But the new study suggests that advice is flawed - and suggests babies do better if solid food is given earlier, alongside breastmilk.
The study showed that infants in the group who ate solids as well as breast milkslept longer, woke less frequently and had far fewer serious sleep problems than those who were exclusively breastfed until about six months. The second group, while continuing to breastfeed, were asked to introduce solid foods to their infants' diet from the age of three months.
Mary Fewtrell, the nutrition lead at the Royal College of Paediatrics and Child Health, says that their group is now recommending mothers to wait until 6 months before starting to feed their children solids. The difference peaked at six months of age, with the early introduction group sleeping an average of almost 17 minutes longer, and persisted after the infants' first birthday.
They also woke less frequently.
"Given that infant sleep directly affects parental quality of life, even a small improvement can have important benefits", Perkin explains to BBC.
Specifically, their no-schedule sleeping schedule in a baby's life can leave mothers and fathers just as exhausted, cranky, and sleep-deprived as their newborn child.
Professor Mary Fewtrell of the Royal College of Paediatrics and Child Health said: 'These are interesting findings from a large randomised controlled trial. "This is quite a well-designed study to actually answer that particular question", he said.
The Government now advises mothers to feed babies exclusively with breastmilk until they are at least six months, and only then gradually introduce solids.
When an infant's frequent nighttime wakeups are causing concern and anxiety, parents can consult their paediatrician about whether starting solid food would be appropriate, Dr Kim said. "Generations of pediatricians on both sides of the Atlantic have encouraged parents to delay the introduction of solid foods, [in part] based on expert opinion which said that this would limit food allergy". She suggests maintaining a safe sleep space for baby by using a co-sleeper (which attaches to the parents' bed) so that it's easier for moms to get back to sleep after nursing.
In addition to decades of research finding breast milk to be nutritionally complete, breastfeeding also has been linked to stronger immunity, healthy brain development, lower obesity risk, reduced Sudden Infant Death Syndrome rates, higher educational achievement and also various maternal health benefits. "It's nice to have studies like this to carve out actual data to help manage this problem".
"There's a bit of polarization around this issue", he said.