Sex can affect participation, engagement, and adherence in trials.

1Health Services Research Unit, School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK; 2Health Services Research Unit and Health Economics Research Unit, School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK; 3Rowett Institute of Nutrition and Health, School of Medicine, Medical Science and Nutrition, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK; 4Scottish Collaboration for Public Health Research and Policy (SCPHRP), Centre for Population Health Sciences (CPHS), University of Edinburgh, Edinburgh EH8 9DX, UK; 5Centre for Midwifery, Maternal and Perinatal Health, Faculty of Health and Social Sciences, Bournemouth House, Bournemouth University, Bournemouth BU1 3LH, UK; 6NMAHP Research Unit, Unit 13, Scion House, Stirling University Innovation Park, Stirling FK9 4NF, UK; 7Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow G12 9QQ, UK