Children who eat fish once a week sleep better and have higher IQ scores, a new study suggests.

Researchers at the University of Pennsylvania in the US, said parents should consider simply changing the diets of youngsters rather than imploring them to go to bed.

Previous studies have shown that the omega-3 fatty acids found in fish can improve intelligence and sleep, and that better sleep improves IQ. But it is the first time all three have been linked together.

The scientists believe that it may be that the improved sleep produced by omega-3s is what is boosting IQ rather than the fatty acids themselves.

"Doing that could be a lot easier than nudging children about going to bed," said Professor Adrian Raine.

"If the fish improves sleep, great. If it also improves cognitive performance, like we've seen here, even better. It's a double hit."

For the study, the researchers asked 541 school children aged between nine and 11 to fill in surveys about how much fish they ate, and then measure their IQ. Their parents were then asked about the quality of sleep.