Our bodies have evolved over millions of years to adjust to predictable patterns of light and darkness, helping to regulate sleep through our internal clock, or circadian rhythm.
We share this phenomenon with plants and diurnal animals: being active when the sun is up and inactive or sleeping when the sun goes down. Less than a century ago, man-made sources of light were relatively dim, such as that from a fire or candle, or from lamps fuelled by kerosene or gas.
Due to the invention of electric lighting, our exposure to bright light beyond daylight hours has increased significantly. You can also include exposure to light from electronic devices such as televisions, computer screens, mp3 players, tablet devices, smart phones, and even the light from a digital alarm clock. We are beginning to develop a better understanding of the impact that this extra light at night is having on our health, and our weight.
The circadian rhythm prepares our body for predictable events such as food availability and sleep. Disruption may trigger metabolic disturbances that affect our body shape.
The increased exposure to light at night during the 20th century coincides with the global increase in the prevalence of excess body fat.
Our internal clock relies on darkness to trigger the release of hormones which make us feel sleepy, preparing us to eventually fall asleep. But darkness also triggers hormones that perform a variety of other functions affecting weight, such as metabolism, appetite, mood and energy levels.
Light signals to the body that it’s time to wake up, and it can inhibit the secretion of the sleep-inducing hormone melatonin. Research suggests that reduced darkness and a lack of sleep can also alter the level of hormones which control appetite and eating behaviour.
A study reported in the Annals of Internal Medicine suggested that people who had less sleep experienced an increase in the hormone ghrelin that triggers hunger, reduces energy expenditure and promotes the retention of body fat.
Other research has shown that sleep disturbances caused by shift work are associated with an elevated BMI (body mass index) and adiposity (excess body fat).
Here are some tips to help minimise the impact of light at night on your weight.
Adopt a pre-sleep ritual – Dim the lights for an hour or two before bed to help your body prepare for sleep. Try to avoid the computer or television, and instead focus on having a bath or shower, brushing your teeth, meditating, listening to soft music, reading, or using aromatherapy with essential oils. This might also help you go to bed earlier and give your body more predictable patterns of light and darkness.
Make your bedroom dark – Do an audit of your bedroom to minimise any source of light exposure during sleep. Even small amounts of light at night (like the glow from your clock radio) may interfere with your body's internal clock. Cover up illuminated alarm clocks, and close your bedroom door if any light shines through it. Make sure your curtains and window coverings block as much light as possible, especially if you go to bed late. If this is too difficult, you can wear a sleep mask.
Drink the majority of your water earlier in the day - While it’s important to stay well hydrated, you don’t want it to interfere with your sleep. Avoid drinking too much liquid at night so you don’t get woken in up the early hours of the morning with the urge to go to the bathroom (and turn on the light). It also makes sense to visit the toilet just before bed, as this will reduce the chances that your sleep will be interrupted.
Don’t eat before bed – Eating later at night when you are less active may also disturb your internal clock. Try to finish eating at least 2 hours before going to bed to help your body prepare for sleep. This may improve your sleep quality by helping your body to focus on restoration instead of digestion. Brushing your teeth soon after dinner may help to fight the temptation to indulge in a late-night snack.
Here are some sleep-related articles that may help you sleep sound.
References available on request