It kills people.

Daylight savings time practices have been linked to increases in deadly traffic accidents, workplace injuries, medical errors and overall mortality.

In 2018, researchers in Spain penned a letter that was published in the journal Epidemiology regarding a link between deadly car accidents and daylight savings shifts. After collecting data from capital cities in Spain between 1990 and 2014, the researchers found a 30% increase in fatal traffic accidents on the day clocks sprang forwards. On the day clocks fell backwards, they saw an increase of 16%.

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One of the serious health concerns related to time shifts is acute myocardial infarction, or heart attack. Researchers in Italy wrote a 2018 review published in the journal Internal Emergency Medicine investigating daylight savings' potential effects on heart health. They reviewed seven existing studies from the United States and Europe looking at more than 80,000 cases of acute myocardial infarction. They found an increase, from 4% to 29%, in heart attacks after clocks sprang forwards.

Incidence of stroke may also increase after a clock shift. For a 2016 study published in the journal Sleep Medicine, researchers in Finland investigated the connection. They analysed more than 3,000 hospitalizations from 2004 to 2013 that occurred in the week following seasonal clock changes. They next compared those cases to a control group of 11,000 expected hospitalizations. The findings showed that hospitalizations for ischaemic stroke, the most common type, increased by 8% in the two days following a daylight savings shift. When looking at the whole week post-shift, the increase was 3%. The association was stronger for people assigned female at birth and those who were older.