Obesity and the Biological Clock: When Times Are out of Joint

May 10, 2012

Science Daily/Ludwig-Maximilians-Universitaet Muenchen (LMU)

Urgent appointments, tight work timetables and hectic social schedules structure modern life, and they very often clash with our intrinsic biological rhythms. The discrepancy results in so-called social jetlag, which can damage one's health. Among other effects, it can contribute to the development of obesity, as a new LMU study shows.

"Our surveys suggest that in Western societies two thirds of the population are burdened with a significant discrepancy between their internal time and the demands imposed by school and work schedules and leisure stress," says LMU chronobiologist Professor Till Roenneberg, who coined the term "social jetlag" to describe the phenomenon. If the rhythms dictated by our lifestyles are persistently out of phase with our biological clock, the risk of illness, such as high blood pressure and even cancer, rises.

Tired -- around the clock A team of researchers led by Roenneberg has now shown that social jetlag also contributes to another growing health problem, particularly in countries with a Western lifestyle -- obesity. Individuals who are overweight are at increased risk for serious metabolic diseases, such as diabetes. Many factors, in addition to excessive consumption of energy-rich foods, play a role in the development of obesity, and one of them is a lack of sleep. In persons who get too little sleep, the perception of hunger is perturbed, often leading to overeating.

And it is not just sleep duration that is important here. The LMU team has also found that social jetlag shows a significant association with increased body-mass index (BMI). The BMI, which is based on a quantitative relationship between weight and height, is used as a measure of body fat, and varies depending on age and sex.

Individuals with BMIs above the normal range are regarded as being overweight or obese. The results of the new study strongly indicate that a lifestyle that conflicts with our internal physiological rhythms can promote the development of obesity.

Moreover, it appears that the incidence of social jetlag is itself increasing, perhaps as a consequence of a general reduction in sleep duration."The ongoing debate on the usefulness of daylight-saving time (DST) should take note of our findings," remarks Roenneberg. "Just like conventional school and work schedules, DST disrupts our biological clock and subjects us to more social jetlag with all its consequences."

http://www.sciencedaily.com/releases/2012/05/120510132637.htm

Lack of morning light keeping teenagers up at night

February 27, 2010

Science Daily/Rensselaer Polytechnic Institute

The first field study on the impact of light on teenagers' sleeping habits finds that insufficient daily morning light exposure contributes to teenagers not getting enough sleep.

"As teenagers spend more time indoors, they miss out on essential morning light needed to stimulate the body's 24-hour biological system, which regulates the sleep/wake cycle," reports Mariana Figueiro, Ph.D., Assistant Professor and Program Director at Rensselaer Polytechnic Institute's Lighting Research Center (LRC) and lead researcher on the new study.

"These morning-light-deprived teenagers are going to bed later, getting less sleep and possibly under-performing on standardized tests. We are starting to call this the teenage night owl syndrome."

Disrupting Biological Rhythms

The problem is that today's middle and high schools have rigid schedules requiring teenagers to be in school very early in the morning. These students are likely to miss the morning light because they are often traveling to and arriving at school before the sun is up or as it's just rising. "This disrupts the connection between daily biological rhythms, called circadian rhythms, and the earth's natural 24-hour light/dark cycle," explains Dr. Figueiro.

In addition, the schools are not likely providing adequate electric light or daylight to stimulate this biological or circadian system, which regulates body temperature, alertness, appetite, hormones and sleep patterns. Our biological system responds to light much differently than our visual system. It is much more sensitive to blue light. Therefore, having enough light in the classroom to read and study does not guarantee that there is sufficient light to stimulate our biological system.

"According to our study, however, the situation in schools can be changed rapidly by the conscious delivery of daylight, which is saturated with short-wavelength, or blue, light," reports Dr. Figueiro.

The new research has applications for more than 3 million shift workers and Alzheimer's patients who suffer from lack of a regular sleep pattern.

Studies have shown that this lack of synchronization between a shift worker's rest and activity and light/dark patterns leads to a much higher risk of cardiovascular disease, diabetes, seasonal depression and cancer over decades.

As evidenced in prior studies by Dr. Figueiro, light therapy can also be used to improve sleep in Alzheimer's patients, who usually display uneven sleep patterns. "By removing light at certain times of day, and giving light at other times, you can synchronize the sleep/wake patterns of Alzheimer's patients with the light/dark pattern, providing them with more consolidated sleep," says Dr. Figueiro.

http://www.sciencedaily.com/releases/2010/02/100216140305.htm