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Unlock This CourseHave you ever wondered why you feel sleepy at night and alert during the day? Or why you feel terrible after a long flight to another country? The answer lies in your biological rhythms - natural cycles that control many of your body's functions. These internal clocks have evolved over millions of years to help us survive and thrive.
Biological rhythms are like invisible conductors orchestrating the symphony of your body. They control when you sleep, when you wake up, when you feel hungry and even when your body temperature rises and falls throughout the day.
Key Definitions:
Circadian Rhythms: 24-hour cycles (sleep-wake, body temperature)
Ultradian Rhythms: Less than 24 hours (REM sleep cycles, hormone pulses)
Infradian Rhythms: More than 24 hours (menstrual cycle, seasonal changes)
Deep inside your brain, about the size of a grain of rice, sits your body's master clock - the suprachiasmatic nucleus (SCN). This remarkable structure contains about 20,000 neurons that work together to keep your body running on schedule.
Your SCN receives information about light and darkness through a special pathway from your eyes. When light hits your retina, signals travel directly to the SCN, telling it whether it's day or night. This information helps your body clock stay synchronised with the outside world.
Cortisol levels peak, body temperature rises, alertness increases. Your body prepares for the day ahead.
Peak alertness and coordination. Best time for physical and mental performance.
Melatonin production begins, body temperature drops, drowsiness increases.
Even without any light cues, your body clock runs on approximately a 25-hour cycle. The daily exposure to light helps reset it to exactly 24 hours - this process is called 'entrainment'.
Jetlag is what happens when you travel quickly across multiple time zones, leaving your internal body clock confused and out of sync. Imagine your body clock is set to London time, but you've just landed in New York. Your brain thinks it's midnight and time for sleep, but the local time says it's only 7pm!
When you fly across time zones, your body's internal clock doesn't instantly adjust to the new local time. This creates a mismatch between your internal rhythms and the external environment. The result? You feel tired when you should be alert, hungry at odd times and generally out of sorts.
Symptoms of Jetlag Include:
Flying East: Generally more difficult to adjust to. You're trying to go to bed earlier and wake up earlier than your body wants.
Flying West: Usually easier to adapt to. You're extending your day, which is more natural for most people.
A study of business executives who frequently travelled between London and New York found that those flying eastward took an average of 8 days to fully adjust their sleep patterns, while those flying westward took only 6 days. The executives reported decreased performance and increased errors during the adjustment period, highlighting the real-world impact of circadian rhythm disruption.
It's not just air travel that can disrupt your biological rhythms. People who work night shifts, rotating shifts, or irregular hours also experience circadian rhythm disruption. This affects millions of workers worldwide, from nurses and doctors to factory workers and security guards.
Shift workers must stay awake and alert when their body clock is programmed for sleep. This constant battle against their natural rhythms can lead to Shift Work Sleep Disorder (SWSD), affecting both their health and job performance.
Common Problems for Shift Workers:
Research in a major London hospital found that nurses working permanent night shifts showed adaptation after 2-3 weeks, with improved sleep quality and alertness. However, nurses on rotating shifts (changing between day and night shifts) never fully adapted, experiencing ongoing sleep problems and reporting more medical errors during their shifts.
Understanding biological rhythms isn't just academic - it has practical applications for managing jetlag and shift work challenges. Here are evidence-based strategies that actually work.
Expose yourself to bright light at the right times to help reset your body clock. Light in the morning helps you wake up earlier.
This natural hormone can help regulate sleep-wake cycles when taken at the right time (usually 30 minutes before desired bedtime).
Eating meals at local times helps your body adjust to the new schedule. Avoid large meals close to bedtime.
While shift work will always be challenging, certain strategies can help minimise the impact on your biological rhythms:
Modern technology offers new solutions: light therapy devices, sleep tracking apps and smart alarm clocks that wake you during lighter sleep phases. However, blue light from screens can disrupt melatonin production, so avoid devices before bedtime.
Not everyone's biological clock ticks at the same rate. Some people are natural "larks" (morning people), while others are "owls" (night people). These preferences, called chronotypes, are partly genetic and influence how severely jetlag and shift work affect different individuals.
Your chronotype affects when you naturally feel alert and when you feel sleepy. Morning larks typically adjust better to eastward travel and early morning shifts, while night owls cope better with westward travel and night shifts.
Factors Influencing Chronotype:
A study of over 700,000 people found that extreme night owls had a 10% higher risk of dying from any cause compared to morning larks. This highlights the importance of understanding and working with, rather than against, your natural biological rhythms.
Biological rhythms are fundamental to human health and wellbeing. Understanding how your internal clock works can help you make better decisions about travel, work schedules and daily routines. While we can't completely eliminate the challenges of jetlag and shift work, we can use scientific knowledge to minimise their impact.
Remember that your biological rhythms evolved over millions of years to help you survive in a world with predictable cycles of light and darkness. Modern life often conflicts with these ancient patterns, but by understanding and respecting your body's natural rhythms, you can improve your sleep, health and overall quality of life.