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Sleeping with a light on could lead to obesity

Sleeping with a light on could lead to obesity

Monday 17 June 2019

A recent study has revealed that women who are exposed to artificial light at night (ALAN) are at risk of gaining weight and becoming obese.

The data was collected from women enrolled in the Sister Study programme, which is made up of American women who have sisters with breast cancer. The aim of the Sister Study is to research the causes of breast cancer.

The research to determine the effect of light exposure took data from 43,722 women aged between 35 and 74. These women had to complete questionnaires about their health and lifestyle every 2 years from when they signed up (between 2003 and 2009) to the study’s culmination in 2015.

The responses were categorized into 4 groups based on what light source they had when sleeping. These categories were: no light when sleeping, a small nightlight, light outside the room, a light or TV left on in the room when sleeping. The category each women belonged to was then cross referenced with the difference in their Body Mass Index (BMI) and hip & waist circumference measurements from when they signed up and finished the survey.

The results found that women that left the TV or light on in the room whilst sleeping had a 17% higher risk of gaining 5Kg or more compared to women who slept in total darkness. Additionally, they also had a 13% higher risk of increasing their BMI by 10%. According to Dr. Yong-Moon Mark Park who was one of the lead investigators in the research these conclusions also held their ground when taking into consideration other factors such as diet, exercise and inadequate sleep.

The study has received a lot of media attention in the UK leading to the NHS weighing in on the hot topic. The NHS acknowledged the potential correlation between light exposure and weight gain in women. However, they stated that the results don’t prove that light directly causes weight gain. They also said that if there was a direct relation between light and gaining weight it would likely be due to the impact that poor quality sleep has on the metabolic process and the ability to gain weight.


  1. Association of Exposure to Artificial Light at Night While Sleeping with Risk of Obesity in Women.

  2. Artificial light during sleep puts women at risk of obesity .

  3. What the NHS says about claims your bedroom lighting could be causing you to gain weight .


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