Why sleeping with the TV on could cause weight gain

By Sally Robertson, B.Sc.Jun 11 2019Reviewed by Kate Anderton, B.Sc. (Editor)

Exposure to artificial light at night while sleeping may be a risk factor for weight gain and the development of obesity, according to a study recently published in JAMA Internal Medicine. The study findings suggest that lowering artificial light exposure at night (ALAN) might be a useful intervention for obesity prevention.

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A high-calorie intake and sedentary behaviors are generally considered to be the main contributors to the obesity epidemic and these are currently the most common targets in obesity prevention strategies. However, a growing body of evidence suggests that ALAN may also be a contributor.

Artificial light has been shown to affect circadian rhythm

Over recent decades, increasing trends in light pollution have paralleled the rise in obesity prevalence in the U.S. Findings from animal studies also suggest that night-time light exposure may directly influence melatonin signaling and the circadian rhythm in ways that could lead to weight gain. In rodents, ALAN has been associated with suppression of genes involved in the circadian rhythm and altered feeding patterns that cause weight gain.

However, few studies have looked at the association between ALAN and obesity in humans.  Research has mainly been limited to studies looking at shift workers who are exposed to a lot more occupational light than non-shift workers.

A small number of studies have pointed towards a link between ALAN while sleeping and weight gain, but firm conclusions could be drawn due to limitations such as small sample groups, cross-sectional designs and a lack of adjustment for potential confounders such as diet and physical activity.

Proving an association between artificial light and weight gain

Now, epidemiologist Dale Sandler from the National Institutes of Health and colleagues have investigated the association between ALAN while sleeping and risk for weight gain and obesity using data from a large prospective cohort of US women involved in the Sister Study.

More than five years of follow-up data were available for 43,722 women (aged 35 to 74 years) from all 50 states in the U.S and Puerto Rico who were enrolled between July 2003 to March 2009.

None of the women were shift workers, day-time sleepers or pregnant at baseline and none had a history of cardiovascular disease or cancer. Sensitivity analyses and additional multivariable analyses were performed to adjust for potential mediating factors such as sleep duration and quality, diet, and physical activity.

Sandler and team report that among the 43,772 women (who had a mean age of 55 years), ALAN while sleeping was positively associated with an increased obesity prevalence at baseline, as determined by measures of body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR), and waist-to-height ratio (WHtR). ALAN whilst sleeping was also associated with 19% increased risk for incident obesity.

Compared with women who were not exposed to ALAN while sleeping, women who slept with a television or light on in the background were 17% more likely to gain 5kg or more in weight, 13% more likely to have a 10% or more increase in BMI, 22% more likely to become overweight and 33% more likely to become obese.

Artificial light at night while sleeping was significantly associated with increased risk of weight gain and obesity, especially in women who had a light or a television on in the room while sleeping.”

The associations did not seem to be explained by sleep duration/quality or other potential mediators such as diet and physical activity.

The authors say the findings suggest that artificial light exposure at night should be addressed in obesity prevention discussions:

“Further prospective and interventional studies could help elucidate this association and clarify whether lowering exposure to ALAN while sleeping can promote obesity prevention,” they conclude.

Artificial light contains blue wavelengths

Prior to the advent of artificial lighting, the sun was the main source of light and people generally spent the evening and night-time in darkness. Now, across most of the globe, people’s evening environment is illuminated by energy-efficient lighting and electronics with screens such as televisions or laptops.

This increases exposure to blue wavelengths of light, which is beneficial in the daytime, boosting attention span, mood and reaction times. However, studies have shown that this blue-light exposure can be disruptive during the night-time.

Scientists know that light exposure suppresses the secretion of the hormone melatonin, which is involved in regulating the circadian rhythm. Even exposure to dim light has an effect and exposure to light at night is one of the reasons people suffer from poor sleep.

While any type of light exposure can affect melatonin secretion and the circadian rhythm, exposure to blue wavelengths at night is known to have a stronger effect.

Researchers at Harvard University and colleagues performed an experiment comparing the difference in effect between 6.5 hours of blue light and green light exposure. The study showed that exposure to blue light suppressed melatonin for approximately double the amount of time the green light did, as well as causing twice as much shift in circadian rhythm.

How to prevent weight gain associated with ALAN

• Ensure that any lights being used as night lights are dim red lights. Red light is the least powerful at suppressing melatonin and shifting circadian rhythm
• Avoid looking at bright screens from three hours prior to going to bed
• If working night shifts, wear glasses that block blue light and if using electronic devices at night, install an application that filters blue-green light.
• Ensure plenty of exposure to bright light throughout the day. This will improve night-time sleep, as well as enhancing mood and alertness levels during the day.