conclusion: We observed different associations of parity, smoking and alcohol consumption with breast cancer risk across various birth cohorts.

Keywords: Asia; Background; Birth cohort; Breast cancer; Lifestyle factors; Reproductive factors; Women.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Participants selection
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