• Aviva A Musicus, Alyssa J Moran, Hannah G Lawman, and Christina A Roberto.
• Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, Massachusetts. Electronic address: aam231@mail.harvard.edu.
• Am J Prev Med. 2019 Dec 1; 57 (6): e181-e193.

IntroductionPolicymakers are interested in requiring chain restaurants to display sodium warning labels on menus to reduce sodium consumption. This study examined the influence of label design on consumers' hypothetical choices, meal perceptions, and knowledge.Study DesignFour sequential, randomized, controlled online experiments were conducted.Setting/ParticipantsAcross all 4 experiments, 10,412 sociodemographically diverse participants were recruited online through Survey Sampling International and Amazon Mechanical Turk.InterventionParticipants were randomized to view restaurant menus with either no sodium label (control) or 1 of 13 sodium warning labels that varied the text (e.g., "sodium warning" versus "high sodium"), icons (e.g., stop sign), and colors (red/black) used. Participants placed a hypothetical meal order and rated restaurant meal perceptions. Data were collected and analyzed in 2016-2019.Main Outcome MeasuresThe primary outcome was sodium content of hypothetical restaurant choices. Secondary outcomes included restaurant meal perceptions and sodium knowledge.ResultsIn Experiments 1-3, all warning labels reduced average sodium ordered across both restaurants (by 19-81 mg) versus controls, with some of the largest reductions from traffic light and stop sign labels, but results were not statistically significant. In a larger, preregistered replication (Experiment 4) testing traffic light and red stop sign labels versus control, traffic light and red stop sign labels significantly reduced average sodium ordered across both restaurants (-68 mg, p=0.002 and -46 mg, p=0.049, respectively). Warnings also significantly increased participants' knowledge of sodium content and perceived health risks associated with high-sodium meals compared with no label.ConclusionsTraffic light and red stop sign warning labels significantly reduced sodium ordered compared with a control. Warning labels also increased knowledge about high sodium content in restaurant meals. Designs with warning text are likely to improve consumer understanding.Copyright © 2019 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.

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