Semiannual Time Changes Linked to Accidents, Heart Attacks

As people turn their clocks back an hour on November 3 to mark the end of daylight saving time and return to standard time, they should remain aware of their sleep health and of potential risks associated with shifts in sleep patterns, according to a University of Calgary psychology professor who researches circadian cycles.

Notably, previous studies have shown that the twice-yearly time change is associated with increases in car accidents and workplace injuries, as well as heart attacks and strokes, owing to disrupted sleep, said Michael Antle, PhD, head of the psychology department at the University of Calgary and member of the Hotchkiss Brain Institute at the Cumming School of Medicine.

In an interview with Medscape Medical News, Antle explained the science behind the health risks associated with time changes, offered tips to prepare for the shift, and discussed scientists’ suggestion to move to year-round standard time. This interview has been condensed and edited for clarity.

Why is it important to pay attention to circadian rhythms?

Circadian rhythms are patterns of physiologic and behavioral changes that affect everything inside the body and everything we do, including when hormones are secreted, digestive juices are ready to digest, and growth hormones are released at night. The body is a carefully coordinated orchestra, and everything has to happen at the right time.

When we start messing with those rhythms, that’s when states of disease start coming on and we don’t feel well. You’ve probably experienced it — when you try to stay up late, eat at the wrong times, or have jet lag. Flying across one or two time zones is usually tolerable, but if you fly across the world, it can be profound and make you feel bad, even up to a week. Similar shifts happen with the time changes.

How do the time changes affect health risks?

The wintertime change is generally more tolerable, and you’ll hear people talk about “gaining an hour” of sleep. It’s better than that, because we’re realigning our social clocks — such as our work schedules and school schedules — with daylight. We tend to go to bed relative to the sun but wake up based on when our boss says to be at our desk, so an earlier sunset helps us to fall asleep earlier and is healthier for our body.

In the spring, the opposite happens, and the time change affects us much more than just one bad night of sleep. For some people, it can feel like losing an hour of sleep every day for weeks, and that abrupt change can lead to car accidents, workplace injuries, heart attacks, and strokes. Our body experiences extra strain when we’re not awake and ready for the day.

What does your research show?

Most of my work focuses on preclinical models to understand what’s going on in the brain and body. Because we can’t study this ethically in humans, we learn a lot from animal models, especially mice. In a recent study looking at mild circadian disruption — where we raised mice on days that were about 75 minutes shorter — we saw they started developing diabetes, heart disease, and insulin resistance within in a few months, or about the time they were a young adult.

Oftentimes, people think about their sleep rhythm as an arbitrary choice, but in fact, it does affect your health. We know that if your human circadian clock runs slow, morning light can help fix that and reset it, whereas evening light moves us in the other direction and makes it harder to get up in the morning. 

Some people want to switch to one year-round time. What do you advocate? 

In most cases, the standard time (or winter time) is the more natural time that fits better with our body cycle. If we follow a time where we get up before sunrise or have a later sunset, then it’s linked to more social jet lag, where people are less attentive at work, don’t learn as well at school, and have more accidents.

Instead of picking what sounds good or chasing the name — such as “daylight saving time” — we need to think about the right time for us and our circadian clock. Some places, such as Maine in the United States, would actually fit better with the Atlantic time zone or the Maritime provinces in Canada, whereas some parts of Alberta are geographically west of Los Angeles based on longitude and would fit better with the Pacific time zone. Sticking with a year-round daylight saving time in some cities in Alberta would mean people wouldn’t see the sun until 10:30 AM in the winter, which is really late and could affect activities such as skiing and hockey.

The Canadian Society for Chronobiology advocates for year-round standard time to align our social clocks with our biological clocks. Sleep and circadian rhythm experts in the US and globally have issued similar position statements.

What tips do you suggest to help people adjust their circadian clocks in November?

For people who know their bodies and that it will affect them more, give yourself extra time. If your schedule permits, plan ahead and change your clocks sooner, especially if you’re able to do so over the weekend. Don’t rush around while tired — rushing when you’re not ready leads to those increased accidents on the road or on the job. Know that the sun will still be mismatched for a bit and your body clock will take time to adjust, so you might feel out of sorts for a few days.

Antle reported no relevant financial relationships. 

Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape, MDedge, and WebMD.