Tuesday, July 10, 2012

Childhood Asthma: Kids Born to Mothers Who Consume Semi-Skimmed Milk 8% More, Offspring of Whole Milk Drinking Mothers 15% Less Likely to Develop Asthma

Image 1: Better make sure your "mother's milk" (the milk you drink while you or your significant other are pregnant) is full fat!
I don't know if you have listened to my "brother" Carl Lanore's Super Human Radio interview with Boyd Eaton, yesterday, but if you did, you will probably remember that the two also broached the issue of dairy consumption on a paleo diet. And while many of you may have been surprised to hear that Eaton does consume milk products on a regular basis, it is probably even more intriguing that the show came full-circle only a couple of minutes later, when Carl who had just addressed the issue of iron-overload and how that relates to the relative abundance of meat in an ancestral diet, read my facebook message about the beneficial effects of milk proteins, Zunquin et al. observed in a 2006 trial rodent trial intended to simulate the potential side effects of high dose iron supplementation to replete iron stores in iron-depleted athletes (Zunquin. 2006).

Milk allergy or allergy due to the lack of full-fat milk - is that the question?

Yet while the Zunquin study is by no means the only scientific evidence that nature's original meal replacement, irrespective of whether or not it may be "intended for human consumption" can exert potent health effects (cf. Barfray. 2003), the pros and cons of a high(er) intake of dairy is still a matter of constant debate. Other than within the paleosphere, the public and scientific debate does yet usually revolve around the notion of low- vs. high fat dairy, with the common recommendation to "choose low fat dairy in order to avoid the unhealthy saturated fats that come with the full-fat variety".
Figure 1: Associations between mothers' consumption of milk and dairy during pregnancy and incidence of early childhood asthma (18 months) in children from the Danish national Birth Cohort; data expressed as differences to no-consumption (data based on Masolva. 2012)
Aside from the downside of non-existent yet potentially healthy levels of certain fatty acids, such as conjugated linolic acid (yeah, the one that can kill empty fat cells, cf. "Nasty Insights into the Yo-Yo-Effect: Lower Body Fat Sticks and From Fit2Fat There's no Easy Way Back!"), the reduced absorption and presence of fat-soluble nutrients and the necessity to add sugar or artificial flavors, as well as chemicals to modify the taste and mouth-feel of those watery low-fat dairy products, a recent study from Department of Nutrition at the Harvard School of Public Health in Boston does now provide compelling evidence that either one or all of the former aspects, or a hitherto not elucidated difference between skim and full-fat dairy products increases children who are born to mothers who consume >5 portions of semi-skimmed milk per week during their pregnancy have an 8% increased risk of developing childhood asthma and a 40% increase in risk of developing allergic rhinitis later in life (Maslova. 2012).

Table 1: If you are interested in other sources of CLA (and omega-3), in general, and the difference between grass- and grainfed beef, in particular, check out this table from a Daley et al. (Daily. 2012)
What's even more intriguing, though, is that the consumption of equal amounts of full fat milk was associated with a statistically significant 25%(!) reduction in asthma-risk (and recurrent wheeze symptoms) in the ~60,000 children / mother pairs from the dataset of the Danish National Birth Cohort the US scientists analyzed. Similarly, there was a
"dose–response was present for semiskimmed milk intake, while any intake of full-fat yoghurt appeared to be protective of child asthma" (Maslova. 2012)
that did, just as the aforementioned results, remain significant, even when the data was adjusted for the intake of other allegedly beneficial foods (fruit and vegetables) and nutrients (vitamin E, vitamin D, Se, Zn from diet and supplements).

So are those the CLAs and other ruminant trans-fats?

While Malsova et al. fail to give a clearcut answer on what the underlying reasons for these observations are, their detailed analysis of the data does yield some evidence that CLAs and other ruminant trans-fatty acids cannot explain the differences, as they showed similar correlations with both full-fat and semi-skimmed milk intake and were "not associated with either the early or later childhood outcomes" (Maslova. 2012).

Image 2: Not, not all full-fat milk drinkers worked on a farm ;-)
An analysis of other potentially confounding lifestyle factors yielded similarly inconclusive results so that this leaves us without a causal explanation for either the protective effect of whole milk and full-fat yogurt intake on early childhood asthma or the increased risk to develop wheeze at 18 months in children born to high consumers of semi-skimmed milk. In the absence of any information of what happened in the course of the following 7-years it appears futile come up with any hypothesis that would explain the direct associations of maternal low-fat yoghurt consumption with child asthma and allergic rhinitis and the "suggestive" relationship of the latter with total milk intake, anyways. And as the scientists say:
The diversity and complexity of our results make it difficult to interpret and propose a single agent mechanism, yet the consistent associations with low-fat yoghurt for later childhood outcomes suggest that compounds specific to this food, such as artificial sweeteners, may play a role.
Interestingly, they specifically refer to the use of aspartame as the "primary" artificial sweetener in the Danish food supply since the 1980s, but cite a - at least in my humble opinion - highly biased source (Gideon. 2010) on that issue without even providing a single scientific study that would implicate aspartame as a factor involved in the etiology of asthma (+my brief research shows, there is none).
Image 3: Too much statistical shenanigan involved in the ER data for my liking.
A note on additional data evaluated in the study: The scientists make use of the actual hospital admissions due to asthmatic reactions as another source for their study data. Unfortunately, those only contribute to the already confusing results, because they suggest that despite the fact that the incidence of early childhood asthma is lower (other data), the chance to end up in hospital, as assessed by data from the Danish National Patient Registry appears to be higher in children born to mothers with a high full fat milk intake (+30%), and minimally reduced for children whose mothers consumed the same amount of skimmed dairy - it is however questionable how reliable this 3rd hand data which had to be linked back to the central person registry first and ran through multiple processing steps actually is (same for data from the Register of Medicinal Product Statistics).
As far as the underlying mechanisms are concerned this leaves us with but one relatively certain conclusion: The scientists' initial hypothesis that ruminant trans-fatty acids could play a causal role in the development of allergic disease development cannot be upheld in view of the inverse associations Maslova et al. found between the CLA content and the risk to develop asthma and/or allergic rhinitis across products with different fat content.

Suggested reading:

  1. Bartfay WJ, Davis MT, Medves JM, Lugowski S. Milk whey protein decreases oxygen free radical production in a murine model of chronic iron-overload cardiomyopathy. Can J Cardiol. 2003 Sep;19(10):1163-8. 
  2. Daley CA, Abbott A, Doyle PS, Nader GA, Larson S. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutr J. 2010 Mar 10;9:10.
  3. Gideon B (2010) Aspartam: Nu også i ikke ‘Light’ produkter. < http://infowars.dk/content/aspartam-nu-ogs%C3% A5-i-ikke-light-produkter > last accessed on July 10, 2012
  4. Maslova E, Halldorsson TI, Strøm M, Olsen SF. Low-fat yoghurt intake in pregnancy associated with increased child asthma and allergic rhinitis risk: a prospective cohort study. Journal of Nutritional Science (2012), vol. 1, e5.
  5. Zunquin G, Rouleau V, Bouhallab S, Bureau F, Theunynck D, Rousselot P, Arhan P, Bougle D. Iron and exercise induced alterations in antioxidant status. Protection by dietary milk proteins. Free Radic Res. 2006 May;40(5):535-42.