How, when and where a child is born may all play a role in lifetime asthma risk, new studies suggest.
Asthma occurs when airways in the lungs spasm and swell, restricting the supply of oxygen. The incidence of asthma in the United States has risen steadily for more than two decades, and now affects about 6 percent of children, up from less than 4 percent in 1980, according to the Centers for Disease Control and Prevention.
The reasons for the increase are not entirely clear. Genetics probably plays a role in risk for asthma, but an array of environmental factors — pollen, dust, animal dander, mold, cockroach feces, cigarettes, air pollution, viruses and cold air — have all been implicated in its development.
This month, The American Journal of Respiratory and Critical Care Medicine is reporting that children born in the fall have a 30 percent higher risk for asthma than those born in other seasons. The finding is based on a review of birth and medical records of more than 95,000 children in Tennessee.
A possible explanation is that autumn babies tend to be about 4 months old at the peak of cold and flu season. By that age, many babies are in day care, regularly exposed to the outside world.
And while their lungs are still developing, they have lost immunities conferred in the womb and have yet to develop their own strong immune systems. As a result, fall babies are at particular risk to contract a severe winter virus, which may in turn increase their risk for asthma.
The lead researcher, Dr. Tina V. Hartert, director of the Center for Asthma Research and Environmental Health at Vanderbilt University, says some parents with a high familial risk for asthma may want to consider timing conception to avoid a fall birth.
But since that is impractical for many people, Dr. Hartert says all parents should take precautions to reduce a baby’s risk of a respiratory infection.
“It’s premature to say you should time conception so children aren’t born in the fall,” she said. “But it’s good sense to use typical hygienic measures to try and prevent illness.”
As for how a baby is born, Swiss researchers are reporting in the journal Thorax this month that a Caesarean delivery is linked to a much higher risk for asthmacompared with babies born vaginally.
In a study of nearly 3,000 children, the researchers found that 12 percent had been given a diagnosis of asthma by age 8. In that group, those born by C-section were nearly 80 percent more likely than the others to develop asthma. The explanation may be that a vaginal birth “primes” a baby’s immune system by exposing it to various bacteria as it moves through the birth canal.
Finally, researchers at Tufts reported last month in The Journal of Asthma that a baby’s place of birth also influences asthma risk. In a study of black families in Dorchester, Mass., they found that babies born in the United States were more likely to have asthma than black children born outside the country.
The reason for the disparity isn’t clear, but the sterile conditions under which American babies are born may be a factor. Babies in developing countries encounter more infections, so they may be better equipped to withstand less serious assaults associated with asthma,like mold and dust mites.
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From 1 to 25 of 59 Comments
The seasonal variation likely has to do with pollens and allergies.
However, one of the best kept secrets in the profession is medicine is that asthma is strongly related to dietary factors - allergies to cow’s milk protein being one of the most common allergens, but there are others. That would also certainly explain the decreased incidence of asthma in certain other countries. The per capita dairy intake in children over the last few decades is much higher than it was about a century ago.
I have been a primary care physician in Internal Medicine for over 20 years and have seen scores of asthmatic patients who have taken advice of dietary manipulation, especially reducing cow’s milk products intake, and have benefited significantly with a reduction in the asthma attacks, and in some cases even a cure.
I tell my asthmatic patients who are interested in trying, to eliminate dairy first for about 2 weeks totally, and see if there is an improvement. A high percentage of asthmatics will notice an improvement, often dramatic.
Robert Baker
— Robert Baker, MDrcbaker200@comcast.net
C-sections tend to run the gamut though. There are those that are planned, where I’m guessing the baby doesn’t really even enter the cervix, and is delivered from the uterus itself. Then there are those that are unplanned, where the baby is usually halfway down and is not progressing, and a C-section is ordered. What about those cases? I’m just curious.
Yes, while babies born outside the country are generally I think less at risk for asthma, some do end up with allergies that may not manifest with asthma after moving here. I think though, in those cases, it’s a question of genetic predisposition to allergies rather than environment of birth. It’s all very interesting stuff though.
http://sospokesaroj.wordpress.com
— SarojFrom this article I cannot find a conclusive result. My frank opinion is that a lot of asthma babies and children are the result of mothers smoking during their pregnancy.
FROM TPP — Hmmm…obviously smoking is a risk but that certainly can’t explain the epidemic.
— Onno Frowein“a vaginal birth “primes” a baby’s immune system by exposing it to various bacteria as it moves through the birth canal.”
Then why not scrape some of that there beneficial bacteria from the birth canal and lather it on the newly C-sectioned baby?
— Susanna“Then why not scrape some of that there beneficial bacteria from the birth canal and lather it on the newly C-sectioned baby? –Susanna”
Susanna, have you any idea how long it is going to take for me to talk my uterus back down out of my thorax?
— ErinHere is another possibility.
We already know that kids living near major roads have greater risks of asthma. Diesel emissions appear to be somewhat more important that gasoline, although that isn’t definitive.
So what might that have to do with fall birth?
Some diesel emissions are “semi-volatile,” meaning they are gases when it is hot and tiny particles when it is cold, in the winter. It sounds far fetched, but perhaps the emissions in particle form lodge more easily in the lungs of developing tots. Just a hypothesis…
— JohnI wonder how useful this type of information really is? Firstly, even if the statistical association is there, the explanation that is offered is really the researchers’ guess. Secondly, telling somebody not to give birth in fall is nice.. but for so many people not really practical. Often we don’t conceive on demand. Plus, c-sections are also not exactly our choice (women who can successfully give birth vaginally, but choose c-sections are an absolute minority). I also wonder how much a c-section by itself, minus all other compounding factors, really matters. A baby doesn’t spend much time in the birth canal anyway. I do strongly believe in the “germ” theory of allergies - that not being exposed to germs and pollutants and sterilizing everything is detrimental. Research shows that kids who grow up on farms have a lot less allergies. My advice to people who try to prevent allergies in their kids is stop sterilizing everything, and, if possible, get a dog or a cat. Besides being great companions, pets help your kid avoid allergies.
— IMKOne more thought:
How much has the rate of C sections increased in the last two decades?
How does that rate compare to the rate of increase in asthma incidence?
The CDC reports that C section births increased by 46% from 1996 through 2005, to a rate of 30.6% of all births, but this is just for teenagers:
http://www.cdc.gov/media/pressrel/r061121.htm?s_cid=mediarel_r061121_x
This rate of increase is similar to the rate of increase in asthma. However, as most of us know, correlation isn’t causation, we have to understand the mix of different possible causes of the increase in asthma rates. Further, C sections, even if implicated in the increase in asthma generally, wouldn’t explain the issue of fall births.
I haven’t been able to find similar stats, in a fairly cursory search, for increases in C sections for all births (vs. just births to teenagers).
— JohnBefore excluding astrological causes, there should be proof
— fosforosthat the higher percentage of “Scorpio” asthmatics is restricted to cold climates. If the suggested cause is valid, there should be no birthdate differential among Cuban or Jamaican children.
Interesting that Breast Feeding was not even mentioned or the anti-bodies that are passed on to the infant from breast milk that protect the infant from many infections (even within hours of the mother being exposed to them). Many women that opt for C-section do not breast feed. This is a major error in this article to miss the benefits of breast feeding.
FROM TPP– Well, that would be a different study, wouldn’t it?
— KristinWe cannot overlook the dual pandemics of vitamin D and omega-3 fatty acid deficiencies in mothers and their children. These are well-described, relatively new phenomenon with immense implications for the health of both mothers and their children.
Whenever season is raised as an issue, vitamin D status must be considered.
Both D and omega-3’s are crucial in immune competence, TH1 and TH2 balance and in the important anti-inflammatory counter-responses to necessary pro-inflammatory actions.
No pregnant mother should go through her entire pregnancy deficient in either D or omega-3’s. No newborn should grow up deficient in either. Prenatal vitamins, breastfeeding and bottle feeding do not provide enough of these to overcome existing deficiencies. At best they can maintain the level of deficiency. They cannot replenish already low levels.
Bodnar and colleagues (2007) at the University of Pittsburgh have documented that the majority of women at the time of delivery are vitamin D deficient. Yubas and colleagues (2006) have documented that American women have the lowest omega-3 fatty acid content in their breast milk of any population on earth. (Just 1/6th that of Japanese women.)
Until we as a nation prioritize testing low-cost, low-toxicity interventions for prevention and wellness, we will continue to overspend, overtreat, and, increasingly, push families and states towards bankruptcy.
Gregory A. Plotnikoff, MD, MTS
— Gregory Plotnikoff, MDPenny George Institute for Health and Healing
Minneapolis, MN
Interesting! The factors you mention, like peak winter virus exposure and environmental factors related to developing the immune system, do make sense.
But the seasonal timing makes me wonder if vitamin D deficiency is a factor here as well. Studies suggest that vitamin D deficiency, of both mother and child, might be playing a role in the asthma epidemic. A child born in fall might have two vitamin D related seasonal disadvantages:
First, the baby would have been conceived in the winter, and so the crucial first months of fetal development would have taken place when people at most latitudes in the U.S. can’t produce cutaneous vitamin D, and the body’s saved stores from the summer and fall would be diminished.
Second, a fall-born baby and its breastfeeding mother would be spending some of the first months of the baby’s life in winter again. Factor in the likelihood that the first month post-birth would involve less time outdoors, and the fall would be the beginning of the period where, especially at northern latitudes in this country, we can’t produce D from the sun in winter. That study you cited about location looked at people in Boston — another study showed that people in Boston can’t produce D between November and February.
Debs
— DebsFood Is Love/Seattle Local Food
These articles about allergies and asthma reveal the extent that researchers are just guessing. In the part about the seasonal birth, it says that exposure to germs in daycare causes asthma. In the latter part of the full article, it says that babies born in the US and by c-section are at higher risk for asthma and allergies because they are NOT exposed to germs.
— CherylThank you for this information. As a life-long asthmatic (my attacks have sent me for emergency treatment), I was happy to pass along the article to my mother.
I think the recent reserach on asthma shows that we have many theories but we don’t really know what casues asthma or why it develops.
My mother has told me that she feels terrible and guilty that I developed asthma that at times has literaly brought me to my knees. My parents never smoked, don’t drink, exercise, and eat in a healthy manner. We owned two dogs when I was a child. And I’m happy to report that I spent plenty of time playing in the dirt and gardening.
I feel it is unfair that readers feel it is appropriate to comment to articles like this by assuming that the mother must have been a smoker, a germ-a-phobe, or did something else “wrong.”
Maybe one day we will know what causes asthma and how to cure it, but don’t blame parents who have done the best they could and may have even done everything “right.”
— CGFFrom what I can understand about a mother giving birth through a C-section is that the child does not go through the birth canal; hence because of that the is no compression to the organs and they do not activate. The from that point it takes up to 6 months for the child’s organs to fully become activated. This might have something to do about the C-section statistics.
— Jeffrey Birnbaum Doctor of NaturopathicsInteresting. My niece, who was born both in the Fall and by C-Section, has asthma.
— JI#10 Kirstin: I’m a C-section mom and my kid was exclusively breastfed to six months (and continued to nurse thereafter). And he has asthma.
Don’t heap guilt on C-section moms by assuming we “choose” not to breastfeed and thus give our kids asthma. Or that we opted for our C-sections; they’re usually performed only when medically necessary. It’s clear you think we’re a bunch of lazy vain creatures who can’t be bothered to labor or breastfeed. But spare us the judgment, and don’t assume that breastmilk is the cure for all ills. It isn’t.
— LauraI agree with comment #8. Correlation does not necessarily mean causation. Based on the info in the article, it sounds like more research is needed to determine the actual cause of asthma. The apparent correlation to the Fall timeframe can help direct research.
The NYT would also do well to clarify that the 80% risk increase from C-sections is a “relative risk” increase, not an “absolute risk” increase (i.e., it’s not that over 80% of C-section babies get asthma).
— PhobosI have no idea how mothers these days cope with this kind of information.
“Your baby is at high risk for asthma if born by C-section and living in our ’sterile world’, so be sure to cover it with bacteria any chance you get and give your baby all the usual sicknesses to build up its immune system.”
“Your baby is at high risk for asthma if it gets exposed to infections as a baby, so be sure to take every hygienic precaution, hermetically seal it in a bubble and never let your baby get sick.”
I’m joking, but does anyone else notice how crazy this is? We obviously have no idea how this really works.
— dr. anonymous“Then why not scrape some of that there beneficial bacteria from the birth canal and lather it on the newly C-sectioned baby? –Susanna”
Susanna, have you any idea how long it is going to take for me to talk my uterus back down out of my thorax?
— Erin
Erin, sorry about your uterus. Maybe “scrape” was not the best choice of words; you could just use a spatula.
No, but I am perplexed by the infinite ingenuity of reason’s they come up with to promote vaginal births. In this particular case, the practical solution was just so obvious.
— SusannaHow does a respiratory infection prime an infant for asthma? Has the link been scientifically established, and if so, what’s the mechanism for it? I’m curious.
— HeronTwo kids born in October, both by c-section. Exclusively breastfed for 6 months, and continued nursing for 24-30 months longer. We get our share of the occasional cold, but no asthma, even though it runs in the family in mild to moderate form. I wonder to what extent breastfeeding plays a role, when you’ve got two strikes already against you!
— ChristieI emailed a colleague about the findings of this article. Here is his response:
“Matthew and Melanie were both born in the Fall. However, Matt was born vaginally, while Melanie was born by C section. Melanie had serious asthma for a couple of years as an infant and toddler — and still has a low grade case. Matt never did.”
Maybe it is a combination of things — the C section makes you more vulnerable, and something about the fall birth is what can tip you over into asthma. Vitamin D is a solid hypothesis, but so is the priming of the immune system with expsoure to bacteria. Among the bacteria to which those of us in the pre-asthma epidemic cohort were exposed were harmless ones in outside dirt — exposure to these also seems to confer protection against asthma. You start playing in dirt at a few months (or did when I was growing up). If you are born in winter, you can be playing in dirt (and sunlight) by perhaps May or June, that is, if kids are allowed to play in the dirt and grass any more.
— JohnWait, what?! Babies should be protected as much as possible from developing respiratory infections - which, apparently, are a function of that evil bacteria Daycare - because their immature lungs are damaged by them and they’ll subsequently get asthma.
On the other hand, that only applies to American babies, because babies born outside the US are less likely to get asthma - because they get more infections.
I know that it’s hard for laypeople (and, I assume, layjournalists) to sort through all these medical studies. But for heaven’s sake, the blatant contradiction in this article underscores how influenced by pre-existing prejudices we are (daycare makes our children sicker and weaker), and makes the article frustratingly incomplete. How are we supposed to reconcile these ideas? Are they irreconciliable? Are there other possible explanations for the results in either study (like Vitamin D deficiency, as another commenter proposed)?
— MelissaJaneClearly we should penalize Ob/Gyns who perform too many c-sections. Legally perhaps. Because they are totally irresponsible and causing rampant illness. Maybe if we levied a fine on mothers who selfishly failed to progress during labor, resulting in c-section, that would help too.
— S