Heat-treated milk product consumption during infancy may increase asthma risk
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Infants with high consumption of infant formula and other strongly heat-treated milk products demonstrated increased risk for asthma, according to a study published by Pediatric Allergy and Immunology.
“This is, to our knowledge, the first study to show that high consumption of strongly heat-treated (high-pasteurized at greater than 100°C or sterilized) milk products may be associated with an increased risk for asthma,” author Katariina Koivusaari, MS, doctoral candidate at University of Helsinki in Finland, told Healio. “This group includes infant formulas, the consumption of which was also associated with an increased risk. Breastfeeding has been previously associated with a decreased risk for nonatopic asthma in several studies.”
To study the association between the consumption of differently processed milk products and asthma risk, Koivusaari and colleagues evaluated data of 3,053 children born between September 1996 and September 2004 who were included in the Type 1 Diabetes Prediction and Prevention Nutrition Study and had information on whether they had asthma and when it was diagnosed.
Researchers evaluated 3-day food records from the children, which were collected at age 3 months and 6 months, and at 1, 2, 3, 4 and 5 years. The researchers then classified each milk product consumed according to their adopted heat treatment and homogenization.
Using a joint model for longitudinal and time-to-event data, the researchers analyzed the associations between the risk for asthma — including atopic asthma (IgE positive to at least one of the tested allergens), nonatopic asthma (IgE negative) and all asthma — and the amounts of different milk products that the children consumed.
Overall, 184 (6%) of the children were diagnosed with asthma by the age of 5 years, with 101 (54.9%) cases of atopic asthma, 75 (40.8%) cases of nonatopic asthma, and eight (4.3%) cases that could not be categorized due to a lack of IgE results.
The median age at asthma diagnosis was 3 years (interquartile range [IQR], 2-3.5 years) for atopic children and 2 years (IQR, 1-3 years) for nonatopic children.
The researchers found an association between consumption of milk-based infant formulas and an increased risk for all asthma (HR = 1.15; 95% CI, 1.07-1.23) and nonatopic asthma (HR = 1.23; 95% CI, 1.13-1.34), with a weaker association between consumption of strongly heat-treated milk products and risk for all asthma (HR = 1.06; 95% CI, 1.01-1.1).
Also, high consumption of all cow’s milk products had a borderline association with risk for all asthma (HR = 1.04; 95% CI, 1-1.08) and a significant association with nonatopic asthma (HR = 1.09; 95% CI, 1.03-1.15).
There was an association between consumption of nonfermented milk products and an increased risk for nonatopic asthma (HR = 1.08; 95% CI, 1.02-1.14), but this association did not persist in an analysis that excluded infant formulas.
The researchers considered infant formulas strongly heat-treated milk products, which also were associated with an increased risk for nonatopic asthma (HR = 1.08; 95% CI, 1.02-1.15). Because the association between strongly heat-treated milk product consumption and risk for all asthma persisted when infant formulas were excluded, the researchers concluded that the risk may stem from the heat treatment itself.
“In our study, the association between infant formulas and asthma were likely mostly seen for the nonatopic, not the atopic, type of asthma. Similar risk associations did not appear for pasteurized (ie, more mildly heat-treated) milk products,” Koivusaari said.
Separate Cox proportional hazards analyses for each food record collection age point revealed an association between consumption of all cow’s milk products and an increased risk for nonatopic asthma at the age of 3 months and 6 months and at 1 year, but not later. However, there were no associations for all asthma or atopic asthma.
Additionally, the researchers found no associations between the amount of breastmilk consumed and nonatopic asthma or other outcomes, although HRs trended slightly toward protective.
The researchers cautioned that the association between infant formula consumption and increased risk for nonatopic asthma should be interpreted with moderation because breastmilk and infant formula are complementary feeding methods.
Finally, the researchers didn’t find any associations between fermented milk product consumption and asthma, nor did the study evaluate the consumption of nonanimal milk products.
“As far as I know, there is insufficient evidence that plant-based milk alternatives would modify the risk for asthma,” Koivusaari said.
“Breastfeeding is considered the gold standard of infant feeding. Our study does not give any reason for recommending alternative, hydrolyzed or soy-based formulas,” she added.
Overall, the researchers concluded that heat treatment plays a role in the association between milk consumption and asthma and that their results show that strongly heat-treated milk may be a risk factor, although they also acknowledged that more research is needed.
“Further studies are needed to confirm the findings of our study before any results can be implemented. As our study was observational, it does not provide evidence on a direct cause-effect relationship,” Koivusaari said. “Also, it would be important to identify the milk components that play a role in the immunological associations, either in a positive or negative way. A better understanding would enable development of infant formulas with possibly more suitable processing methods.”