The authors of this study of about 1000 individuals conclude that "Television viewing in childhood and adolescence is associated with overweight, poor fitness, smoking, and raised cholesterol in adulthood. Excessive viewing might have long-lasting adverse effects on health."

Association between child and adolescent television viewing and adult health: a longitudinal birth cohort study.

Hancox RJ, Milne BJ, Poulton R.

Dunedin Multidisciplinary Health and Development Research Unit, Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, PO Box 913, Dunedin New Zealand. bob.hancox@dmhdru.otago.ac.nz

http://www.ncbi.nlm.nih.gov/entrez/...t_uids=15262103

Lancet. 2004 Jul 17;364(9430):257-62