Social jet lag

                          Social jet lag 
Vocabulary: 
in sync；disparity =divergence ；harmonize ；integrate；correlate 
realign ；coordinate ；deviate ；reorient ；rebalance ；


From Monday to Friday, many of us have an early start and a long day. By the time we've gone to bed and managed to fall asleep, we've been woken up by the alarm to do it all again. Come the weekend, and we're totally exhausted. We sleep in way past our usual wake-up time just to stay in sync enough to start again on Monday.
Welcome to social jet lag. That's the term for the disparity between our working-week sleeping pattern, when our sleep times relate to our responsibilities, and the weekend, when we can wake when we choose. And depending on what type of person you are, the difference can be significant.
For night owls - those whose natural rhythm is to wake and go to bed later - there can be significant health-related issues, according to a recent study published by Taylor and Francis Group online. The study concludes the further the divergence between working-week and weekend sleep times, the greater the health issues – including a higher risk of heart disease and other metabolic problems. And because so many jobs and tasks start early, night owls are effectively forced into harmonizing with the early birds.
So what can night owls do: force themselves to integrate by sacrificing their lie in? 'It's the worst thing you can do' says Professor Till Roenneberg, professor of chrono-biology at the Institute of Medical Psychology at Ludwig-Maximilian University in Munich. This is because people's sleep pattern is half determined by genetics. The other half correlates with their age and environment. Getting less sleep is unlikely to realign your genetic tendencies.
Our bodies evolved to coordinate with the rise and fall of the Sun. We should feel sleepy as the light dissipates. But modern life, with its artificial light and modern devices, such as computers and smartphones, means we have deviated. Now we are exposed to more light for longer periods of time, keeping our bodies awake longer. For night owls, who already tend to sleep later, this delays things even further.
One solution, beyond changing society's early-start tendencies, is to reorient our body clock by manipulating our exposure to light By taking more sunlight in the morning and minimizing the amount of artificial light we are exposed to in the evening – particularly on electronic devices - we can re-balance our bodies to feel sleepy earlier. It's far from easy, but better that than losing your whole weekend to sleep.