Children who watch TV an increased number of hours between the ages of two and four years old risk larger waistlines by age 10.
A Canadian study found that every extra weekly hour watched could add half a millimetre to their waist circumference and reduce muscle fitness.
The study, in a BioMed Central journal, tracked the TV habits of 1,314 children.
Experts say children should not watch more than two hours of TV a day.
Researchers found that the average amount of television watched by the children at the start of the study was 8.8 hours a week.
This increased on average by six hours over the next two years to reach 14.8 hours a week by the age of four-and-a-half.
Every extra weekly hour spent by children in front of a TV could add 0.5 mm to their waist circumference and reduce muscle fitness
Fifteen per cent of the children in the study were watching more than 18 hours per week by that age, according to their parents.
The study said the effect of 18 hours of television at 4.5 years of age would by the age of 10 result in an extra 7.6 mm of waist because of the child’s TV habit.
As well as measuring waist circumference, the researchers also carried out a standing long jump test to measure each child’s muscular fitness and athletic ability.
An extra weekly hour of TV can decrease the distance a child is able to jump from standing by 0.36 cm, the study said.
The researchers said that further research was needed to work out whether television watching is directly responsible for the health issues they observed.
Dr. Linda Pagani, study co-author from the University of Montreal, said it was a warning about the factors which could lead to childhood obesity.
“The bottom line is that watching too much television – beyond the recommended amounts – is not good,” Dr. Linda Pagani said.
The American Academy of Pediatrics recommends that children aged over two should not watch more than two hours of television per day.
Dr. Linda Pagani added: “Across the occidental world, there have been dramatic increases in unhealthy weight for both children and adults in recent decades.
“Our standard of living has also changed in favor of more easily prepared, calorie-dense foods and sedentary practices.
“Watching more television not only displaces other forms of educational and active leisurely pursuits but also places them at risk of learning inaccurate information about proper eating.”
The study said that habits and behaviors became entrenched during childhood and these habits might affect attitudes to sporting activities in adulthood.
A new study findings presented at the European Congress on Obesity suggest that older obese men could shift excess weight by taking testosterone supplements.
In a study, hormone-deficient men were given testosterone supplements in a similar way to HRT for older women.
Men lost an average of 16 kg over five years when testosterone levels were increased back to normal.
But experts warn that supplements may not be the answer due to possible risks of prostate cancer and heart disease.
Prof. Richard Sharpe from the University of Edinburgh Centre for Reproductive Health said: “The notion that this is a quick fix for obese older men is, as always, simplistic. It is far more sensible and safer for men to reduce their food intake, reduce their obesity, which will then elevate their own testosterone.”
Men lost an average of 16 kg over five years when testosterone levels were increased back to normal
The findings announced at the conference also suggest that raising testosterone levels could reduce waist circumference and blood pressure.
Dr. Farid Saad, lead author of the study said: “We came across this by accident. These men were being given testosterone for a hormone deficiency – they had a range of problems – erectile dysfunction, fatigue and lack of energy.
“When we analysed the data we found that every year, for five years, they had lost weight. It may be that the increased testosterone restored their energy levels and led to a behavioural change of being more physically active.”
However, experts remain dubious. While some experts have linked low testosterone levels to a male “menopause”, with symptoms including changes in sleeping patterns, poor concentration, feeling worthless and anxiety, others have found to have no such link.
The study looked at 115 obese men aged between 38-83 years with low testosterone levels. They were injected with the hormone every 12 weeks to increase levels. The research, paid for by Bayer Pharma, a manufacturer of testosterone replacement therapy, found no increased risk of prostate cancer, a side-effect found in other studies.
The relationship between obesity and testosterone appears to be a vicious cycle. There are numerous studies showing that obesity, in particular abdominal obesity, is associated with reduced testosterone levels in men and a reduction in muscle.
With ageing, especially beyond 40-50 years, testosterone levels tend to decline slowly, which may predispose to abdominal obesity which will then further lower testosterone levels.