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Posts tagged ‘Allergies’

Breast may be best, but why isn’t it better?

In honor of World Breastfeeding Week (yes, yes, I know–it ended yesterday), we need to talk about a widely overlooked aspect of breastfeeding, its recipients!

Nope, I am not talking about our babies. (After all, who could overlook them?) I am talking about their gut bacteria.

Breast milk contains special carbohydrates (called HMOs for Human Milk Oligosaccharides) designed to nourish specific gut bacteria, especially a type known as Bifidobacteria. Bifidobacteria contain genes desiged to metabolize HMOs–implying they have co-evolved with us for a long time.

This process of seeding your baby’s gut begins not with breastfeeding, though, but before birth. During pregnancy, women’s bodies cultivate these bacteria while pruning out others, seemingly in preparation to pass them onto our babies during birth.

Why does this matter? Health benefits.

Breastfeeding may benefit health indirectly–by cultivating the right gut bacteria. Scientists now believe that having the right balance of gut bacteria helps to calibrate your baby’s immune system and metabolism, possibly with lifelong effects.

I dig into the latest research on this breastfeeding-gut-health axis in my latest post for BloomLife. Check it out!

https://preg-u.bloomlife.com/breast-may-be-best-but-why-isn…

No, C-sections Are Not “Best With a Little Labor”

Children born by C-sections have about 20% higher odds of obesity, asthma, allergies, and Type 1 Diabetes, according several large research reviews.

But are children born by scheduled C-sections especially at risk for health problems, as a recent New York Times piece claims?

“the data showed more health problems among babies born by planned C-section than among those delivered by emergency C-section or vaginal birth, even though the planned surgery is done under more controlled conditions. The finding suggests that the arduous experience of labor — that exhausting, sweaty, utterly unpredictable yet often strangely exhilarating process — may give children a healthy start, even when it’s interrupted by a surgical birth.”

A reader, confused by this New York Times piece, wrote to ask for my take. “Are planned C-sections really less safe?” she asked. “The actual study… didn’t seem to support what the NYTimes article claimed.”

And after reviewing the research myself, I have to agree.

The study in question, led by Dr. Mairead Black of the University of Aberdeen, and one of the largest and best-designed studies on long-term health following delivery by C-section, actually did not find more health problems among children born by planned C-sections than those born by emergency C-sections.

(The sole exception was an unexpected–and probably artifactual–increase in Type 1 Diabetes; more on this in a moment).

How Does This Study Fit in With What We Already Know?

Although C-sections have been consistently linked with poorer long-term health in children, scientists are still not sure why.

One possibility is babies miss out on the “sweaty and exhausting” experience of labor. The physical trauma of birth kickstarts the baby’s internal stress response, pumping cortisol through their veins, and giving their organs, including the lungs, the final push to full maturity.

Another possibility, favored by many scientists, is that C-sections alter the baby’s gut microbiome. C-section  babies miss out on the messy, bacteria-laden, splash into every bodily fluid passage through the birth canal–the route by which nature normally seeds a baby’s gut microbiome.

“If a baby is born naturally, it comes into contact with bacteria from the mother, which might help with immune system development,” lead researcher Dr. Mairead Black told The New York Times.

Compared to babies born by C-section, babies born vaginally have a more diverse and healthy gut microbiome–believed to be critical for their development of a healthy, balanced immune system (one good at attacking pathogens, but not overly jumpy and prone to self-attack).

Or perhaps the issue is not C-section birth per se, but the hodgepodge of pregnancy and birth complications that often result in C-sections, such as stalled labor, intrauterine growth restriction, and preterm birth.

To study one piece of this puzzle, the importance of labor-induced fetal stress, Black and colleagues at the University of Aberdeen in the UK compared babies born by planned versus emergency C-sections. Babies born by planned C-sections experience no labor, while babies born by emergency C-section often experience some, even though it is cut short.

Black and colleagues followed over 300,000 full-term singleton babies born to first-time mothers in Scotland between the years 1993 and 2007. Roughly 4% were born by planned C-sections, and 17% by emergency C-sections.

Compared to children born by emergency C-sections, babies born by emergency C-sections were at no higher risk of virtually every health outcome Black and colleagues assessed–asthma, inflammatory bowel disease, obesity at age 5, cancer, or all-cause mortality. In fact, these children born by planned C-section had a wee bit lower risk of dying during their first year of life.

The one exception: Children born by planned C-section appeared to have 50% higher risk of developing Type 1 Diabetes. (A 50% higher risk sounds scary, but because Type 1 Diabetes is rare, this amounts to only 2 additional diagnoses for every 1000 children.)

As the researchers acknowledge, the apparent increase in Type 1 Diabetes was probably not caused by birth by planned C-section, but by some artifact of their study’s design, a third factor not adequately accounted for in their research.

Why did they think this effect was not real? Because children born by planned C-section were not at higher risk of Type 1 Diabetes compared to children born vaginally, a pattern of results inconsistent with prior research, and one which makes little sense. If anything, the researchers expected the opposite, planned C-sections would lower the risk of Type 1 Diabetes. Earlier research has found severe fetal distress stress during labor–something obviously more common during emergency C-sections than during planned ones–raises the risk of Type 1 Diabetes.

My guess? The researchers were unable to completely account for maternal Type 1 Diabetes. Having a mother with Type 1 boosts a child’s chances of Type 1 Diabetes by about 10-fold. (Black and colleagues did try to control statistically for maternal Type 1 Diabetes, but were missing this information for some of the mothers.) To avoid complications during labor, many women with Type 1 Diabetes deliver by planned C-section.

C-sections Versus Vaginal Births

How did the children born by C-section fare compare to those born vaginally?

Overall, children born by C-section, planned or emergency, were more likely to be hospitalized for asthma and had higher mortality rates during the first year of life as well as throughout childhood.

Contrary to earlier research, though, children born by C-section were no more likely to develop inflammatory bowel disease, Type 1 Diabetes, obesity, or cancer.

The Bottom Line

The NYT headline is misleading: Planned C-sections do not lead to worse health outcomes than emergency ones.

The one exception: children born via planned C-sections had a 50% higher risk of Type 1 Diabetes, but only compared with unplanned C-sections. No difference was seen when comparing children born by planned C-section with those born vaginally, a pattern of results which, as the researchers themselves acknowledge, does not make any sense. In fact, this pattern runs counter to prior research, which suggests severe fetal distress during labor ups the odds of Type 1 Diabetes, and a recent meta-analysis which found that C-sections of all types up the odds of Type 1 Diabetes by about 20%.

Why is birth by C-section associated with poorer health? We still do not know. Given the impossibility of randomized controlled trials for childbirth, we may never know.

But this study does have one take-away: missing out on labor-driven stress response is probably not the critical issue. If it were, we would see significantly worse health outcomes among children of planned C-sections than emergency C-sections.

As for the risks of C-sections overall, that’s too big of a topic for me to tackle here. But I will say this: C-section-driven health risks are minor. They are almost certainly swamped out by who we are–the genetic blessings and curses we bestow on our offspring–and what we do as parents.

(Not reassured? You can always swab your C-section-born baby’s skin and mouth with your vaginal secretions, as widely-respected gut microbiome researcher Rob Knight did after his wife’s emergency C-section. I certainly would.)

 

Questioning Breastfeeding’s Benefits Does Not Make Me Anti-Breastfeeding

Earlier this week, I wrote about the alleged benefits of breastfeeding being vastly overstated.

My goal in writing that post was not to nurse some long-standing grudge against breastfeeding advocates. Nor was it an attempt to justify my own parenting choices: I breastfed both my children for well over a year.

(And yes, as some readers have inquired, I know just how wonderful breastfeeding can be. How breastfeeding your baby can be calming and joyful, even magical. But whether I found breastfeeding magical or a chore–or, in actuality, both–has nothing to do with whether it lowers the risk of asthma, or heart disease, or anything else.)

In response to my post, someone shared this comment on Facebook:

“Anyone who thinks this [my post] a solid piece of work needs to read my latest book, Milk Matters: infant feeding and immune disorder. No one has to prove that breastfeeding (the evolutionary and physiological norm that provides free stem cell transplants) makes a positive difference. Those who assume, claim or promote artificial feeding as safe or adequate need to prove that deviating from such basic physiological norms is safe, that there are no short or long term harms from doing so. …”

I am sharing this comment not because I find it particularly compelling, but because I think it nicely illustrates the problem with arguments made by many breastfeeding advocates: They start with the assumption that breast is best. And then, inevitably, they fail to scrutinize the evidence, no matter how flimsy, that supports that assumption.

And the evidence is flimsy indeed. Most of the alleged benefits of breastfeeding are found only in observational studies, which are widely acknowledged as biased. On average, breastfeeding mothers have a higher levels of education, higher incomes, and live in safer neighborhoods than formula-feeding mothers, granting their children an early leg up in life. Separating the effects of breastfeeding from these other advantages is next to impossible.

How do we know that these observational studies are biased? Primarily because we do not find the same benefits in better-designed studies–sibling comparison studies and the PROBIT randomized controlled trial. The only clear-cut benefit seen in these studies is a lower risk of severe vomiting and diarrhea during infancy. (For a detailed summary, see my earlier post).

To be fair, breastfeeding advocates are right, in a way. Breastmilk does contains numerous hormonal, antimicrobial, immunological, and nutritional factors not found in formula. This is why breastmilk helps protect against vomiting and diarrhea during infancy.

Before the advent of clean water, sanitation, and modern medicine, breastfeeding was frequently life-saving. In countries where access to these resources remains limited, it still is. There’s no bigger possible benefit than survival.

But these beneficial properties do not imply that breastmilk has any long-term benefits for the panoply of modern ailments: allergies, asthma, obesity, type 2 diabetes, and cardiovascular disease. We cannot claim such long-term benefits without sound empirical evidence. And that is entirely lacking.

If the American Academy of Pediatrics, and others were to say, “We recommend breastfeeding because it reduces the risk of severe diarrhea and vomiting during infancy, and because breastmilk contains unique immune, hormonal, and nutritional factors not found in formula, the long-term benefits of which are unknown,” I would have no problem with their claims.

But instead, they have chosen to present poor quality evidence as fact. Playing fast and loose with the evidence in this way undermines their credibility. Worse, it violates the trust that women have placed in them.

Breastfeeding Benefits: The Real, the Imagined, and the Exaggerated

Breastfeeding lowers your child's risk of obesity, asthma, and allergies. Or does it? The best available research implies these claims are vastly overstated.

Read more

The NEJM Peanut Study: Is It Better to Introduce Allergenic Foods Early?

In 2000, the AAP advised delaying introduction of peanuts and tree nuts until age 3. But new research finds delaying exposure considerably boosts the chances of a peanut allergy.

Read more

Introducing Solids: Is It Best to Wait Until 6 Months?

In 2005, the American Academy of Pediatrics (AAP) changed their recommendations from gradually introducing solids between 4 and 6 months of age to exclusively breastfeeding for “about the first 6 months of life. For the first 6 months “your baby”, they assert, “needs no additional foods (except Vitamin D) or fluids unless medically indicated.”

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My daughter at 9 months, eating peas and Cheerios

You might think that these recommendations were updated because of a new evidence showing substantial benefits for the baby of delaying the introduction of solids.

But, nope, this is not the case. Instead, these changes were motivated by studies showing an absence of harm to the baby and some minor potential benefits for the mother.

The World Health Organization was the first major medical organizations to recommend exclusive breastfeeding for 6 months, for reasons they outline in a 2002 research review (updated in 2007):

  1. No evidence exclusive breastfeeding for 6 months results in poor growth
  2. No apparent increase in the risk of allergies*
  3. A longer period of lactation-induced infertility, about an extra month on average
  4. Greater postpartum weight loss between 4-6 months, about a pound on average
  5. Lower risk of illness for the first six months, and possibly throughout the first year

* (Since this review was published, new evidence suggests delaying solids until 6 months may increase the risk of food allergies. More on this complex topic below.)

When weighing the pros and cons of exclusive breastfeeding for 6 months, the social and environmental context matters. The WHO crafted its guidelines to maximize health outcomes in both developing and developed nations. But benefits that have a large public health impact in the developing world, where access to basic medical care, birth control, clean water, and nutritious food is limited and inconsistent, can have little or no impact in the developed world.

Benefits of Exclusive Breastfeeding for Six Months

For mothers living in the developed world, the benefits of exclusive breastfeeding for 6 months are small, arguably negligible.

We have been blessed with access to birth control, so lactation-induced infertility is not a critical means of pregnancy prevention and birth spacing.

And, when it comes to weight loss, although almost every mother I know would gladly shed an extra pound or 2 of baby weight, the benefit is really small, just an extra a pound on average. Surely there are other activities that do not require 8-hours a day, round-the-clock efforts that would be just as effective forms of weight loss.

Certainly neither of these two benefits warrant the stress placed on introducing solids “at the right time.”

Of the reasons given by the WHO, the only truly persuasive one is a reduced risk of illness for the baby during its first 6 to 12 months of life. Here again, though, there are important differences between the developing and the developed world.

In the developing world, exclusive breastfeeding for 6 months is literally life saving. Within the 42 nations with the highest child mortality rates, widespread adoption of exclusive breastfeeding for 6 months would prevent an estimated 13% of the deaths of children under the age of 5. This is a larger percentage than would be saved with improved access to antimalarial medication or antibiotics.

Within the developed world, the picture is more nuanced. Here, completely weaning from breast milk before 6 months, or introducing solids before 4 months, or introducing formula before 6 months substantially increases the risk ear infections, diarrhea, pneumonia, and bronchitis.

But gradually introducing solids between 4 to 6 months while continuing to breastfeed does not. Studies that compare the outcomes of infants who were exclusively breastfed until 6 months (EBF or exclusively breastfed) with those who were exclusively breastfed for at least 4 months and then partially breastfed thereafter (MBF or mostly breastfed) find that 6 months of exclusive breastfeeding neither harms nor benefits growth and development.

The only apparent benefit of delaying until 6 months was a 25-50% lower risk of diarrhea in the first year of life. The effects on ear infections, pneumonia, and bronchitis were unclear: A couple of observational studies found a lower risk, but the majority of studies, including the only two randomized controlled trials, found no effect. And longitudinal study conducted in Belarus found no differences in weight, height, BMI, asthma, allergies, or other illnesses by age 6.

“Exclusive breastfeeding for six months does not seem to confer any long-term (at least to early school age) protection against obesity or allergic disease, nor any benefits in cognitive ability or behaviour, compared with exclusive breastfeeding for three to four months with continued partial breastfeeding to six months.”  – Kramer & Kakuma, 2012

Costs of Exclusive Breastfeeding

Lower Iron Status. EBF infants tend to have lower iron levels than mixed fed or formula-fed infants. Two randomized controlled trials, one conducted in Honduras and the other in Iceland, found significantly higher iron levels among MBF than EBF infants. Reassuringly, at 6 months of age, iron levels in both groups remained within the normal range, and the EBF infants were not more likely to be iron deficient or to develop anemia.

Still, iron needs rise sharply in the second half of the first year when newborn iron stores have been depleted, and lower iron status in the first six months could place EBF babies at higher risk of iron deficiency as they age. This is why the CDC considers “breastfed babies who after age 6 months are not being given plain, iron-fortified cereals or another good source of iron from other foods” to be at high risk for iron deficiency and anemia.

Increased Risk of Food Allergies. On this point, the advice given to parents has seesawed from it is best to delay solid foods, especially highly allergenic ones, to it is best to introduce these foods early, between 4 to 6 months. This is because the evidence behind the advice is of poor quality and inconsistent. A handful of observational studies find that early introduction increases the risk of allergies. A comparable number find that late introduction increases the risk. And not all of the studies find when solids are introduced matters at all.

Some researchers to speculate that there is something of a sweet spot in infancy, between 4-6 months of age, when introducing solids lowers the risk of allergies. This protective effect may be strongest for peanuts and cooked whole eggs. But until proper clinical trials have been done, it seems wise not to make too much of these findings. (UPDATE: A randomized controlled trial has now shown that introducing peanuts before 1 year of age lowers the risk of a peanut allergy substantially. More on this study here.)

The AAP no longer recommends waiting to introduce solids until 6 months or later to reduce the risk of allergies, and instead advises waiting until at least 4 months. And of course, this statement on solids and food allergies conflicts with guidance the AAP gives elsewhere to exclusively breastfeed for 6 months.

Conclusions

Like so many parenting decisions, the actual evidence suggests that we can all relax a bit. For those of us lucky enough to live in the developed world, introducing a small amount of solids between 4 to 6 months is unlikely to harm our babies, and equally unlikely to benefit them.

That said, when giving your baby solids before 6 months, it makes sense to provide small amounts. The immune benefits of breast milk are dose-dependent: the more milk the baby takes in, the greater the protection from illness. This is why solids during the first year should not be used to replace but to supplement breastfeeding. And when introducing solids, especially to exclusively breastfed babies, it makes sense to emphasize iron rich foods like broccoli, meat, eggs, fish, and fortified cereals.

Here is most sensible statement I found on the 6-month rule, from a review article in The BMJ, the flagship journal of the British Medical Association:

“From a biological perspective, the point when breast milk ceases to be an adequate sole source of nutrition would not be expected to be fixed, but to vary according to the infant’s size, activity, growth rate, and sex, and the quality and volume of the breast milk supply.”  – Fewtrell, Booth, & Lucas, 2010

When did you first introduce solids? Did the risk of allergies or infections play a role in your decision?

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