Background Accumulating evidence suggests that television (TV) viewing is associated with cardio-metabolic risk, but little is known about how this relationship unfolds over the life course. This study employs a life course epidemiological framework by examining the potential cumulative effect of frequent TV viewing during adolescence and young adulthood on the prevalence of metabolic syndrome in mid-adulthood; and whether TV viewing during adolescence constitutes a sensitive period for the development of the metabolic syndrome in mid-adulthood.

Methods We used data from the Northern Swedish Cohort, a nationally representative cohort comprising 855 participants (80% of the baseline sample). Data were collected during 1981–2008 and analysed in 2013. Logistic regression was applied to examine the associations between TV viewing at ages 16, 21 and 30 years, and the metabolic syndrome at age 43 years.

Results Cumulative frequent TV viewing was associated with subsequent prevalence of the metabolic syndrome after adjustment for potential confounders (p for trend=0.026). Watching ‘several shows a day’ compared with ‘one show/week’ or less at age 16 years was associated with the metabolic syndrome at age 43 years after adjustment for later exposure (TV viewing at ages 21 and 30 years) and potential confounders (OR 1.86, 95% CI 1.06 to 3.27).

Conclusions The number of life periods of frequent TV viewing during adolescence and early adulthood influenced cardio-metabolic risk in mid-adulthood in a dose-dependent manner, corresponding to a cumulative risk life course model. Additionally, TV viewing in adolescence may constitute a sensitive period for the metabolic syndrome in mid-adulthood.