Formula recommendations may be tainted by financial interests, says the study.
Allergic and autoimmune diseases are leading causes of chronic illness among young people, and their prevalence is on the rise.
There is evidence that consuming intact cow's milk protein in the form of infant formula in early life may increase the risk of these diseases.
To reduce the risk, current infant feeding guidelines in North America, Australasia and Europe recommend giving infants hydrolyzed cow's milk formula instead of standard infant formula.
The US Food and Drug Administration (FDA) and a Cochrane systematic review have supported this approach.
"Hydrolyzing," or treating the product with heat to break down the milk proteins, has been claimed to help prevent allergy or autoimmune diseases, especially among those with a family history.
Robert Boyle, of Imperial College London in the UK, and colleagues carried out a systematic review of the benefits of different types of milk. To do this, they undertook a meta-analysis of 37 trials between 1946-2015.
The studies included over 19,000 participants and compared data about hydrolyzed cow's milk formula with another hydrolyzed formula, human breast milk and a standard cow's milk formula.
Formula offers no additional protection
The trials reported on allergic diseases, autoimmune conditions and any allergic sensitization outcomes. Common conditions included asthma, eczema, allergic rhinitis, conjunctivitis, food allergy and allergic sensitization, and type 1 diabetes, which is an autoimmune disease.
Contrary to recommendations made in current international guidelines, the results indicate that partially or extensively hydrolyzed formulas offer no additional protection, compared with other options.
Nor was there any evidence that a partially hydrolyzed formula could reduce the risk of eczema, a claim supported by the FDA, or that hydrolyzed formula could prevent cow's milk allergy, as cited by a Cochrane review.
Fast facts about formula feeding
- 1 million infants in the US consume formula milk from birth
- 2.7 million are consuming at least some formula milk by the age of 3 months
- Guidelines recommend formula fortified with around 12 mg of iron.
The authors call for a review of current infant feeding guidelines, due to the lack of consistent evidence supporting them.
All the studies and evidence were assessed for quality.
Concerns were raised about the low quality of some evidence, with indications of conflicts of interest emerging, particularly where there were financial links with baby formula manufacturers. Potential bias related particularly to allergic outcomes, eczema and wheeze.
In a linked editorial, Caroline Lodge and colleagues from the University of Melbourne in Australia expect that experts will recognize the lack of evidence supporting the ability of hydrolized formula to prevent allergies.
Even so, they may continue to recommend the formulas, because there is a chance they might prevent allergic disease, and, in any case, they are unlikely to cause any harm.
However, this approach can lead to an undermining of efforts to promote breastfeeding, which is the optimum mode of feeding for infants.
Not questioning the guidelines can also deter attempts to conduct more definitive research and hinder efforts by formula producers to improve products.
Lodge and co-authors conclude:
"It is now time for this evidence to be used for updating and clarifying current recommendations and guidelines. Furthermore, we encourage industry to pursue development of effective allergy-reducing infant formulas and call for further transparent and well-conducted studies in this area."
Medical News Today recently reported that probiotic formula may increase tolerance to cow's milk.