Matthew Walker on health: what the evidence says · JRE #1109
“Full across 70 countries twice a year and it's cool daylight savings time. Now in the spring when we lose an hour of sleep. We see a subsequent 24% increase in heart attacks. What in the fall in the ottoman we gain an hour of sleep does a 21% decrease in heart attacks”
What the evidence says
Walker's 24%/21% figures trace to a single 2014 study (Sandhu, Seth & Gurm, Open Heart) that analyzed heart-attack admissions in one U.S. regional database, the Blue Cross Blue Shield of Michigan Cardiovascular Consortium PCI registry, March 2010 to September 2013, not a dataset spanning 70 countries. The paper's introduction notes that DST is observed by over 1.5 billion people in 70 countries, which appears to be the source of Walker's '70 countries' framing, but the study itself covers only Michigan. It did find a 24% rise in daily AMI counts on the Monday after the spring-forward change (p=0.011) and a 21% drop on the Tuesday after falling back (p=0.044), but the authors' own conclusion is that DST 'impacts the timing of presentations for AMI but does not influence the overall incidence of this disease', total weekly AMI counts did not differ significantly after either transition. So the specific percentages are accurately stated, but Walker's claim that they come from a 70-country study misattributes the scope and overstates it as a change in overall heart attack risk rather than a shift in timing within the week.