Advantage, Osaka? Sports, health, and the realities of being the little sister
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Advantage, Osaka? Sports, health, and the realities of being the little sister
Being the younger sibling has accelerated tennis champions like Naomi Osaka and Serena Williams to greatness. But what does birth order mean for health? We serve up some data.
Source: Wikimedia Commons. Melbourne, Australia - 20 January 2020 - Naomi Osaka on Rod Laver Arena (Photo by Rob Keating)
In his upcoming book, Naomi Osaka: Her Journey to Finding Her Power and Her Voice, journalist and friend of this newsletter Ben Rothenberg illuminates the largely untold story of the early life and rapid ascent of four-time Grand Slam singles tennis champion and one-time #1 ranked women’s tennis player, Naomi Osaka.
In the book (which comes out next week in advance of Osaka’s much anticipated return to the Australian Open after a hiatus to give birth to her daughter) we learn that from a very young age, she was driven by a competitive tennis rivalry with her older sister, Mari.
If that sounds familiar, it should: Naomi Osaka’s greatest role model growing up was (and remains) Serena Williams, who also competed with her older sister, Venus, from a young age before becoming the legend she is today. Children who happen to be born as the younger sibling besting their older sibling in sports, of course, is nothing new. Rothenberg writes:
Many of the world’s greatest athletes started as the second best in their family. Having an older brother to challenge himself against, Michael Jordan said, gave him the fire and ferocity that became his signature on the court. “I don’t think, from a competitive standpoint, I would be here without the confrontations with my brother,” Michael said on The Last Dance. “When you come to blows with someone you absolutely love, that’s igniting every fire within you. I always felt like I was fighting Larry for my father’s attention… When you’re going through it, it’s traumatic. Because I want that approval, I want that type of confidence. So my determination got even greater to be as good—if not better than—my brother.”
Naomi said many of the same things in a 2021 Nike video she filmed alongside Mari. “My sister has been a driving force for me,” Naomi said. “The way my personality is, is probably a lot to do with her, because when I was little she would beat me every day.”
“Yep!” Mari chimed in, stopping Naomi mid-sentence.
“You just had to say something,” Naomi said, glaring with sisterly annoyance until Mari giggled.
“I feel like [losing to Mari] shaped my competitiveness a lot,” Naomi continued. “It just made me really want to win all my matches. That is a job that an older sibling doesn’t get enough credit for. So, definitely, I’m always really grateful for her, even though she’s annoying most of the time.”
Birth order is essentially random; there’s no reason one combination of parental genetic material would be systematically more likely to combine for a first child versus a second or third. Once born, of course, siblings are raised in different environments, with the most notable difference being that a younger sibling has an older sibling around to learn from, play with, and perhaps compete with. Taken as a group, what happens to first-borns, on average, is what we would have expected to happen to the second-borns had they happened to be born first, and vice versa.
Birth order in baseball
While a few examples of sibling rivalries in sports might come to mind, rigorously and systematically studying sibling athletes isn’t easy. But one study by researchers Frank Sulloway and Richard Zweigenhaft took advantage of Major League Baseball’s extensive record keeping to do an analysis of 700 total players, all of whom had brothers who also played in the MLB (the study was highlighted in The Best: How Elite Athletes Are Made by Tim Wigmore and Mark Williams).
After accounting for when they were called up from the minor leagues to the major leagues—where one less-talented brother might make it into the major leagues in part off the reputation of their more-talented brother—Sulloway and Zweigenhaft found that younger brothers outperformed older brothers on a few metrics: they were better batters overall, were more likely to hit home runs, and more likely to take risks and (successfully) steal bases.
Younger brothers also tended to have longer careers by about 2 years. When looking at brothers who played the same position, they found that when players were close in age (less than 5 years apart), younger siblings tended to have longer careers than when they were farther apart in age, suggesting the more highly competitive atmosphere of a close sibling rivalry could really make a difference in a baseball career.
If having siblings around is enough to shape the career of a professional athlete, is it enough to impact health?
Birth order effects on health
Studying the effect of birth order on health is challenging, since any differences might take decades to manifest, and collecting health data across large numbers of families is no easy feat.
In Sweden, however, such research is a bit easier. The country has been collecting health and genealogical data on its population for generations; their registries have been referred to as “a goldmine for epidemiological research.”
One reason such data are so valuable for studying siblings is that researchers can compare them while being able to easily account for the characteristics those siblings have in common by nature of being raised in the same household—things like a family’s income, geographic location, or parent’s education level that might impact health outcomes—by doing “within-family” comparisons across many families.
In a study looking at Swedish families with more than one child born to the same two parents, researchers Kieron Barclay and Martin Kolk found that among about 1.8 million siblings born between 1938 and 1960, higher birth order (meaning, being a younger sibling) was associated with higher mortality rates in the ensuing decades, more pronounced for third-and-later-born children and women.
Source: Barclay, K. and Kolk, M., 2015. Birth order and mortality: a population-based cohort study. Demography, 52(2), pp.613-639.
Looking at causes of death, increasing birth order in men was associated with higher odds of death by accidents/trauma/suicide. In women, increasing birth order was associated with higher odds of death for those same causes as well as for cancer. Meanwhile, there were insignificant reductions in odds of death of cardiovascular disease with increasing birth order.
In another study using similar data from Sweden, researchers Evelina Björkegren and Helena Svaleryd looked at millions of Swedes across the entire lifespan. They found that relative to first born children, second- and later-born children were less likely to be hospitalized at a young age, but by the time they reached adolescence, they became more likely to be hospitalized—including at older ages, in keeping with the above mortality results.
Source: Björkegren, E. and Svaleryd, H., 2023. Birth order and health disparities throughout the life course. Social Science & Medicine, 318, p.115605.
When it came to specific causes for hospitalization, younger siblings seemed to always be at increased risk for injury visits, but it was in adolescence when disparate rates of mental illness took off for non-first-born children—specifically for substance use disorders. Meanwhile, first-borns were more likely to receive outpatient treatment for ADHD, depression, and anxiety than their later born siblings.
Source: Björkegren, E. and Svaleryd, H., 2023. Birth order and health disparities throughout the life course. Social Science & Medicine, 318, p.115605.
Why?
We’ve only looked at some small slivers of this question of the effects of birth order over the lifespan, and only a small bite of data from baseball and Sweden.
But outside of health, a growing body of research shows birth order effects on educational achievement and future earnings, with advantages for first-borns. Within health, smaller studies suggest differences in all sorts of diseases. Many of these differences have a number of different possible explanations, ranging from differences in the womb environment to diminishing parental and educational resources for younger siblings as more children enter the household. In all likelihood, differences between siblings are going to be driven by a combination of factors.
To bring this all together, perhaps whatever sets up younger siblings for worse health outcomes are some of the same factors that predispose them to be able to best their older siblings in sports. The original purpose of the baseball study above was actually to look at risk-taking behaviors in sports, also finding that younger siblings were more likely to participate in higher risk sports (e.g. football, rugby, boxing, skiing, scuba diving) than their first-born siblings—stealing bases and slugging for home runs in baseball was identified as part of this risk-taking behavior. That same risk-taking behavior might explain some of the differences in hospitalizations for injuries and substance use seen in the Swedish data.
We won’t pretend to know the answers here, and as parents of two kids for each of us, it’s humbling to think about what the differences in our kids’ upbringing might mean for them later on. Naomi Osaka, Serena Williams, and Michael Jordan made being a younger sibling work to their advantage—at least professionally—but not every younger sibling will be able to do that.
To all of you—many of whom are presumably siblings yourselves—what do you think of all this? Are there any other high quality data that might confidently answer some these questions? Or, what other ideas come to mind? Let us know in the comments below!
