Youngest? Eldest? Or in the middle? How birth order affects your health

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You’ve probably heard the received wisdom about personality being linked to birth-order. Firstborns are bossy, the youngest out of a brood may be the entertainer, only children are self-possessed, and so on.  However, a growing body of research has shown it’s not just about character-traits. Studies have revealed that our place in the family has an impact on health and wellbeing. The reasons for this are complex - they're connected to family resources, parental attention and exposure to other children's germs, which impacts immunity. But there ARE some interesting patterns that emerge when it comes to birth order and health. Recognise any of these from where you are placed in the family hierarchy?


  • The eldest is more likely to be taller. All that attention and good nourishment is believed to help promote growth.
  • Firstborns have higher IQs on average. Firstborns score higher than their siblings in IQ tests as early as age one. Researchers found that parents changed their behaviour as subsequent children were born. They offered less mental stimulation to younger siblings also took part in fewer activities such as such as reading with the child, crafts and playing musical instruments.
  • Mothers also took higher risks during the pregnancy of latter-born children, such as increased smoking.
  • Eldest children of the family are more at risk of heart disease, diabetes and hypertension: With first babies, the placenta isn’t as efficient so fewer nutrients may be transmitted as with subsequent pregnancies; firstborns tend to have lower birthweight. This may have a long-term impact - a study at the Fondazione Don Carlo Gnocchi in Milan found that first-borns could face up to a 60 percent increased risk of developing heart disease compared to their siblings. Research from University of Auckland in New Zealand published in the Journal of Clinical Endocrinology & Metabolism shows first-borns are more likely to suffer from high blood pressure and have more trouble absorbing sugar which puts them at greater risk of diabetes or related problems.
  • Research shows higher asthma rates in firstborns, and a survey in Japan found they’re more prone to allergic rhinitis (hay fever or seasonal allergies). Again this may be linked to the condition of the uterus before the first pregnancy. Plus many (overprotected) firstborns may not get exposed to bacteria or viruses until they start school; younger siblings battle the bugs older siblings bring home, so may develop stronger immune systems. 

The middle child

  • Middle children have better immunity This is as a result of having to fight off the bacteria your elder siblings brought home (and you’re 5% less likely to suffer gum disease as a result)
  • Middleborns are more likely suffer fatigue. Research from the University of Medicine and Dentistry of New Jersey suggests that middle children are slightly more likely to suffer from Chronic Fatigue Syndrome than their younger or older siblings. Although, statistically, middle-borns are the least likely to seek psychological help, when they do, it tends to be for symptoms of depression or anxiety - such as tiredness, a lack of direction, panicky feelings and a sense of gloom about the future. 
  • Being in the middle means more likliehood accidents. According to the Department of Behavioural Science, University of Minnesota-Duluth third and fourth-born children have a higher incidence of accidents that result in hospitalisation!  This may come down to parents’ attention being spread thinly when there are more children to attend to.


  • Better immunity for the youngest. They should thank their siblings for their germs. (Just as well – they’re less likely to have been immunised as young children than their siblings according to London research – the chances of being immunised decreases by 20% for each child!).    
  • The youngest seek danger. The personality and Social Psychology Review found that later-borns children were 1.48 times more likely to participate in dangerous sports than firstborn, and last-borns are more likely to be thrill seekers and adrenaline junkies and take the danger option in sports. One theory is that this is because parents tend to relax the boundaries with each successive child — so the last-born will have the least limits, and therefore be liable to take the riskiest options! 
  • Being born last may give addictive habits. One study from the University of Oklahoma  found that children go through puberty on average three months earlier than their older siblings, and early puberty has been linked to increase in dangerous behaviours – such as smoking. 
  • The youngest in the brood will generally be smaller when grown up (and possibly the fattest). According to data from the respected Children of the Nineties health study which looked at growth rates up to the age of ten, those in larger families tending to be shorter than average, and the youngest child the shortest of all on reaching their tenth birthday. 

The Only Child

  • Only ones are content. Unlike children in larger families, only children are unlikely to lose the fond and exclusive attention of either parent. Being showered with love and approval helps them develop a healthy level of self-confidence. And there are advantages of growing up without brothers and sisters - research from the University of Essex reported that only children experience less bullying.  They’re more contented as teenagers, research shows.
  • Only kids may be overweight: According to research from the University of Gothenburg, only children have a 50 per cent higher risk of being overweight. This may be because they don’t run around with siblings, and may be more sedentary – more likely to have TVs or computers in their bedrooms. Plus, parents of only children may feel the need to overindulge, and without having to share - they get 100% of the resources (food).
  • Perfectionism is an issue for family singletons. ‘When we’re growing up, it’s natural to compare ourselves to those around us,’ explains psychologist Linda Blair in her book Birth Order. ‘Given that there’s usually a preponderance of admiring and encouraging adults in the single’s life it means they set their standards in relation to them. You’ll almost certainly shoot high and expect a deal of yourself. This may make you prone to burnout and other disorders that result when the pressure is unrelenting.’ 
  • Singles children are at greater risk of OCD. According to Linda Blair, only children tend to grow up with little experience of how to cope with disorder and confusion – having an adult constantly on hand. ‘In fact, my clinical experience suggests that only children are also more prone than others to obsessive behaviour - they need to keep everything precisely in order.’ 

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