The study showed that infants in the group who ate solids as well as breast milk slept longer, woke less frequently and had far fewer serious sleep problems than those who were exclusively breastfed until about six months.
One group was exclusively breastfed for six months, the other group was given solid foods in addition to breast milk from the age of three months.
Parents completed online questionnaires every three months until their baby was a year old and then every three months until their child was three years old.
Parents' perceptions of a sleep problem with their child were correlated with maternal and global sleep quality of life, and perception of infant sleep problems correlated with nighttime sleep duration and night waking frequency, the authors wrote.More news: Steven Gerrard says England will beat Croatia and are a 'dangerous' team
All the babies were breastfed, but about half started getting certain solid foods in addition to breast milk from age 3 months or somewhat later, but before they were 6 months old.
Babies given solid food earlier on in life sleep better, according to a new study.
One finding deemed crucial by Lack was that the parents who exclusively breastfed for those first six months were twice as likely to report an issue with their child's sleep than those in the solids group.
The researchers from King's College, London, and the University of London admitted it was possible that mothers giving their babies solids may have responded to their questions in a more positive manner, having expected a positive effect, since many parents already believe that the practice encourages better sleep.
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However, most mothers in Britain already ignore this advice, with 75 per cent introducing solids before five months and 26 per cent saying they did so to stop their babies becoming hungry overnight.
Dr Clare Llewellyn and Dr Hayley Syrad, who have researched baby eating habits for over a decade, said the first foods introduced to children at around six months should be bitter vegetables, as these are the foods most commonly disliked by children.
The NHS Choices website says: "Starting solid food won't make your baby any more likely to sleep through the night".
"There is no clear physiological reason why introducing solids foods early would help a baby sleep, especially not for the very small amounts parents were instructed to give in this trial", she said.
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