Daylight Saving Time: Does springing forward cause heart attacks?

What this episode covers

Every year we spring forward and lose an hour of sleep. But do we also lose a few heart cells? Some headlines claim that heart attacks spike by 24% after daylight saving time begins. In this episode we trace that number back to the research behind it—and what we find is more complicated than the headlines suggest. We examine a famous New England Journal of Medicine letter, a large international meta-analysis, and a massive modern U.S. registry study. Along the way we talk about incidence ratios, relative versus absolute risk, negative controls, and a haunting concept called harvesting. Plus: why bar charts are not for numerical data, why journalists love dramatic numbers, and how a bug collector helped invent daylight saving time.Statistical topicsIncidence ratios / incidence ratesMeta-analysisNegative controlsRelative risk vs absolute riskStatistical vs practical significanceStatistical SleuthingMethodological morals“A bump in time isn’t always a bump in total.” “If you already know the story you want to tell, you can always find a number to tell it.”  ReferencesBourke, India. “An obsessed insect hunter: The creepy-crawly origins of daylight saving.” BBC Future, March 31, 2024. https://www.bbc.com/future/article/20240308-how-first-suggestions-of-daylight-savings-time-was-inspired-by-insectsFox-Skelly, Jasmin. “How Daylight Saving Time Affects Your Health.” BBC Future, October 25, 2025. https://www.bbc.com/future/article/20251024-how-daylight-saving-time-affects-our-healthHurst A, Morfeld P, Lewis P, Erren TC. Daylight Saving Time Transitions and Risk of Heart Attack. Dtsch Arztebl Int. 2024;121(15):490-496. doi:10.3238/arztebl.m2024.0078Janszky I, Ljung R. Shifts to and from daylight saving time and incidence of myocardial infarction. N Engl J Med. 2008;359(18):1966-1968. doi:10.1056/NEJMc0807104Jiddou MR, Pica M, Boura J, Qu L, Franklin BA. Incidence of myocardial infarction with shifts to and from daylight savings time. Am J Cardiol. 2013;111(5):631-635. doi:10.1016/j.amjcard.2012.11.010Mellour, Richard. “The builder who changed how the world keeps time.” BBC Future, March 11, 2016. https://www.bbc.com/future/article/20160310-the-builder-who-changed-how-the-world-keeps-timeRymer JA, Li S, Chiswell K, et al. Daylight Savings Time and Acute Myocardial Infarction. JAMA Netw Open. 2025;8(9):e2530442. Published 2025 Sep 2. doi:10.1001/jamanetworkopen.2025.30442https://graph2table.com/Kristin and Regina’s online courses: Demystifying Data: A Modern Approach to Statistical Understanding  Clinical Trials: Design, Strategy, and Analysis Medical Statistics Certificate Program  Writing in the Sciences Epidemiology and Clinical Research Graduate Certificate Program Programs that we teach in:Epidemiology and Clinical Research Graduate Certificate Program Find us on:Kristin -  LinkedIn & Twitter/XRegina - LinkedIn & ReginaNuzzo.com(00:00) - Intro (05:03) - Strange history of daylight saving time (16:06) - Swedish NEJM study (19:14) - Incidence ratios explained (22:13) - What the Swedish study actually found (31:11) - Absolute vs relative risk (34:27) - Harvesting effect (40:10) - 2024 Meta-analysis (45:37) - Large modern US study (55:23) - Where the “24% increase” came from (59:16) - Wrap-up

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