This study aims to investigate

1. whether sleep extension results in improvements of endocrine and metabolic markers of obesity and diabetes in obese teenagers,
2. the relationship between habitual sleep quality and duration and markers of obesity and diabetes in lean and obese teenagers.

Inclusion of 13 obese teens. Duration : 1 week of screening period + 1 week of intervention: habitual/extended sleep length + 1 week of intervention: extended/habitual sleep length. A wash out period of at least 3 months will be required between the two interventions.

Inclusion of 13 non obese healthy teen controls for measuring reference sleep duration and physiology level. Duration for these group: 1 week of screening period + 1 week of habitual sleep length

Inclusion Criteria:

• Male or female over 15 and under 18 year-old.
• Teenager with normal weight or stage 2 obesity, according to international standards (WHO)
• Post-pubescent teenagers (menstruation for girls and stage 4-5 of Tanner scale for boys)
• Teens with an social security
• Girl with negative urine pregnancy test

Exclusion Criteria:

• Active smoker (interview)
• Refuse consent (parents or teen)
• Addiction such as coffee, drug…(interview)
• Medicinal treatment that may influence sleep and measured variables (interview)
• Obesity diagnosis : less than 1 year (interview)
• Concomitant diseases : renal or hepatic failure, iron deficit, diabetes, endocrinal pathology, hypertension
• Anxiety (Spielberg>56), , depression (CDI>19).
• Mild or sever insomnia (ISI>15), poor sleep quality (PSQI >10), excessive sleepiness (Epworth>10, sleep) length>9 hour), extreme circadian typology (Horne et Ostberg from 70 to 86 or 16 to 30)
• Blood sample taken within the last two months before inclusion
• Mild or severe sleep apnoea or excessive leg movements according to EEG analysis