Sleep, Metabolism, Weight Gain

Is Your Alarm Clock Making You Fat?

Wynne Parry, LiveScience Senior Writer
Date: 10 May 2012
Alarm Clock
CREDIT: Alarm clock image via Shutterstock

In the industrialized world, a conflict between two opposing forces — biology and the alarm clock — is helping to make people fat, new research suggests.

A discrepancy between the natural timing of sleep and work or school schedules leads to sleep deprivation, since people forced into schedules unnatural to them don’t get enough sleep. And survey data indicates people with larger discrepancies are more likely to carry extra weight, according to the researchers.

“We are biological beings, and we have a biological clock, and what society — and I don’t mean the bad guys, I mean all of us — is ignoring is the biological clock,” said study researcher Till Roenneberg of the University of Munich. “We think we can do whatever we want with the social clock.”

There is a well-established link between sleep and metabolism. Previous studies have linked shorter sleep to obesity, and some have even linked longer sleep to obesity, although this link is less well established, said Jamie Zeitzer, an assistant professor at Stanford University who studies circadian rhythms and sleep. Zeitzer was not involved with the current study.

Different people need different amounts of sleep; this is a separate phenomenon from discrepancy in sleep timing, or as Roenneberg calls it, social jetlag. He and colleagues measured the timing discrepancy by looking at changes in the timing of the midpoint of a person’s night sleep between work and free days.

Other research has pointed to health hazards, from accidents to diabetes and obesity, associated with shift-work schedules, which move work into the nighttime hours.

“If you are awake at night, there is a good reason from an evolutionary perspective, something has to be going on,” Zeitzer said.

As a result, the body behaves as if it is going to need more energy, and people who are awake at night crave higher-fat and sugary foods, and have a greater appetite, he said.

Roenneberg points out that a gene linked to the amount of sleep people need, ABCC9, also plays a role in energy metabolism, or how fast our body uses energy from the food eaten and, in turn, a person’s appetite.

Alarming results

Roenneberg and his colleagues drew on survey data from more than 65,000 people, primarily in central Europe, on their waking and sleep behavior during work and free days. The results were published online May 10 in the journal Current Biology.

Their analysis indicated that for each hour of sleep discrepancy someone experienced, they were 33 percent more likely to have a high body mass index (BMI, or an indicator of body fatness), Roenneberg said. (Someone with a BMI of 25 is considered overweight,greater than 30 is considered obese.)

However, the effect wasn’t uniform. Sleep discrepancy did not explain variations in body mass among those with a normal BMI; however, it was positively associated with increasing weight among those with a higher-than-normal body mass, in the overweight and above range.

This split doesn’t interfere with the overall conclusion that more discrepancy is associated with more weight, Zeitzer said.

An owl’s world

The survey showed that the weekly loss of sleep is worse for some people, namely, the “night owls” who wake up and go to sleep later. But while work times have stayed relatively constant, the modern world is shifting our natural body clocks later, Roenneberg said.

Our body clocks use light to set themselves; however, the indoor light under which many of us spend most of our days is much dimmer than natural light. As a result our body clocks are pushed later, causing us to wake up and go to sleep later in the day, he said.

To address the problem, Roenneberg, who is also the author of “Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired” (Harvard University Press, 2012), recommends making work times more flexible, a move he said could make employees happier and more productive, while reducing health-care costs.

Roenneberg said he coined the term “social jetlag” to compare the discrepancy between social and biological time. However, unlike travel jetlag, social jetlag doesn’t go away with time, he points out. Zeitzer takes issue with the term, because it implies a biological change not addressed in the research.


Body Odor and Personality Traits

Some Personality Traits Affect How You Smell

Rachael Rettner, MyHealthNewsDaily Staff Writer
Date: 02 December 2011 Time: 09:23 AM ET


Getting to know someone usually requires at least a little conversation. But a new study suggests you can get a hint of an individual’s personality through his or her scent alone.

Participants in the study assessed, with some degree of accuracy, how outgoing, anxious or dominant people were after only taking a whiff of their clothes. The study is the first to test whether personality traits can be discerned through body odor.

While the match-up between responses by the judges and the judged were not perfect, they do suggest that, when forming a first impression, we take into account a person’s smell, as well as visual and audible cues to their personality traits, the researchers said.

We not only express ourselves through our looks, “we also express ourselves with how we smell,” said study researcher Agnieszka Sorokowska, a doctoral candidate at the University of Wroclaw, in Poland.

The study will be published in an upcoming issue of the European Journal of Personality.

Personality smells

Sorokowska and colleagues asked 30 men and 30 women to don white cotton t-shirts for three consecutive nights. Participants could not use fragrances, deodorants orsoaps, and could not smoke or drink or eat odorous foods during the study. Participants also took a personality test.

Shirts from the “odor donors” were collected and rated by 100 men and 100 women. Raters were asked to smell the shirts (placed in non-transparent plastic bags) and evaluate five personality traits of the donors, on a scale of one to 10. Each rater assessed six shirts, and each shirt was assessed by 20 raters.

The judges’ ratings matched up with the self-assessments of the donors for three personality traits: extroversion (the tendency to be outgoing and sociable) neuroticism (the tendency to feel anxious and moody) and dominance (the urge to be a leader).

The matches were far from perfect. But the raters predicted the donor’s level of extroversion and neuroticism through smell about as accurately as participants in a different study predicted personality traits based on a video depicting a person’s behavior, Sorokowska said.

Judgments of dominance were most accurate in the case where an individual rater was assessing the odor of someone who was the opposite sex, suggesting such judgments are especially important when it comes to choosing a mate, the researchers said.

Odor and emotions

Extroversion, neuroticism and dominance are all traits that may, to some extent, be expressed physiologically, including through our emotions.

For instance, people who are neurotic may sweat more when they experience stress, which would modify the bacteria in their underarms and make them smell different, the researchers said.

Personality traits may also be linked with the secretion of hormones that could alter a persons’ scent. People who are high in dominance may have higher levels of testosterone, which in turn may modify their sweat glands, the researchers said.

The findings are preliminary and more studies need to be done to confirm the results, Sorokowska said. It’s not clear whether the same link would be found in other cultures known to have weaker body odors, Sorokowska said.