Experts from the Massachusetts General Hospital established: due to lack of sleep in adolescents increases fat mass and blood pressure rises. This suggests that they increase the risk of cardiovascular diseases. 829 teenagers took part in the study. Volunteers wore the device for 7-10 days following their sleep and activity. risk factors for heart disease, stroke and diabetes experts also evaluated. They measured waist circumference participants, blood pressure, cholesterol levels and the degree of insulin resistance. 50 % adolescents asleep at least 7.4 hours. Total 2 % sleeping 8 or 9 hours a day (in accordance with the recommendations of age). The majority of the participants sleep efficiency was low. Long duration and high sleep efficiency were associated with lower blood pressure, cholesterol levels, lower waist circumference and amount of body fat.