Breast cancer risk among postmenopausal women: Exploring existing interactions between BMI and reproductive factors (Fertile Years) in the Malmö Diet and Cancer Study
(2026) MPHN40 20232Social Medicine and Global Health
- Abstract
- Introduction: Breast cancer remains a global public health priority, with increasing incidence and mortality among postmenopausal women. While high body mass index (BMI) and reproductive history are established risk factors, the interaction between BMI and cumulative reproductive exposure, measured as fertile years, has not been thoroughly investigated. This study investigated the independent and interactive effects of BMI and fertile years on postmenopausal breast cancer risk.
Methods: Data from 6,628 postmenopausal women enrolled in the Malmö Diet and Cancer Study were analysed. BMI (kg/m²) was measured at baseline, and fertile years were estimated by subtracting the duration of pregnancy, breastfeeding, and miscarriage from the... (More) - Introduction: Breast cancer remains a global public health priority, with increasing incidence and mortality among postmenopausal women. While high body mass index (BMI) and reproductive history are established risk factors, the interaction between BMI and cumulative reproductive exposure, measured as fertile years, has not been thoroughly investigated. This study investigated the independent and interactive effects of BMI and fertile years on postmenopausal breast cancer risk.
Methods: Data from 6,628 postmenopausal women enrolled in the Malmö Diet and Cancer Study were analysed. BMI (kg/m²) was measured at baseline, and fertile years were estimated by subtracting the duration of pregnancy, breastfeeding, and miscarriage from the interval between menarche and menopause. Cox proportional hazards models estimated hazard ratios (HRs) for breast cancer risk. Interaction effects were evaluated on both multiplicative and additive scales using indices such as Relative Excess Risk due to Interaction (RERI), Attributable Proportion (AP), and Synergy Index (SI).
Results: Over approximately 29,000 person-years of follow-up, 625 breast cancer cases were identified (9.4%), yielding an incidence rate of 3.3 per 1,000 person-years. Independent associations between higher BMI and longer fertile years with breast cancer were observed, but not statistically significant. No significant multiplicative interaction was detected. However, a statistically significant additive interaction was found: RERI = 0.86 (95% CI: 0.14–1.58, p = 0.018) and AP = 0.39 (95% CI: 0.13–0.66, p = 0.003), indicating that 39% of the joint effect could be attributed to interaction.
Conclusion: This study provides novel evidence of a significant additive interaction between BMI and fertile years in postmenopausal breast cancer risk. These findings highlight the importance of assessing BMI and fertile years jointly in breast cancer risk evaluation. Future studies should explore underlying biological mechanisms and validate these results in diverse populations to inform targeted prevention strategies and improve the treatment options. (Less) - Popular Abstract
- Popular science summary
In 2020, more than two million cases of breast cancer were documented worldwide. In Sweden, breast cancer is the most common form of cancer among women. According to the most recent report from the National Board of Health and Welfare (Socialstyrelsen) in 2021, over 8,600 Swedish women were newly diagnosed with breast cancer, a 3.9% increase from previous years. Sadly, 16% of those women died with BC as the main cause.
Researchers have made a significant discovery in the ongoing fight against breast cancer. This discovery reveals how weight and reproductive history may interact to influence breast cancer risk in postmenopausal women. This study focused on a previously unexplored area: how body mass index (BMI), a... (More) - Popular science summary
In 2020, more than two million cases of breast cancer were documented worldwide. In Sweden, breast cancer is the most common form of cancer among women. According to the most recent report from the National Board of Health and Welfare (Socialstyrelsen) in 2021, over 8,600 Swedish women were newly diagnosed with breast cancer, a 3.9% increase from previous years. Sadly, 16% of those women died with BC as the main cause.
Researchers have made a significant discovery in the ongoing fight against breast cancer. This discovery reveals how weight and reproductive history may interact to influence breast cancer risk in postmenopausal women. This study focused on a previously unexplored area: how body mass index (BMI), a measure based on weight and height, and fertile years, the total time a woman has menstruated, might interact to affect breast cancer risk.
Interestingly, the study found that high BMI or longer fertile years did not significantly increase the risk of breast cancer. However, when these two factors were considered together, they revealed a meaningful interaction: their combined effect on breast cancer risk was stronger than when examined separately. This type of combined effect is called an additive interaction.
Understanding that BMI and reproductive history can interact in this way helps us better identify women who may be at higher risk. This insight is valuable for improving prevention strategies and developing more personalized health interventions for postmenopausal women.
This research adds an important piece to the puzzle of breast cancer and highlights the importance of looking at risk factors in combination, not just in isolation. It is a step forward in reducing breast cancer rates and improving outcomes for women around the world. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/student-papers/record/9221931
- author
- Belidi, Reham LU
- supervisor
- organization
- course
- MPHN40 20232
- year
- 2026
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9221931
- date added to LUP
- 2026-02-17 13:49:44
- date last changed
- 2026-02-24 16:22:35
@misc{9221931,
abstract = {{Introduction: Breast cancer remains a global public health priority, with increasing incidence and mortality among postmenopausal women. While high body mass index (BMI) and reproductive history are established risk factors, the interaction between BMI and cumulative reproductive exposure, measured as fertile years, has not been thoroughly investigated. This study investigated the independent and interactive effects of BMI and fertile years on postmenopausal breast cancer risk.
Methods: Data from 6,628 postmenopausal women enrolled in the Malmö Diet and Cancer Study were analysed. BMI (kg/m²) was measured at baseline, and fertile years were estimated by subtracting the duration of pregnancy, breastfeeding, and miscarriage from the interval between menarche and menopause. Cox proportional hazards models estimated hazard ratios (HRs) for breast cancer risk. Interaction effects were evaluated on both multiplicative and additive scales using indices such as Relative Excess Risk due to Interaction (RERI), Attributable Proportion (AP), and Synergy Index (SI).
Results: Over approximately 29,000 person-years of follow-up, 625 breast cancer cases were identified (9.4%), yielding an incidence rate of 3.3 per 1,000 person-years. Independent associations between higher BMI and longer fertile years with breast cancer were observed, but not statistically significant. No significant multiplicative interaction was detected. However, a statistically significant additive interaction was found: RERI = 0.86 (95% CI: 0.14–1.58, p = 0.018) and AP = 0.39 (95% CI: 0.13–0.66, p = 0.003), indicating that 39% of the joint effect could be attributed to interaction.
Conclusion: This study provides novel evidence of a significant additive interaction between BMI and fertile years in postmenopausal breast cancer risk. These findings highlight the importance of assessing BMI and fertile years jointly in breast cancer risk evaluation. Future studies should explore underlying biological mechanisms and validate these results in diverse populations to inform targeted prevention strategies and improve the treatment options.}},
author = {{Belidi, Reham}},
language = {{eng}},
note = {{Student Paper}},
title = {{Breast cancer risk among postmenopausal women: Exploring existing interactions between BMI and reproductive factors (Fertile Years) in the Malmö Diet and Cancer Study}},
year = {{2026}},
}