Can't stay up late, can't lose weight? It's true!

"I sleep through the spring without knowing the dawn, I hear birds singing everywhere, the sound of wind and rain comes at night, I wonder how many flowers have fallen."

"Spring is sleepy, autumn is tired, summer is dozing, and winter is sleepy and March is hard to wake up."

For a long time, people have had the impression that fat people are "sloppy, lazy and gluttonous". For fat people, "eating less and exercising more" seems to be an effective way to control weight.

There is another saying: Behind every fat person there is a selfish, lazy and greedy soul.

Sleeping after eating and eating after waking up seems to be a shortcut to "fatten up".

Some people even think that most fat people sleep well and like to sleep in.

From the above, we can see that to correct obesity, it seems that the right way is to let fat people get up earlier and sleep less.

Actually, this is not the case. Obesity is the result of multiple factors. Eating more and exercising less is certainly one of the main reasons. However, it has been discovered in recent years that sleep is closely related to obesity, and proper sleep is very beneficial to obesity!

The current sleep status of children in my country

A study with a sample size of 30,250 conducted in nine provinces in my country found that after entering school age, children's lack of sleep becomes more prominent and becomes more obvious with age. The average daily sleep time of children in my country is 9.2 hours for primary school students, 8.1 hours for junior high school students, and 7.1 hours for high school students, respectively. More than 70% of primary and secondary school students suffer from insufficient sleep, and the problem shows a downward trend with age.

At present, due to academic pressure and family environment, school-age children in my country often cannot get enough sleep, and generally tend to have insufficient sleep at night. Moreover, as they age, their sleep time tends to decrease.

The role of sleep in children's physiological health and physical development cannot be ignored. During sleep, the human body can not only get enough rest and regulate immune function, but also secrete a variety of hormones related to the body's normal physiological metabolism.

As school-age children face increasing academic pressure and poor study habits, they develop poor sleep habits, poor sleep quality, and shortened sleep time, which in turn leads to hormone disorders related to children's physiological metabolism and growth and development, and is also one of the important factors that exacerbate the occurrence and development of childhood obesity. In recent years, many studies have shown that both too short and too long sleep time in children are related to overweight and obesity.

If you don’t get enough sleep, you’ll get fat

The role of sleep in children's physical development cannot be ignored. Although there are differences in the subjects of previous studies and different standards for defining sleep time, so far, all systematic reviews and large-sample clinical studies have shown that sleep duration is related to children's body size and has a dose-effect relationship.

Meta-analysis and clinical studies at home and abroad support that short sleep duration is a risk factor for overweight and obesity, and reduced sleep duration is associated with an increase in body mass index or other obesity indicators. Insufficient sleep may cause changes in eating behavior and a decrease in energy expenditure, ultimately leading to energy imbalance and obesity, which may be related to changes in appetite-related hormone levels [2-4].

In addition, some studies have found that there are some gender differences between men and women: insufficient sleep is a risk factor for overweight and obesity in boys, but no similar findings were found in girls [5-6]. This suggests that boys are at a greater risk of overweight and obesity when they are sleep deprived than girls, but the reason for this difference needs further study.

Sleep more, get fatter

Insufficient sleep increases the risk of overweight and obesity in children, and some studies have also found that sleeping too long can also increase the risk of overweight and obesity in children.

A study on Chinese adolescents suggested that there is a U-shaped relationship between sleep duration and overweight/obesity in children. Taking 7-9 hours of sleep as a reference, the odds ratios for sleep <5 hours, 5-7 hours, and more than 9 hours were (OR=1.26, 95% CI: 1.05-1.51), (OR=1.06, 95% CI: 1.00-1.11), and (OR=1.27, 95% CI: 1.14-1.42), respectively. This result suggests that both too short and too long sleep duration are risk factors for overweight and obesity [2].

Mechanism of Proper Sleep in Preventing Obesity

Sleep plays an important role in energy balance. When sleep time is reduced, it is easy to cause fatigue and daytime sleepiness, which reduces the amount of activity during the day. The reduction of daytime physical activity will lead to a decrease in sleep quality, entering a vicious cycle. Reduced activity is an important factor causing childhood obesity.

Reduced sleep can change the levels of leptin, ghrelin, insulin, cortisol, interleukin-6, and growth hormone, etc. Changes in these hormones or factors can cause sympathetic nerve excitement in the brain, increase food intake, and further aggravate obesity symptoms.

The 2019 Beijing Children and Adolescents Metabolic Syndrome Cohort Study found that the effect of shorter sleep duration on childhood obesity compared with longer sleep duration was related to the modification of the leptin pathway. Sufficient sleep duration in childhood is important for early prevention of obesity, especially for people with genetic predisposition [4].

How much sleep is appropriate?

Throughout a person's life cycle, different age groups need different amounts of sleep, and the appropriate amount of sleep for children of different ages is also different. The Chinese Nutrition Society has made recommendations on children's sleep time: ensure adequate sleep time, 10 hours a day for primary school students, 9 hours for junior high school students, and 8 hours for high school students. In 2020, the National Health Commission, the Ministry of Education and other six departments jointly issued the "Implementation Plan for the Prevention and Control of Obesity in Children and Adolescents", which recommends that children and adolescents should be guaranteed sleep time.

If you can't stay up late, you can't lose weight. This is not just talk, it's true.

Sleeping too long or too short is a risk factor for childhood obesity. We should start from society, family, school and other aspects to strengthen health education and guidance, publicize the importance of sleep, change children's bad living habits, and ensure adequate sleep to prevent the occurrence and development of obesity.

References:

[1] Jiang Liu, Yan Shuangqin, Geng Menglong et al. Association between nighttime sleep duration and bedtime and obesity in preschool children. Chinese Journal of Preventive Medicine 2018; 52: 1146-1151.

[2]Wu J, Wu H, Wang J et al. Associations between Sleep Duration and Overweight / Obesity: Results from 66,817 Chinese Adolescents. Sci Rep 2015; 5: 16686.

[3]Yoong SL, Chai LK, Williams CM et al. Systematic review and meta-analysis of interventions targeting sleep and their impact on child body mass index, diet, and physical activity. Obesity 2016; 24: 1140-1147.

[4]Fu J, Wang Y, Li G et al. Childhood sleep duration modifies the polygenic risk for obesity in youth through leptin pathway: the Beijing Child and Adolescent Metabolic Syndrome cohort study. International journal of obesity (2005) 2019; 1.

[5] Gong Qinghai, Li Hui, Wang Feng et al. Correlation between sleep and overweight and obesity among adolescents in Ningbo. Chinese School Health 2017.

[6] Wu Guobao. Sleep status and its correlation with overweight and obesity among middle school students in Urumqi. Chinese Journal of Child Health 2018; 26: 76-79.

Project source: Shanghai Science and Technology Commission Science Popularization Project Funding (Project No.: 21DZ2301800)

Author: Ruan Huijuan Niu Yang | Department of Clinical Nutrition, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine