This project aims to generate evidence on the causal effect of alcohol intake on breast cancer (BC) risk, identify effective

prevention strategies, and improve alcohol risks communication.

 

• Objective 1: To assess the effect of long-term hypothetical alcohol interventions on BC risk in Norwegian women.
• Objective 2: To estimate the average causal effects of replacing alcohol with non-alcoholic drinks on BC risk in Norwegian women.
• Objective 3: To examine the additive interaction of alcohol intake and menopausal hormone therapy (MHT) on BC risk, to quantify the burden of BC attributed to their joined effect.
• Objective 4: Assess the state of knowledge among the public and stakeholders, and initiate discussions about alcohol risk communication.

Breast cancer (BC) is the most common cancer among women in Norway and globally.

 

Alcohol intake is a well-established risk factor, with evidence supported by biological mechanisms. Methodological limitations of conventional observational studies obscure firm causal conclusions. Mendelian randomization that is less prone to confounding has not confirmed a causal effect ofintake of less than 2 drinks/day.

 

Public awareness of alcohol-BC link remains low. Current drinking guidelines and messages use vague language, which is often ineffective to encourage alcohol reduction. Modern causal inference methods like target trial emulation and g-formula offer more accurate estimates of risk from observational data but are not yet used in alcohol-BC research.

 

Moreover, the additive interaction of alcohol and MHT and their joint burden on BC risk is understudied. Robust evidence and identification of practical prevention strategies (e.g., replacing alcohol with non-alcoholic drinks) are needed to improve prevention, communication and awareness.

 

To address questions on alcohol and BC risk, the project uses data from the Norwegian Women and Health Study (NOWAC), a representative cohort with 2-4 repeated measurements of alcohol, lifestyle, and health data from over 170,000 women.

 

The project employs modern causal inference methods such as "emulated target trial" approach to mimic randomized controlled trials using observational data.

 

• Work Package 1 (WP) assesses BC risk under hypothetical alcohol interventions using the g-formula that properly addresses timevarying exposures and confounding.
• WP2 assesses the effect of replacing alcohol with non-alcoholic drinks on BC risk using substitution analysis and targeted maximum likelihood estimation.
• WP3 asses the joint effects of alcohol and MHT, examining additive interaction and quantifying BC cases attributed to their effect.
• WP4 focuses on public engagement and science communication, aiming to raise public awareness of alcohol-BC links through surveys, co-creation of messages with experts and the public, and dissemination via health campaigns.

This project will generate robust epidemiological evidence on the causal link between alcohol intake and BC risk, helping to identify high-risk groups and practical and effective strategies for prevention.

 

Using modern causal inference methods, it will strengthen the scientific foundation for drinking recommendations for both the general population and cancer survivors. It will also offer the first empirical insights into the benefits of substituting alcohol with non-alcoholic drinks and the additive effects of alcohol and MHT on BC risk. These findings may inform healthcare practices, including alcohol screening during MHT prescriptions.

 

The project supports the Norwegian National Cancer Strategy 2025-2035 by identifying effective prevention strategies and improving alcohol risk communication. A dedicated work package will engage the public and stakeholders, foster fact-based dialogue around alcohol and cancer, and improve risk communication. Long-term, the project may help reduce BC incidence and relieve healthcare burdens.

 

Project period: May 2026-May 2030.

The project is financed by the Norwegian Cancer Society and the Norwegian Breast Cancer Society through Pink Ribbon funding.