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Nov. 3, 2023

Ask the expert: You cannot replace a lack of sleep with coffee

After turning our clocks back an hour when daylight saving time ended on Nov. 5, many of us struggled to adjust to the time change. We reached for more coffee to help. But, new research from an MSU professor shows that an extra cup of coffee will not offset the transition.


Kimberly Fenn is a professor of cognition and cognitive neuroscience in the Department of Psychology in MSU’s College of Social Science. Fenn and her students who work in MSU’s Sleep and Learning Lab found that while caffeine may help keep you awake, there is no substitute for sleep when it comes to complex thinking. Fenn answered questions about what you should know about caffeine and sleep.

Responses are excerpts from an article published in The Conversation.

Kimberly Fenn is a professor of cognition and cognitive neuroscience in the Department of Psychology in MSU’s College of Social Science. She also leads MSU’s Sleep and Learning Lab, which provides students with research opportunities. Courtesy photo.

What is daylight saving time and why do we have it?

Daylight saving time is designed to increase the amount of natural daylight during the summer months. On the second Sunday in March, we shift our clocks forward, which results in the sun setting an hour “later,” effectively prolonging the light period by one hour. [On Nov. 5, we shifted] our clocks back because [that was] the end of daylight-saving time.

The idea of shifting the clocks was first proposed back in the 19th century by a New Zealand entomologist. Germany was the first country to adopt daylight saving time in 1916 to conserve fuel during World War I. The United States adopted the practice in 1918. The justification for shifting the clocks seems to be energy conservation, although there is no consistent data that supports significant energy savings. The shift has also been promoted to increase outdoor activities in the spring and summer months, the rationale being that people are more likely to go for a walk or run if it is still light outside.

Does sleep deprivation impair our cognition?

For many years, scientists have known that sleep deprivation reduces the ability to maintain attention. When asked to monitor a computer screen and press a button whenever a red dot appears — a simple task — sleep-deprived participants are much more likely to have lapses in attention. They don’t notice a bright red dot and fail to respond within a half-second. These lapses in attention are due to a buildup in pressure to sleep and are more common at points in the 24-hour circadian cycle when the body expects to be sleeping.

Research investigating the effect of sleep deprivation on more complex types of thinking has shown somewhat mixed results. So, my team and I sought to determine how keeping people awake for one night affected different types of thinking. We had participants perform various cognitive tasks in the evening before randomly assigning them to either go home and sleep or stay awake all night in the laboratory. The participants who were permitted to sleep returned in the morning and everyone completed the cognitive tasks again.

Along with impairments in attention, we also found that sleep deprivation led to more placekeeping errors. Placekeeping is a complex ability that involves following a series of steps in order without skipping or repeating. This would be similar to following a recipe to bake a cake from memory. You wouldn’t want to forget to add eggs or accidentally add the salt twice.

Can caffeine reverse deficits due to sleep deprivation?

Next, we set out to test different ways to potentially make up for a lack of sleep. What would you do if you did not sleep enough last night? Many people would reach for a cup of coffee or an energy drink.

One 2022 survey found that over 90% of the American adults sampled consume some form of caffeine daily. We wanted to see whether caffeine would help maintain attention and avoid placekeeping errors after sleep deprivation.

Interestingly, we found that caffeine improved the ability to pay attention in sleep-deprived participants so well that their performance was similar to people who slept all night. Giving caffeine to people who had a full night of sleep also boosted their performance. So, caffeine helped everyone maintain attention, not just those who did not sleep. This result was not surprising, as other studies have had similar findings.

However, we found that caffeine did not reduce placekeeping errors in either the sleep-deprived group or the group that slept. Thus, caffeine may help you stay awake and feel more alert, but it likely won’t help you with tasks that require complex thought. In other words, if you are sleep deprived, caffeine may help you stay awake and play Candy Crush, but it likely will not help you ace your algebra exam.

How does daylight saving time affect sleep, and do we need more sleep?

On average, most Americans need more sleep. The shift to daylight saving time in the spring causes individuals to effectively lose an hour of sleep. This has widespread consequences.

Following the March shift, there is a significant increase in car accidents and fatal car accidents due to sleep deprivation, circadian misalignment and changes in illumination during peak driving hours. In addition, there is a significant increase in the number of heart attacks on the Monday following the March shift. The fall shift is less dangerous because individuals get an extra hour of sleep.

In addition to losing an hour of sleep, the March shift works against your internal circadian clock. If you have ever traveled across multiple time zones, you have likely noticed that it is easier to travel westward than eastward. That is, it is easier to travel from New York City to San Francisco than from San Francisco to New York. This is because the circadian clock is approximately 24 hours, but for most people, their internal clock is actually a bit longer than 24 hours. Because of this, it is much easier to stay awake a few hours longer in the evening (like if you travel from New York to California) than it is to fall asleep (and wake up) a few hours earlier. This is evident in typical sleep patterns; on the weekends, individuals tend to stay up later and wake up later than they do during the week. This explains why it tends to be more difficult to wake up on Monday morning; you are effectively resetting your clock back to the 24-hour cycle.

How many hours of sleep do we need?

The average adult needs seven to nine hours of sleep per night. Approximately a third of American adults report sleeping less than seven hours per night and do not get sufficient sleep each night. In short, sufficient sleep is essential to your mind and brain, and there is simply no substitute for sleep.

Could any changes be made to daylight saving time?

Each state has the option to observe daylight saving time. All do, except Arizona and Hawaii. All counties in Indiana observe the shift, but the state is split such that some counties are in the Eastern time zone and others are in the Central time zone.

In 2022, the Senate passed a bill to end the twice-yearly shift in time, but the bill was stalled because senators could not agree on whether to stay on permanent daylight-saving time or standard time. The bill has been reintroduced this year and now proposes to keep daylight saving time permanent. This is widely supported by sleep and circadian scientists.

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