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There are a host of things that can influence your risk of developing a disease, from genetics to environmental exposures to lifestyle factors. But new research suggests there\u2019s one more that probably isn\u2019t on your radar: your place in your family\u2019s birth order.<\/p>\n
The study, published in Nature Health<\/a>, analyzed health data from more than five million two-child families\u2014and found a clear link between an individual\u2019s birth order and how likely they were to develop certain diseases. While first-borns in the study had a higher risk of neurodevelopmental conditions like ADHD and immune-allergic diseases like food allergies, second-borns were at greater risk for gastrointestinal disorders and substance abuse disorders. Another interesting finding: A shorter gap between siblings\u2019 ages seemed to protect against neuropsychiatric and allergic conditions.<\/p>\n Andrey Rzhetsky, Ph.D<\/a>., study co-author and professor of medicine at The University of Chicago Biological Sciences Division, says he decided to do the study after observing several families in which older and younger siblings had different health issues and temperaments.<\/p>\n While Rzhetsky\u2019s study didn\u2019t explore why these differences exist, doctors say there could be something here. Below, experts break it down.<\/p>\n Meet the experts<\/strong>: Andrey Rzhetsky, Ph.D<\/a>., study co-author and professor of medicine at The University of Chicago Biological Sciences Division; Mark Hicar, M.D., Ph.D<\/a>., chief of pediatric infectious diseases at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences; Danelle Fisher, M.D<\/a>., pediatrician at Providence Saint John\u2019s Health Center; Ashanti Woods, M.D.<\/a>, pediatrician at Mercy Medical Center.<\/p>\n What disease risks does birth order carry?<\/strong><\/p>\n The study compared each child\u2019s odds of being diagnosed with a disease against their sibling\u2019s odds of developing the same disease. After crunching the data, the researchers found that first-borns and second-borns did have relatively higher odds of developing some conditions.<\/p>\n What the data showed for first-borns:<\/p>\n What the data showed for second-borns:<\/p>\n Add Prevention as a preferred source in your Google search results.<\/p>\n Use your Google account to add this to your settings.<\/p>\n Add to Google settings<\/p>\n What\u2019s behind this?<\/strong><\/p>\n The study didn\u2019t look at why birth order affected the risk of developing some diseases. However, there are a few theories.<\/p>\n \u201cIt is possible there is something inherent to the order,\u201d says Mark Hicar, M.D., Ph.D<\/a>., chief of pediatric infectious diseases at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences in Buffalo, New York. \u201cThere are biological differences between the first pregnancy and subsequent pregnancies, including age, changes to mom\u2019s body, and differences in immune responses.\u201d Each baby technically contains foreign material from the father that the mother\u2019s immune system must become tolerant to, which \u201chas been shown to improve with subsequent pregnancies,\u201d Dr. Hicar adds.<\/p>\n Rzhetsky points out that siblings also tend to share a microbiome. \u201cThis could explain signals in infectious diseases, allergies, and the potential protective effect of a small age gap for neurodevelopmental conditions,\u201d he says.<\/p>\n It also could have something to do with parental behavior. First-time parents may be more likely to escalate a concern to a healthcare provider, prompting an evaluation and diagnosis, compared to when they have more children, Rzhetsky says. The parents\u2019 age may matter, too. \u201cStructurally, birth order correlates with parental age at birth, meaning first-borns inherently have younger parents,\u201d he says.<\/p>\n Dr. Hicar agrees that how parents treat first-borns and second-borns may have an effect. \u201cIf your first-born has a neurological condition, you may get more testing with subsequent pregnancies,\u201d he says. \u201cAnother example is that planned environmental and dietary exposures tend to be stricter with first-borns than later pregnancies as well.\u201d<\/p>\n\n
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