Implemented during World War I to save energy, changing clocks for daylight saving time seems to be a blessing in the fall and an inconvenience in the spring, when we lose an hour. But researchers say their latest study suggests rolling the clocks forward may cause more than sleep disruption; it may also accelerate cardiac events in some individuals.

This research comes at a time when experts are debating whether daylight saving time is needed anymore. Some experts have questioned whether it does in fact save energy, while others have wondered whether it may have more negative health effects than simply making us feel groggy.

Dr. Amneet Sandu, lead author and cardiology fellow at the University of Colorado, Denver, notes that we experience daylight saving time changes twice a year, which prompted the research team to investigate how the hour lost or gained impacts our body's natural rhythm.

They present their research at the American College of Cardiology's 63rd Annual Scientific Session, and their study is published in the journal Open Heart.

To conduct their investigation, the team used Michigan's BMC2 database, which they explain collects data from every non-federal hospital in the state. The data helped them identify admissions for heart attacks requiring intervention between January 2010 and September 2013.

In total, there were 42,060 hospital admissions in the analysis, and total daily admissions were adjusted for seasonal and weekday variations. They did this because heart attack rates peak in the winter and decrease in the summer.

The team notes that the rate of heart attacks is also higher on Mondays and lower at the weekend.

Heart attacks increased after losing an hour, decreased after gaining an hour

Results showed that the Monday after we turn the clocks forward saw a 25% increase in the number of heart attacks, compared with other Mondays of the year. The team says this trend remained true even after they accounted for seasonal variations.

Interestingly, the researchers found that in the fall when we turn our clocks back and gain an hour, there was a 21% decrease in the number of heart attacks experienced on the first Tuesday.

Dr. Sandhu says their findings suggest the time changes increase cardiac event risk for those particularly susceptible:

"What's interesting is that the total number of heart attacks didn't change the week after daylight saving time. But these events were much more frequent the Monday after the spring time change and then tapered off over the other days of the week. It may mean that people who are already vulnerable to heart disease may be at greater risk right after sudden time changes."

He notes that though heart attacks historically occur most frequently on Monday morning, when they compared hospital admissions the Monday before the start of daylight saving time with the Monday after the time change for 4 years in a row, they found a consistent 34% increase in heart attacks from one week to the next.

In detail, there were 93 heart attacks on the Monday before rolling the clocks forward and 125 on the Monday after.

Study could enable hospital staff to be better prepared for surges

The team says they are unsure of exactly what might be driving the variation in heart attack timing after the time change.

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Feeling groggy after daylight saving time? New research suggests tiredness may not be the only downside; heart attacks spiked on the Mondays following the time change.

However, Dr. Sandhu says they have a theory, explaining: "Perhaps the reason we see more heart attacks on Monday mornings is a combination of factors, including the stress of starting a new work week and inherent changes in our sleep-wake cycle."

He adds that all of these changes are compounded by getting 1 less hour of sleep, and this suggests hospitals should increase staff on the Monday following the clock change.

"If we can identify days there may be surges in heart attacks, we can be ready to better care for our patients," he says.

Though the study involved a large sample size, there were some limitations. It only used data from one state, for example, and it only included heart attacks that needed percutaneous coronary intervention, which means it excluded patients who died prior to getting help.

To improve on future research, Dr. Sandhu says it would be a good idea to compare their findings with heart attack rates in Hawaii and Arizona, two states that do not have daylight saving time. He also says more research is needed to fully understand the role of circadian rhythms on heart health.

He concludes by saying:

"We know from previous studies that a lack of sleep can trigger heart attacks, but we don't have a good understanding of why people are so sensitive to changes in sleep-wake cycles. Our study suggests that sudden, even small changes in sleep could have detrimental effects."

Medical News Today recently reported on a study that suggested an enzyme - known as CK1epsilon - lowers the ability for our bodies to adapt from a light to dark environment. Researchers from that study suggest blocking this enzyme could help humans exposed to shift-work or long-haul air travel adapt to body clock changes.