Season of birth affects adult risk of allergy

By John Murphy, MDLinx
Published March 22, 2016

Key Takeaways

People born in autumn are significantly more likely to have eczema than those born in spring, according to a study published online March 12, 2016 in Allergy.

Although researchers have known for some time that the season of the year in which you’re born and your risk for allergy are related, they haven’t understood the biological mechanisms to explain it. This new study offers an explanation of how a one-time exposure like the season of birth can have a lifelong effect.

“These are really interesting results,” said study co-author John Holloway, PhD, Professor of Allergy and Respiratory Genetics at the University of Southampton, in Southampton, UK. “We know that season of birth has an effect on people throughout their lives. For example, people born in autumn and winter are [generally] at increased risk for allergic diseases such as asthma. However, until now, we did not know how the effects can be so long lasting.”

To find out, the researchers examined how gene transcription—in particular, epigenetics—plays a role in the association between season of birth and allergy. Epigenetics refers to heritable alterations in gene expression (turning genes “on” or “off”) caused by mechanisms other than changes in the DNA sequence itself.

The researchers conducted an epigenome-wide association study (EWAS) on DNA samples from a cohort of 1,456 people born on the Isle of Wight from 1989 to 1990. They found that particular epigenetic marks—from DNA methylation—were associated with season of birth and still present 18 years later.

The research team was also able to link birth-season DNA methylation to allergic disease; for example, people born in autumn had greater risk of eczema compared to those born in spring. The researchers then validated the results in a cohort of Dutch children.

“Epigenetic marks are attached onto DNA, and can influence gene expression for years, maybe even into the next generation. Our study has linked specific epigenetic marks with season of birth and risk of allergy,” Dr. Holloway said.

“However, while these results have clinical implications in mediating against allergy risk, we are not advising altering pregnancy timing,” he added.

The researchers also found that birth season-associated DNA methylation was largely absent in newborns, which suggests that it arises postnatally.

Further research is needed to better understand how different seasons of the year lead to altered disease risk, and whether specific differences in the seasons—including temperature, sunlight levels, and diets—play a part, the researchers noted. More study is also needed on the relationship between DNA methylation and allergic disease, and whether other environmental exposures also alter the epigenome with potential disease implications.

“It might sound like a ‘horoscope by the seasons,’ but now we have scientific evidence for how that ‘horoscope’ could work,” said the study’s first author Gabrielle Lockett, PhD, Postdoctoral Research Fellow at the University of Southampton. “Because season of birth influences so many things, the epigenetic marks discovered in this study could also potentially be the mechanism for other seasonally influenced diseases and traits too, not just allergy.”

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