NEW YORK (Reuters Health) – Breastfeeding is often advocated as a way to help prevent allergies in babies at high risk, but a new study finds that infants breastfed for longer periods may actually be more likely to develop the allergic skin condition eczema.
The study followed 321 infants who were at increased risk of allergies because their mothers had a history of asthma. Researchers found that among those who were breastfed exclusively for more than six months, 55 percent developed eczema by age 2.
That compared with 37 percent of those breastfed exclusively for three to six months, and 29 percent of babies given breast milk alone for less than three months.
On the other hand, the babies were less likely to develop wheezing symptoms as long as they were still being breastfed. Wheezing — difficult breathing marked by a high-pitched whistling sound — is a common symptom of respiratory infections in infants and young children because their airways are so small; but it can also be a marker of an increased asthma risk later on.
Exactly why breastfeeding had different associations with eczema and wheezing is not certain. But several previous studies have found a similar pattern.
Taken together, the findings suggest that extended breastfeeding should not be recommended as a way to prevent eczema in high-risk babies, Dr. Hans Bisgaard and colleagues at the University of Copenhagen in Denmark write in the Journal of Allergy and Clinical Immunology.
That does not mean, however, that women with a history of allergies or asthma should avoid breastfeeding, according to Bisgaard. “There are many good reasons why the mother should breastfeed her child,” he told Reuters Health in an email.
Breast milk is considered the best, most balanced form of nutrition for infants, and experts generally recommend that babies be breastfed exclusively for the first six months of life.
As for why longer breastfeeding might contribute to eczema in high-risk babies, it’s possible, according to Bisgaard’s team, that mothers with allergies can transmit a “risk factor” for eczema through their breast milk — such as antibodies or other immune system substances that promote the allergy.
The fatty-acid makeup of the breast milk could also be a factor, the researchers note. In a previous study of the same group of mothers, Bisgaard’s team found that the women’s breast milk generally had lower levels of omega-3 fatty acids than that of mothers without allergies; there is some evidence that omega-3 fats are protective against allergies and asthma.
There was no strong evidence from the current study, however, that the fatty acid content of mothers’ milk was important in eczema risk. “Therefore, follow-up studies regarding other possible immune modulating factors are planned,” Bisgaard said.
The current findings are based on 321 children who were followed starting at the age of 1 month. Their parents kept diaries to record any “wheezy episodes” — defined as three consecutive days of the breathing problem — and cases of eczema were diagnosed by the researchers.
Overall, 69 babies were breastfed exclusively for less than three months, 203 for three to six months and 49 for more than six months.
When the researchers accounted for a number of factors in eczema risk — including birth weight, parents’ history of eczema and the presence of a cat or dog at home — babies who were still being exclusively breastfed between the ages of 6 and 9 months were more than six times more likely to develop eczema by age 2 than those who were no longer being fed breast milk alone.
When it came to wheezing, the majority of the babies — 262 — had at least one episode. However, babies who were still being exclusively breastfed had a one-third lower risk than infants the same age who had stopped.
Breastfeeding, according to Bisgaard’s team, may help reduce wheezing episodes by protecting babies from respiratory infections — the primary cause of wheezing that early in life.
Because all of the mothers in the study had a history of asthma, the findings cannot be generalized to other women, Bisgaard said. Further studies are needed to better understand how longer breastfeeding might affect average-risk babies’ odds of eczema or wheezing, according to the researcher.
SOURCE: Journal of Allergy and Clinical Immunology, March 2010.