How Light Affects Your Sleep and Body Clock

When circadian rhythm drifts, people may experience:

• Delayed Sleep Phase Syndrome (DSPS): Bedtimes shift later and later, common in teenagers and young adults.
• Advanced Sleep Phase Disorder (ASPD): Bedtimes shift earlier, more common in the elderly.

The consequences go beyond fatigue. Insufficient sleep has been linked to high blood pressure, cardiovascular disease, poor blood sugar control in diabetics, and weakened immunity.

Research has shown that there is a strong genetic component to our individual circadian rhythms. Even within the normal population, there is a tendency for some people to be a “morning lark” or a “night owl” (Termed Chronotypes) from a young age, and Twin studies suggest that these Chronotypes are 50% heritable!

For those whose body clocks are out of sync, light therapy can be effective. A light box emits very bright blue light (10,000 lux, similar to full morning sunlight).

“This form of morning light or phototherapy brings forward an affected person’s sleep and wake times by a small duration each day. He will naturally feel sleepy earlier,” said Asst Prof Leow.

• For night owls: Use the light box for 30 minutes each morning for about two weeks.
• For early risers: Use it for 30 minutes around 7pm to help delay bedtime.

The treatment works best when paired with new habits: avoiding late-night screen time, limiting caffeine, and keeping a consistent sleep schedule.

“Over time, the person will rely less on the light box as his body clock resets. But he has to maintain good sleep hygiene,” said Asst Prof Leow.

At SGH’s Sleep Disorders Unit, about 70 per cent of patients with circadian rhythm disorders are teenagers and young adults with delayed sleep phase syndrome. “The youngest has been a secondary four student who had difficulties waking up in time for school, often missing school entirely,” he noted.

There is no such thing as a “perfect” circadian rhythm. Rather, an optimal sleep-wake cycle should be one that fits in with specific work, study and social demands and allows for sufficient time asleep. For some “night owls”, this may mean looking for jobs that allow for late mornings or working during the night e.g. financial analysts focusing on overseas markets.

Also, the body clock is not something that can be reset like an alarm clock. For most people, it takes about a day to delay or advance the body clock by 1hour under optimal conditions, and most people find delaying the clock (going to bed later) easier than the other way around.

For older adults, sleep often becomes lighter and more fragmented, with frequent toilet trips, aches and pains, or medications interfering.

“Going to bed and waking up early may be part of ageing, but this can be a problem for some. They may disturb their families when they wake at 4am. They also may not get to see their families often since the latter are already asleep when they reach home later at night,” said Asst Prof Leow.

Light therapy and melatonin supplementation at night can help here too, by shifting bedtime later to align better with family and social life.

The impact of poor sleep is more than just daytime drowsiness or poor performance. “The consequences of poor sleep can be more serious than just daytime sleepiness or poor school or work performance. Insufficient sleep can affect one’s health, such as by increasing blood pressure, and contributing to cardiovascular problems, poor blood sugar control in diabetics, and lowered immunity,” warned Asst Prof Leow.

• Get morning sunlight within the first hour of waking to synchronize your master body clock each day.
• Use dim, warm lighting in the evening to signal wind-down mode to stimulate natural melatonin release at night.
• Keep regular sleep and wake times, even on weekends to prevent your body clock from becoming disrupted.
• Limit screen use before bedtime as the blue light and intellectual stimulation can delay natural sleep onset.
• Speak to a sleep specialist if you suspect a circadian rhythm disorder.

Light is one of the most powerful influences on your body’s natural rhythms. By managing your exposure to sunlight and screens — and seeking help such as light therapy when necessary — you can reset your body clock, improve sleep quality, and protect your long-term health.

Ref: F26