Season of birth may be associated with risk for adult-onset asthma
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People born between January and June in Finland experienced a higher risk for adult-onset asthma than people born later in the year, with a stronger risk among people with atopic asthma, according to a letter published in Asthma.
Led by Anni Koskinen, MD, PhD, docent in the department of otorhinolaryngology-head and neck surgery at Helsinki University Hospital and University of Helsinki, the researchers assessed data of people born between 1906 and 1966 from Finnish national registers.
The population included 1,247 adults aged 30 years and older with adult-onset asthma who were matched for gender, age and living region with one or two controls from a population of 1,970 (total population: mean age, 54 years; standard deviation, 12; age range, 31-91; 37% men).
The researchers assessed information about known risk factors for asthma, including parental asthma and allergy, BMI, professional training, number of siblings, being the first child, allergic rhinitis, allergic conjunctivitis and atopic dermatitis.
Asthma and severe asthma were the only factors that were associated with birth between January and June, the researchers found, adding that these participants were at higher risk for adult-onset asthma with an overall odds ratio of 1.33 (95% CI, 1.11-1.54), with this finding remaining significant for women (OR = 1.4; 95% CI, 1.17-1.68) but not men (OR = 1.16; 95% CI, 0.92-1.47).
The researchers found similar associations between birth season and adult-onset asthma based on its known risk factors.
For example, among patients born between January and June, odds ratios included 1.29 (95% CI, 1.03-1.62) for those participants who did not have one or more allergic disease, including allergic rhinitis, allergic conjunctivitis and AD, and 1.36 (95% CI, 1.12-1.65) for those who did.
Also, these associations were consistent between participants who did and did not have numerous respiratory infections before and after they were of school age; between those who were raised on a farm, in the countryside or elsewhere; and between those who only completed primary school or less and those who completed further education.
Further, these associations between season of birth and adult-onset asthma persisted among participants who were born between 1948 and 1946 (OR = 1.61; 95% CI, 1.23-2.06) but not for different birth periods.
Also, these associations persisted for participants with a BMI less than 25 kg/m2 or between 25 kg/m2 and 30 kg/m2, for those who had no parental asthma and allergy, those who had professional training, those with two siblings or more and those who were the first child.
Considering previous work indicating positive associations between adult-onset asthma and number of allergic comorbidities, with more pronounced associations for later birth cohorts and females, the researchers wrote that season of birth may have a stronger effect on increasing asthma risk among patients with atopic asthma.
The researchers further hypothesized that these associations between season of birth and chronic inflammatory disease may be due to weight, sun exposure, vitamin D metabolism and infection risk, although they cautioned that more research would be necessary.
But overall, the researchers concluded, these findings strengthen earlier research indicating the role that early life events have in adult-onset asthma.
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Christopher O'Brien, MD, PhD, FCCP
The article by Koskinen and colleagues represents another interesting addition to the literature evaluating association of season of birth with respiratory diseases that can manifest both in childhood and in adulthood.
This study is a strong example of the opportunity that large multidomain population databases afford in the effort to develop testable hypotheses on factors impacting early immunologic development, tolerance and pulmonary development and the sometimes surprising influence such factors have on diseases manifesting in adulthood.
As the authors note, an association between season of birth and childhood asthma has been previously described. This work extends these findings, leveraging a large population registry in Finland, and yields the fascinating observation that adult-onset asthma (age > 30 years) is also associated with season of birth, with higher rates seen during January through June.
This was particularly evident in the youngest group, females, those who were the first child, those with no asthma/allergy family history, those with no obesity (BMI ≤ 30 kg/m2), those who have several siblings and those who have professional training.
Although further research will be necessary to assess causality and understand underlying pathologic mechanisms, as practitioners, findings such as these remind us of the importance of counseling both patients and caregivers on modifiable risk factors early in life, including exposure to secondhand smoke, viral infections and others, as they can have long lasting implications on risk for developing respiratory conditions such as asthma decades later.
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Although this is an interesting concept and may catch the eye of the public, I am not sure about its relevance in the big picture.
As the researchers state, this study contradicts a previous study. So, unless it is looked at in a more widespread study from multiple locations, its relevance is still unclear. Also, unless one could correlate the reason, such as increased viral infection or pollen exposure in the first 6 months of life, then I still do not know what significance this holds.
And because most pregnancies probably are not timed, unless we could find a definitive connection, these associations will not change and maybe never would anyway.
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