The purpose of this investigation is to assess the role of the genetic and environmental factor on circadian system, in free living conditions by the use of a female twin population. With the results from this study, the investigators expect to advance in the understanding of the role of the endogenicity of the circadian system variables such as temperature, activity, sleep and timing of food intake as the main cause of the coincidence of the rhythms. However, the investigators expected that some parameters are still dependent on environment to a relevant extent and, hence, amenable to change through external interventions.

Twin studies are a classic in the analysis of the relative contribution of genetic and environmental factors to behavior and other phenotypes. These models are most often used to separate genetic from environmental causes in the family resemblance methodology. These models based on twins have been previously carried out in chronobiology. In fact, during the years 1993 and 1994, Paul Linkowski et al., performed two relevant studies on the circadian system to analyze the relative contributions of hereditary and/or environmental factors of cortisol secretion and blood pressure, respectively, and concluded that genetic factors control some of the characteristics of cortisol and diastolic blood pressure circadian rhythmicity. The heritability of other circadian markers has also demonstrated such as morningness- eveningness (44%), sleep-related variables have also pointed to a relevant role of genetics with heritability estimates of sleep duration between 17% and 55%. However, to the investigators knowledge, the heritability of other relevant chronobiological markers, measured in free living conditions such as body temperature, actigraphy and sleep has not been studied.

These goals will be achieved through a specific approach:

• Observational (Aim 1): To study the potential effect of the genetic and environmental factor in the circadian system health in order to improve the chronobiological therapies in the clinical practice (n=106).

IInclusion Criteria:

• Body Mass Index: >19 kg/m2
• Age: between 18 and 70 year of age
• Caucasian

Exclusion Criteria:

• Receiving treatment with thermogenic, lipogenic, or contraceptive drugs
• Diabetes mellitus, chronic renal failure, hepatic diseases, or cancer diagnosis
• Bulimia diagnosis, prone to binge eating
• Undergoing treatment with anxiolytic or antidepressant drugs

All participants are voluntarily in the Murcia Twin Register in Spain. All participants are from the Spanish city of Murcia, located on the Southeast coast of the Mediterranean Sea.