Bottle-Feeding & Asthma Risk
Every week or so I take a deep dive on Google Scholar to see what interesting studies I can find. This provides an excellent opportunity to learn things about breastfeeding that I wouldn’t have thought to study on my own. It also is a great place to find exciting things to talk about on the blog!
I stumbled upon this study written in late 2017 that looked at the risk of childhood asthma and feeding method. I think it’s pretty common knowledge by now that WHAT we feed our babies has a long-term health impact, but according to this study, so does HOW we feed them. It’s oft thought that breastfeeding provides protection against these illnesses and diseases that seem to affect bottle fed/formula fed babies at increased rates, and that’s not an incorrect thought at all.
But assuming that direct breastfeeding is the biological norm, I wanted to see if I could find a scientific answer as to why bottle-fed babies have an increased risk of childhood asthma. Turns out the literature on the correlation between bottle feeding and childhood asthma and other respiratory issues is vast!
Let’s take a look at a few compelling studies!
Bottle Feeding in the Bed or Crib Before Sleep Time and Wheezing in Early Childhood- 2002
In a study of 448 children whose parent had a history of having a genetic tendency to develop allergic diseases since birth, researchers found that the risk of having recurrent wheezing and asthma between 1 and 5 years of age was higher with every bottle they received in bed before sleep during their first year of life.
This study didn't specify if they controlled for cows milk or human milk, so it's impossible to say that the bottle feeding alone caused the increased risk.
Prolonged bedtime bottle feeding and respiratory symptoms in infants-2012
Another study that focused on night time bottle feeding found that prolonged bedtime bottle feeding might be one of the causes of chronic respiratory symptoms in infants. Their sample size was 44 infants whose mean age was 15.8 ± 7.8 months (age range, 6-39 months). The conclusion in this study echoed the findings of the previous research that early discontinuation of bottle use leads to fewer instances of respiratory issues.
Feeding Bottles Usage and the Prevalence of Childhood Allergy and Asthma-2012
As mentioned in the study, "This study aimed to examine the association between the length of use of feeding bottles or pacifiers during childhood and the prevalence of respiratory and allergic morbidities." Researchers analyzed a total of 14,862 questionnaires performed in day care centers and kindergartens and compiled the data to find trends in the affects bottle feeding had on health issues such as asthma, wheezing, and eczema.
Again, the findings of this research support the claims that more extended bottle feeding is associated with an increased risk of asthma.
At this point, all the of the studies I have posted reinforce the same idea, that bottle feeding is a risk factor for asthma. What they do not do, however, is address the question of "do babies receiving only bottled breastmilk have an increased risk of asthma and wheezing?" Which brings me to why the latest study is so amazing.
Modes of Infant Feeding and the Risk of Childhood Asthma: A Prospective Birth Cohort Study.- 2017
They conclude: "Modes of infant feeding are associated with asthma development. Direct breastfeeding is most protective compared with formula feeding; indirect breast milk confers intermediate protection. Policies that facilitate and promote direct breastfeeding could have an impact on the primary prevention of asthma."
Which means, babies who are breastmilk fed via bottle still have an increased risk of asthma in childhood, though not as high as those who are exclusively formula fed.
Why might bottle feeding cause Asthma?
The exact reasons are not crystal clear, but there are some well-accepted theories.
1) Immaturity of the suck/ swallow /breath reflexes causes disorganization, especially in a supine (laying on the back) position, which allows for Gastroesophageal reflux (GER) and micro-aspiration. The liquid entering the airways from the micro-aspiration can cause irritation that has long-term effects.
Additionally, bottles by design, are more difficult for babies to control the flow and so even those who have robust suck/swallow/breath coordination may still be challenged by the bottle. Breastmilk is shown to be less harmful during micro-aspiration than formula, but the most recent study may indicate that it's something that needs to be considered more in-depth.
2) Concerning nighttime bottle use, the key to increased asthma risk might be due to the control of the autonomic nervous system. The autonomic nervous system is decreased during sleep, and it's not uncommon for adults even, to microaspirate on small amounts of saliva. In infants, the rate of contraction or squeezing in the pharynx is reduced during sleep, resulting in a decrease of swallowing of the oropharyngeal secretion and increased GER and microaspiration. Again, microaspiration being a bad thing.
So why is this important?
Many parents choose to bottle feed expressed breastmilk or formula in attempts to get their babies to sleep longer. Even though there is a ton of information showing that frequent night waking to nurse is biologically normal and protective against SIDS and that formula fed babies don't sleep more hours total compared to breastfed babies, it can be tempting in a sleepy haze to want to feed baby into slumber.
Night time feeding especially seems to have a unique set of risks that may provide an additional deterrent against the "bottle for bed" practice.
For many families bottle use is a necessary part of their daily routine and it's near impossible to time feeds in a way to avoid post feed sleeps. I hope, however, that this post may provide additional information to those who are leaning towards bottle use in hopes of getting their babies to sleep longer, so that you if you continue to do so, you at least do it with more knowledge in your pocket. :)