In his book “Outliers,” Malcolm Gladwell describes “relative age effect,” which has been observed in athletics, academia, and other fields where participation is higher among those born early in the applicable selection period and lower among those born later in that period.
He uses the example of Canadian youth hockey, referencing the work of a Canadian psychologist who found that a disproportionate number of star hockey players in the country were born in the first six months of the year. Canada’s cutoff for junior hockey is January 1. “A boy who turns 10 on January 2, then, could be playing alongside someone who doesn’t turn 10 until the end of the year,” Gladwell notes in the book. There have been other cases where being born at a certain time helps someone get a head start, but could being born a certain time put you at a health disadvantage, too?
A team led by Penn Medicine’s Mary Regina Boland, PhD, an assistant professor of Informatics in Biostatistics, Epidemiology and Informatics, looked at previously documented associations between specific diseases and being born at a certain time of the year, probing deeper to pinpoint the links between them.
In a Journal of the American Medical Informatics Association study, Boland’s team looked at data from 10 million patients across six sites – two in New York City, and one each in Nashville, Seattle, South Korea, and Taiwan – to identify the main drivers behind these associations.
“Instead of saying cardiovascular disease is correlated with being born during the winter, we can now say the main driver for that association is increased exposure to fine air particulates during the first trimester of pregnancy that increases the risk of atrial fibrillation,” Boland said. “We can now drill deeper to get at a firmer explanation for why those associations exist.”
A large sample size drawn from the United States, Taiwan, and South Korea groups enabled the team to look at the effect of relative age on health and disease. In this research, they tested 133 different diseases and found only one was statistically significant according to relative age: those younger than their school peers were at about 18 percent higher risk for attention deficit hyperactivity disorder compared to the rest of their peers.
Other studies have described the relationship between relative age and ADHD, but the new study is the first to investigate relative age and disease across three distinct countries, six sites, and four distinct school cutoff dates. The team found more confidence in this higher risk as this association was observed to be higher in Taiwan, where all kids are on the same educational timeline, and a smaller association was found in the United States sites, where a mix of public and parochial kids can experience the effects of different cutoff dates for school enrollment.
The team’s methods looked at maternal exposures – things that moms experience during pregnancy --that can influence an offspring’s lifetime disease risk, as well as how newborns’ direct exposure to different climate attributes, such as precipitation, sunlight, and pollutants, like fine air particulates and carbon monoxide, may influence their risk of disease later in life.
Their findings included a link between first-trimester exposure to carbon monoxide and increased risk of depressive disorder. Second, a link between first-trimester exposure to fine air particulates – such as those found from factory pollution observed in greater levels in the Korea and Taiwan sites -- and increased risk of atrial fibrillation – a heart rhythm irregularity – later in life. Thirdly, they found a connection between decreased exposure to sunlight during the third trimester and an increased risk of type 2 diabetes.
“These findings offer valuable implications for care of expectant mothers,” said Nicholas P. Tatonetti, PhD, an assistant professor of Biomedical Informatics at Columbia University and senior author of the research. “For example, by identifying the related causal risk factors in these disease pathways, we are able to identify areas that may require seasonal dosing of prenatal supplements.
Despite the adage that “age is just a number,” it seems scientific research is mounting to prove there is in fact a lot more to it.