Our body clock is a small group of cells made up of unique "body clock" genes. These cells turn on and off and tell other parts of the body what time it is and what to do. In fact, most of our individual organs have their own internal body clock cells as well. Let’s take a look at how the internal body clock affects everything we do, and what the best time is for our body to engage in different daily activities.
Eating: Which Meal at What Time?
By far one of the trickiest topics to tackle is the optimal timing for eating. A quick search on Google reveals that there are as many viable diets as there are people. And yet, there are some great, general guidelines that we can follow.
A recent study in Cell Metabolism tried to find out, given all things equal, if timing actually makes a difference. Two groups of mice were put onto the exact same diet in terms of caloric intake. The only difference was that the first group had access to the food all day round, whilst the second group only for 8 hours during peak activity. The result according to the researchers was stunning:
So, limiting your food intake to your eight most active hours during the day could be a good idea. We can also dig a bit deeper into the optimal time for eating dinner in particular:
When You Should Eat Dinner
When it comes to dinner, eating late generally conflicts with our internal body clock because it’s starting to wind down and get ready for sleep. If we’re simply not set up to process the food we’re taking in, it’s probably not the best time for a big meal.
Nutritionist Linda Morgan from the University of Surrey wanted to see how efficient we are at processing food at night compared to in the morning. She conducted an experiment where participants were given the exact same foods at night and in the morning. Then she tested their blood glucose levels to see how much glucose their bodies were hanging onto.
Morgan says blood glucose levels indicate how efficiently your body is processing and storing glucose, and high levels of glucose in the blood after a meal can point out future risks like diabetes. Her experiment found that blood glucose levels after an evening meal were much higher than when the exact same meal was eaten earlier in the day. Morgan says this means we should try to get most of our calories earlier in the day, and have lighter, earlier evening meals when possible.
Sleeping: How Long and at What Time?
While some of us identify as night owls or morning larks, most of us actually have a fairly regular time when sleep benefits us most. Professor Jim Horne from Loughborough University says that we’re naturally designed to have two sleeps a day: a long one at night and another one in the early afternoon. Early afternoon is when our energy naturally dips lower than usual and we have a harder time focusing. In fact, according to an article in The New York Times, lots of cultures around the world break up their sleeping patterns:
We tend to be susceptible to micro sleeps around this time—that is, tiny moments where we nod off before shaking ourselves awake. This is our internal body clock saying it’s a good time to go to sleep, so if you’re planning a nap—slot it into this part of your day!
Although everyone is different to some degree, we actually all start out as morning people, and continue this way until around age 10. From ages 10–20 we start to sleep and wake up later and later until around 20 years old, when the pattern starts to reverse again and we start waking up earlier. Eventually, around age 55, we are going to sleep and waking up at roughly the same times we did when we were 10 years old.
So, age has a huge bearing on how our body clocks operate and what our optimal sleep times are. You’re probably familiar with how teenagers prefer to sleep in late and go to bed late, but it turns out it’s not just teenage laziness (although it is “just a phase,” since these tendencies lessen as we get older). From age 13-21 we get up later than any other time in our lives. Teenagers are biologically predisposed to sleep and wake later than anyone else. This means they’re often struggling with important cognitive work at school during their least optimal times. A study of school students’ memory function in the UK actually showed that students performed 9% better on the same type of memory tests in the afternoon as they did in the morning.
Another myth, similar to teenagers’ laziness when going to sleep is the fact that we need eight hours of sleep each night. Doctors famously eliminated that myth recently with a study showing that, we don’t in fact need that amount of sleep to reach our body’s best performance.
Exercising
When choosing a time of day to exercise, paying attention to your body clock can also improve results, as well as overall happiness through exercising. Physical performance is usually best, and the risk of injury least, from about 3 p.m. to 6 p.m., says doctor, an adjunct professor of biomedical engineering at the University of Texas, Austin, and lead author with doctor of “The Body Clock Guide to Better Health.”
Muscle strength tends to peak between 2 p.m. and 6 p.m. Muscle strength in the afternoon is up to 6% higher than at its lowest point in the day, which improves your ability to grip a club as well as lessening the risk of injury. Another boost for physical strength comes from the lungs, which function 17.6% more efficiently at 5 p.m. than at midday, according to a study of 4,756 patients led by Boris Medarov, an assistant professor of medicine at Albany Medical College in New York.
Hand-eye coordination is best in the late afternoon, making that a good time for racquetball or Frisbee. And joints and muscles are as much as 20% more flexible in the evening, lowering the risk of injury, Dr says. These body rhythms hold true regardless of how much you’ve slept or how recently you’ve eaten. In a 2007 study at the University of South Carolina at Columbia, 25 experienced swimmers did six time trials while sticking to an artificial schedule that controlled for variables like sleep and diet. The swimmers’ performance still varied by time of day, peaking in the evening and hitting bottom at around 5 a.m.
For runners, cyclists, and other endurance athletes, the morning is the worst performance time as well. Professor Greg Atkinson from Liverpool John Moores University says, “Almost every world record in track-and-field athletics and cycling events has been broken in the afternoon or evening.” This could be a result of our body temperature being at its peak later in the day, giving us a natural ‘pre-game warmup’ in a sense. Our receptiveness to pain is also lower in the afternoon, meaning we can push further in endurance sports. For other athletes, however, the morning could be the optimal performance time. Balance, for instance, is higher in the morning, so gymnasts might perform better then.
For those of us who aren’t chasing world records, afternoons certainly seem to be the best time for exercise. This can even help us sleep better:
Blood pressure is also a factor in our exercise routines. In the first three hours after we wake up, our blood pressure rises the most out of any point in the day. Our blood vessels open up more to allow for blood flow later in the day, our blood is not as sticky then and we have a natural drop in blood pressure in the afternoon. Exercising in the morning was found in an experiment to either increase blood pressure or not make a difference at all. In the evening, however, exercise was found to reduce blood pressure by 10–11%.
Working
The funny thing I found out about our best time for working is that in some ways, everything I thought I knew about being productive was wrong. It turns out that circadian rhythms really affect how we work as well, so we all have peaks and troughs in our physical and mental capacity to get work done. The interesting part of this is that the type of work we’re doing makes a difference to which time of the day we should choose to do it in. Here’s how it breaks down:
If you’re a morning lark, say, you’ll want to favor those morning hours when you’re feeling more fresh to get your most demanding, analytic work done. Using your brain to solve problems, answer questions and make decisions is best done when you’re at your peak, according to Scientific American:
For night owls, this is obviously a much later period in the day.
On the other hand, if you’re trying to do creative work, you’ll actually have more luck when you’re more tired and your brain isn’t functioning as efficiently. This sounds crazy, but it actually makes sense when you look at the reasoning behind it. It’s one of the reasons why great ideas often happen in the shower after a long day of work.
If you’re tired, your brain is not as good at filtering out distractions and focusing on a particular task. It’s also a lot less efficient at remembering connections between ideas or concepts. These are both good things when it comes to creative work, since this kind of work requires us to make new connections, be open to new ideas and think in new ways. So a tired, fuzzy brain is much more use to us when working on creative projects. This Scientific American article explains how distractions can actually be a good thing for creative thinking:
How Light Affects Our Body Clocks
Light is the single biggest external factor that affects our internal body clocks. Each of us has a slightly different internal time, which can range from a 22 hour cycle (a fast body clock, associated with morning larks) to a 25 hour cycle (a slow body clock, which night owls would have). The average is around 24.5 hours.
Sunlight helps us to adjust this internal time cycle each day to synchronize it with the world’s 24-hour cycle. It works like this: light hits the back of our eyes and travels into our brains, triggering the release of chemicals onto our body clock cells. This tweaks our internal time to be either slower or faster, making it exactly 24 hours.
This also means that the more sunlight your eyes receive during the day can affect your clock by slowing it down or speeding it up when you don’t want it to. If you get lots of light in the morning, this will speed up your body clock and help you wake up earlier. Getting lots of light in the afternoon and around sunset will do the opposite—slow down your body clock and help you stay up later into the night. This is probably the best trick I know for helping your body to adjust to a new timezone after flying halfway around the world, so it’s great to understand how it really affects our bodies!
Our dependence on light to keep our body clocks synchronized with the day’s 24 hour period is affected by our age, just like our sleep patterns are. As we get older, two main things happen that relate to this:
Our eyesight worsens, and we receive less light into our eyes
Our body clock becomes less active
Both of these things make our body clocks run slightly out of sync with the world. We start waking up a lot during the night, and often waking up far earlier than we’d like to. This is because the lack of light coming into our brains through our eyes gives a much weaker signal to our body clock cells to adjust them to a 24-hour period. And although we don’t lose any of our body clock cells, much fewer of them are actually active as we get older.
What’s also important to consider here is that the importance of lighting in your office or at home is tightly connected to the temperature in your workplace too. Make sure that both are aligned to get an even better focus on your activities.
There’s still hope, though. An experiment that tripled the amount of light dementia and alzheimer’s patients received during the day saw improvements in mood, better sleeping patterns, improved cognitive functions like memory and slower deteriorate of physical functions.
Some Other Cool Facts
There are some other areas that are affected by our body clocks that I found interesting. Here are some of my favorite facts that I found out, mostly from the BBC video mentioned at the top of this post (it’s pretty amazing—I’d recommend watching the whole thing if you have time!).
The Best Time to Drink
If you drink the same amount of alcohol at different points in the day, you will have the same blood-alcohol level, but it wil affect your brain differently. In the late afternoon/early evening our body clock is at its peak, so alcohol will have a lower effect on our cognitive ability. Lucky for us, this is right about the time for post-work drinks, so we can enjoy alcohol without it knocking us about like it would in the morning, or making us sleepy like it would at lunch.
The Best time for Medication
Adjusting the time of medication in a recent study damaged 5x fewer healthy cells and was 2x as effective at killing cancerous cells. Administering medications like chemotherapy which can kill healthy as well as diseased cells can be hugely affected by our body clocks. This study showed that if fewer of our healthy cells are active when the medication is administered, it will hurt less of them and be able to target the diseased cells better.
The Best Time to Have a Baby
More babies are born between 3-5 a.m. than any other time. Actually, this distinction is becoming less obvious as more and more births are affected by medical intervention, but the extremely relaxed state of our brains and muscles at this time and our lowered pain sensations mean not only is this a popular time for natural births to occur, but probably the best time you could choose as well.
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