The more hours people in their 30s spend watching television each day, the higher the likelihood that they will have a greater body mass index and bigger waist circumference five years later, a 15-year study has found.
This association did not hold for people in their middle age, indicating that young adulthood is an important time to intervene and promote less television viewing.
"We were quite surprised to find that television viewing was associated with subsequent obesity for young adults, but not for the middle aged," said lead author Anthony Fabio, assistant professor of epidemiology at the University of Pittsburgh Schools of the Health Sciences in Pennsylvania, US.
"This suggests that middle aged adults may differ from young adults in how they respond to the influence of TV viewing," Fabio noted.
The researchers analysed data from 3,269 adults.
For 15 years starting in 1990, the participants reported their television viewing habits and had their waist circumference measured and their body mass index (a measure of weight and height that can indicate obesity) calculated every five years.
The more time participants spent watching television when they were approximately 30 years old, the more likely they were to be obese five years later, compared to their peers who spent less time in front of the television.
The researchers suspect many potential reasons for the association, including that young adults may be more likely to snack during television viewing and consume unhealthy food due to their greater susceptibility to the seduction of junk food advertising on television.
The researchers found that participants were more likely to eat healthier foods as they aged.