(CNN) Both the UK National Health Service and the American Academy of Pediatrics recommend that mothers exclusively breastfeed until about 6 months of age and then begin to introduce solid foods.
Yet, an alternative feeding plan is also safe for babies, new research suggests.
Introducing a child to solid baby foods after just 3 months was associated with a small but significant improvement in nighttime sleep and slightly fewer wakings throughout the week compared with babies who began eating solids later, according to a study published Monday in the journal JAMA Pediatrics.
For Dr. Gideon Lack, senior author of the study and a professor and head of the Department of Paediatric Allergy at King's College London, the study's single most important finding was the "more than 50% reduction in the number of families reporting severe sleep disturbances in their babies."
"Lack of sleep can be pretty devastating for babies and their families," he said.
Many parents assume that a belly filled with solid food and not just liquids will help their infants sleep throughout the night, but previous scientific studies have not proved it.
So, while planning a study that examined how allergies develop in babies -- the Enquiring About Tolerance or EAT study -- Lack and his co-authors decided they might also design the study to explore the connection between infant diets and sleep habits.
"Right from the start," said Lack, "we embedded into the structure of the study very detailed, validated questionnaires that assess sleep."
The research team began by recruiting more than 1,300 babies in England and Wales between 2009 and 2012. All the babies were 3 months old, healthy, full-term infants whose mothers exclusively breastfed them.
Next, the researchers sorted the mothers into two groups. One group was asked to exclusively breastfeed the infants till six months, while the second group was asked to continue breastfeeding yet also introduce solid foods for the first week of the study -- the babies were 3 months old -- and in the second week begin to include six items that are typically linked to allergies in children: cow's milk, peanut, hen's egg, sesame, white fish and wheat.
Then, the team collected data on the infants every month up to one year and then every three months up to 3 years old.
The mothers in the first group, on average, introduced solid foods to their babies at 23 weeks of age, whereas the mothers in the second group did so on average at age 16 weeks, the researchers found. Soon after 6 months, then, no real differences existed between the babies with respect to solid foods.
However, the two groups showed differences in sleep, the results indicated.
The babies who ate solid foods earlier slept longer from age 5 months past 1 year: about 7 minutes longer on average each night, with no differences in daytime sleeping.
Lack said that once adjustments were made for factors associated with sleep duration "the sleep difference is more on the order of 16 or 17 minutes a night which correlates to about 2 hours extra sleep a week."
The babies whose diets included solid food earlier also woke less frequently during the night: They averaged about two fewer middle-of-the-night wakings each week than the others.
The parents of babies in the early solid foods group also reported fewer very serious sleep problems than parents in the other group. The definition of a "serious sleep problem" was left to parents, who often perceived difficulties when their babies woke frequently or did not sleep long at night.
These improvements in sleep seen in the early solids group did not end after seven or eight months as the researchers expected but continued throughout the first year of infancy and beyond.
"We were all -- me and my co- investigators -- we were very surprised by this finding," said Lack, who added this sustained difference between groups suggests "that sleep patterns and sleep activities are imprinted or rather developed very early on in life."
Lack also said the analysis didn't "find specific foods associated with better sleep." The mothers in the early solids group fed their children a variety of foods, including vegetables, fruits and rice in addition to the suggested allergenic foods.
Though the large number of families participating in the study may strengthen the findings, one pediatrician has concerns about the study's findings.
"Parenting lore suggests that feeding babies solids can help them sleep better. This study may support that theory, although past studies have not necessarily shown it," said Atlanta pediatrician Dr. Jennifer Shu. "It's possible that feeding more breast milk or formula may have the same effect."
Shu, who was not involved in the research, noted that there are "numerous known benefits of breast milk."
"My concern would be that the recommendation of early introduction of solids (especially when increased very quickly) could result in a corresponding decrease in valuable breast milk consumption," Shu wrote in an email. She added the decision to start solids at a certain time is best decided by the parents and pediatrician based on a baby's growth and general health.
Overall, Shu felt the improvements in infant sleep seen in the study were "small." "Parental quality of life is important but it remains to be seen if introducing solids before 6 months and/or getting small improvements of sleep is the solution," said Shu.
"There are other ways to improve an infant's sleep that are not related to feeding, including having consistent sleep routines and avoiding over-stimulation (such as from artificial light or not giving babies the opportunity to sleep when they need it)," said Shu.
Lack said that, going forward, more research is needed to examine "not only quantity of sleep but also quality of sleep in babies."
"Prolonged breast feeding is extremely important," said Lack. "The study highlights the fact that it is safe and potentially beneficial to introduce solid foods, including allergenic foods, into a baby's diet after 3 months of age."