Atakpa, Emma C.; email: e.c.atakpa@qmul.ac.ukBrentnall, Adam R.; email: a.brentnall@qmul.ac.ukAstley, Susan; email: Sue.astley@manchester.ac.ukCuzick, Jack; email: j.cuzick@qmul.ac.ukEvans, D. Gareth; orcid: 0000-0002-8482-5784; email: Gareth.Evans@mft.nhs.ukWarren, Ruth M. L.; email: rmlw2@cam.ac.ukHowell, Anthony; email: Anthony.Howell@manchester.ac.ukHarvie, Michelle; orcid: 0000-0001-9761-3089; email: michelle.harvie@manchester.ac.uk2021-07-012021-07-012021-06-29Cancers, volume 13, issue 13, page e3245http://hdl.handle.net/10034/625102From MDPI via Jisc Publications RouterHistory: accepted 2021-06-18, pub-electronic 2021-06-29Publication status: PublishedFunder: Cancer Research UK; Grant(s): C569/A16891, IS-BRC-1215-20007We evaluated the association between short-term change in body mass index (BMI) and breast density during a 1 year weight-loss intervention (Manchester, UK). We included 65 premenopausal women (35–45 years, ≥7 kg adult weight gain, family history of breast cancer). BMI and breast density (semi-automated area-based, automated volume-based) were measured at baseline, 1 year, and 2 years after study entry (1 year post intervention). Cross-sectional (between-women) and short-term change (within-women) associations between BMI and breast density were measured using repeated-measures correlation coefficients and multivariable linear mixed models. BMI was positively correlated with dense volume between-women (r = 0.41, 95%CI: 0.17, 0.61), but less so within-women (r = 0.08, 95%CI: −0.16, 0.28). There was little association with dense area (between-women r = −0.12, 95%CI: −0.38, 0.16; within-women r = 0.01, 95%CI: −0.24, 0.25). BMI and breast fat were positively correlated (volume: between r = 0.77, 95%CI: 0.69, 0.84, within r = 0.58, 95%CI: 0.36, 0.75; area: between r = 0.74, 95%CI: 0.63, 0.82, within r = 0.45, 95%CI: 0.23, 0.63). Multivariable models reported similar associations. Exploratory analysis suggested associations between BMI gain from 20 years and density measures (standard deviation change per +5 kg/m2 BMI: dense area: +0.61 (95%CI: 0.12, 1.09); fat volume: −0.31 (95%CI: −0.62, 0.00)). Short-term BMI change is likely to be positively associated with breast fat, but we found little association with dense tissue, although power was limited by small sample size.Licence for this article: https://creativecommons.org/licenses/by/4.0/mammographic densitybody mass indexweight lossbreast cancer riskbreast cancer preventionpremenopausalarticle2021-07-01