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Does Artificial Light at Night Make People Fat?

A large number of things contribute to weight gain.

Some scientists even believe that night-time light, as insignificant as it may seem, could contribute to obesity over time.

Recently, an observational study examined the association of artificial, night-time light with obesity rates.

Today’s review provides a detailed summary of its findings.

Artificial Light

Artificial Light

Artificial Light at Night

Living in an urban area is associated with many risk factors for weight gain and obesity. One of them is artificial light-at-night (ALAN).

ALAN comes from a variety of sources, including highways, railways, street lights, buildings, industries and billboards.

The reason why ALAN may contribute to obesity is not entirely clear, but scientists believe that a disrupted body clock and reduced formation of night-time melatonin are involved (1, 2).

Previous studies also show that ALAN exposure may increase weight in laboratory animals (3, 4, 5, 6).

This is supported by two observational studies suggesting that increased light intensity in people’s bedrooms at night time may increase the risk of weight gain and obesity (7, 8).

However, until now, no studies have examined the association of ALAN with obesity rates on a population level.

Article Reviewed

This study examined the association of artificial, night-time light intensity with obesity rates.

Does artificial light-at-night exposure contribute to the worldwide obesity pandemic?

Study Design

This observational study examined the association of obesity rates with artificial, outdoor, night-time light pollution.

Night-time illumination in residential areas was assessed using recent satellite images from more than 80 countries.

Information on obesity rates was obtained from the World Health Organization (WHO) country-wide database.

When calculating the associations, the researchers statistically adjusted for potential bias by taking the following into account: population wealth (per capita GDP), level of urbanization, birth rate, food consumption and regional differences.

Bottom Line: This observational study examined the association of obesity rates with illumination at night.

Finding: Artificial, Night-Time Light Was Linked With Higher Obesity Rates

On a regional level, greater artificial, night-time light intensity was linked with higher obesity rates in more than 80 countries throughout the world.

Specifically, night-time illumination explained 72–73% of the regional differences in overweight and obesity rates in women and 67–68% in men.

Additionally, the researchers found that when artificial light-at-night levels increased from the minimum amount to the maximum, obesity rates appeared to increase, on average, by about 900% in Asia and 250% in the rest of the world.

Bottom Line: On a regional level, greater light pollution was associated with higher obesity rates.

How Can Night-Time Light Increase Weight Gain?

It is not entirely clear how increased artificial light-at-night might contribute to weight gain and obesity.

However, scientists have come up with several plausible theories:

  • Disrupted sleep quality: Night-time light exposure reduces sleep quality and may disrupt the body clock, potentially contributing to weight gain.
  • Increased appetite: Poor sleep and irregular sleeping patterns may disrupt the 24-hour fluctuations of appetite hormones.
  • Reduced calorie expenditure: Conversion of brown fat tissue into white fat tissue may slow down metabolic rate and calorie expenditure.

In a previous research review, we discussed the possible ways in which a disrupted body clock may affect weight gain and obesity.

Bottom Line: Being exposed to light while sleeping can reduce sleep quality. This may disrupt the body clock, potentially increasing appetite or reducing calorie expenditure.

Does Night-Time Light Really Make People Obese?

A variety of things contribute to weight gain and obesity.

On its own, it’s unlikely that night-time light exposure causes obesity, but when combined with other obesogenic factors it might increase the risk.

Other factors associated with an urban environment have also been linked with an increased risk of obesity. These include:

  • Traffic noise..
  • Traffic-related air pollution.
  • Increased fast food accessibility.

However, since most of the evidence is observational, it is difficult to isolate individual factors.

Although the human evidence is limited, controlled animal studies support the idea that night-time light may affect weight gain (9, 10).

Bottom Line: It is unlikely that artificial light-at-night has a large impact on obesity on its own. However, it might contribute to obesity when combined with other risk factors.

Limitations

The study’s main limitation was its observational design.

Simply put, it couldn’t prove that light exposure at night caused weight gain and obesity. Living in urban areas is associated with many other factors that may promote obesity.

Additionally, this was a population-level study, examining large populations of people rather than individuals.

Second, certain types of light are worse than others. For example, blue light suppresses melatonin formation more than other types of light. Distinguishing between different types of light could provide more accurate results.

Bottom Line: This was an observational study. For this reason, it doesn’t prove that night-time light exposure causes obesity.

Summary and Real-Life Application

In short, this study suggests that increased night-time light pollution in people’s bedrooms may increase the risk of obesity.

Night-time light is thought to disrupt the body clock, causing a hormonal imbalance that may affect appetite and/or calorie expenditure.

Due to its observational design, the study doesn’t provide any proof, but the findings are supported by controlled studies in animals.

Regardless of its possible effects on weight gain, a poor night’s sleep is unhealthy. Making sure your bedroom is dark at night may be something to consider.

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