Do Younger Siblings Tend To Be Healthier Than Their Elder Siblings?

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Turns out younger siblings have a lot more to be thankful for than just hand-me-downs and relaxed parents! The big brother or sister may have done them a huge favor and triggered a more beneficial immune system to counter certain diseases. We are yet to know exactly why, but it's a fascinating line of research.

Every family has sibling stories they bombard unsuspecting houseguests with – stories about how different each child is, in spite of being born and raised under the same roof! And in their defense, they may not be the only ones who are puzzled. Scientists are equally curious about the complex world of siblings. You only have to look at the numerous studies – on personality differences, intelligence levels, obesity issues, among others – to see this. The latest idea to emerge is that the second child may actually benefit from the first child’s allergies.

Second Time Lucky

Interesting work is going on in the space of sibling effects, including health implications. Scientists are looking into how the first pregnancy affects the mother’s immune system and if and how the benefits may be passed on to the next child.

One study, on the mechanisms that led to siblings having a lower risk of childhood asthma and allergy, looked at infants less than four weeks old and the immune response in their airways. Taking a step back, an immune response is how the immune system reacts to an antigen. It’s a complex interplay between the antigen, B and T lymphocytes, and non-specific defenses. The response could be beneficial, indifferent, or injurious. The study showed that infants with a sibling had a significantly more beneficial immune response in their airways and, hence, countered allergies and hay fever way better. The response was also better when the gap between the births was smaller. The study confirmed the presence of an early immune modulatory effect in siblings and pointed out that the fascinating sibling synergy needed further exploring.1

Similarly, a British study, examining contributing factors in common ailments like hay fever, showed that family size and position of the child played a key role, along with factors like personal hygiene. The presence of an elder sibling significantly tilted the charts in favor of the younger one having a lower incidence of hay fever and allergies. Apart from the role the mother’s immune system played in transferring this advantage, it was also partially attributed to the younger ones simply being exposed to more dirt and germs – and hence building stronger immunity – because of having another child in the house!2

Younger And Fitter?

In one study of Swedish sibling pairs, the elder sibling was found to have a greater BMI and tendency to be obese than the younger child.3

That’s not all! The elder ones could also be more prone to immune-mediated diseases.4 As one study showed, firstborns were more prone to diabetes and cardiovascular disease later in life. They were found to have greater insulin sensitivity and higher day-time blood pressure than their younger siblings.5

The Unexplained Why

While studies and data seem to indicate that the second and third child will have it a lot easier health-wise, the full story is yet to emerge. The “why” of it all is still open to many interpretations and definitely needs more deep dives. Yet, the results of study after study are hard to ignore, piquing scientists’ interest in this in-utero programming of the immune system. How, after all, does the mother’s body recognize this is the subsequent pregnancy and gear up to “reward” the fetus? And an outlandish thought – can we program the mother’s body to assume even the first pregnancy is number 2 or 3 and thus heap the same benefits on the firstborn? Watch this space as research hots up!

References   [ + ]

1. Wolsk, Helene Mygind, Bo L. Chawes, Nilofar V. Følsgaard, Morten A. Rasmussen, Susanne Brix, and Hans Bisgaard. “Siblings Promote a Type 1/Type 17‐oriented immune response in the airways of asymptomatic neonates.” Allergy (2016).
2. Strachan, David P. “Hay fever, hygiene, and household size.” BMJ: British Medical Journal 299, no. 6710 (1989): 1259.
3. Derraik, José GB, Fredrik Ahlsson, Maria Lundgren, Björn Jonsson, and Wayne S. Cutfield. “First-borns have greater BMI and are more likely to be overweight or obese: a study of sibling pairs among 26 812 Swedish women.” Journal of epidemiology and community health (2015): jech-2014.
4. Kragh, M., Jeppe Madura Larsen, Anna Hammerich Thysen, Morten Arendt Rasmussen, Helene Mygind Wolsk, Hans Bisgaard, and Susanne Brix. “Divergent response profile in activated cord blood T cells from first‐born child implies birth‐order‐associated in utero immune programming.” Allergy 71, no. 3 (2016): 323-332.
5. Ayyavoo, Ahila, Tim Savage, Jose GB Derraik, Paul L. Hofman, and Wayne S. Cutfield. “First-born children have reduced insulin sensitivity and higher daytime blood pressure compared to later-born children.” The Journal of Clinical Endocrinology & Metabolism 98, no. 3 (2013): 1248-1253.

Disclaimer: The content is purely informative and educational in nature and should not be construed as medical advice. Please use the content only in consultation with an appropriate certified medical or healthcare professional.

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