Study: sleeping in artificial light can make you fat

Light from display screens in particular impairs sleep.

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iStock.com/Viacheslav Peretiatko

To prevent overweight and obesity, it is not only necessary to have healthy habits such as a balanced diet with enough relevant nutrients and physical activity. Other basic conditions like having the correct lighting in the bedroom must also be right, so that superfluous pounds or kilos do not creep in overnight. A US study has now made this clear. According to the study, artificial light not only disturbs sleep but can even make people fat. This is especially true for women, as scientists from the National Institutes of Health in the US state of North Carolina discovered.

They examined almost 44,000 women aged between 35 and 74 over a period of 5.7 years. None of the participants in the study had a history of cardiovascular disease or cancer or were pregnant. Furthermore, none of them were shift workers or so-called day sleepers. At the beginning of the study, the women had to provide information on their weight, height, waist and hip circumference and respective body mass index. They were also asked under what conditions they sleep: with a night light, with light shining in from outside, with light from a television in the room or completely without light. Five years later, the researchers compared the initial information with the data at the end of the study. As they themselves pointed out, the results of the study were based on the information provided by the participants and could not be checked. The authors of the study admitted that this represented a certain restriction.

Nevertheless, according to the authors, the findings of the study speak for themselves: women who slept without light or only by the glow of a small night light did not gain any weight in the five years following the start of the study. On the other hand, those participants who slept with light or while the television was on had a 17 per cent higher probability of gaining 5 kg in body weight. The likelihood of them being overweight therefore increased by 22 per cent if they slept under the glow of a night light, and the risk of becoming obese increased by 33 per cent compared to those who slept in the dark.

Artificial light disturbs duration and quality of sleep

After evaluating the data provided by their test subjects, the researchers from the National Institutes of Health concluded that basically the more light the test person had in her room during sleep, the greater was the risk of her gaining weight. It raises the question of how this can come about.

The scientists explained the connection with the fact that any form of artificial light in the room where one sleeps disturbs, if not stops, restful sleep. This is due to our genetic disposition: our internal biological clock is set to a 24-hour sleep-wake rhythm, the so-called circadian rhythm. This also corresponds to the natural light-dark cycle of day and night. If one prefers to sleep at night with light in the room, there is a danger that the light-dark rhythm, and thus also the sleep-wake cycle, is disturbed and the inner clock becomes out of sync. In this respect, many doctors believe sleeping in light is in principle less healthy. This is because if the biological clock is not ticking properly, the metabolism and hormone production also lose their rhythm. As darkness falls, the body increases the release of melatonin, the so-called sleep hormone. Instead, the body produces for example glucocorticoid, the stress hormone.

The authors of the US study, and not only them, attribute a negative influence of artificial light in particular on sleep: It is regarded as shortening the duration of sleep and having an adverse effect on its quality. The bluish light of display screens, such as smartphones or computers, is considered to be particularly harmful in this respect. Such artificial light in the bedroom leads to a less uniform sleep-wake cycle and shortens the duration of sleep, the scientists say. The study also found that this blue light causes sleep disturbances and more frequent interruptions to sleep at night.

All these factors lead to a significantly increased risk of weight gain and obesity. That`s why scientists at the National Institutes for Health in North Carolina recommend doing more for healthy sleep – by turning off all screens in good time, for example. This is also part of meaningful ‘sleep hygiene’, which facilitates healthy sleep and counteracts sleep disorders. As the US study shows, one then also prevents the risk of unwanted weight gain or even obesity.

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