Healthy(?), wealthy, and wise: Birth order and adult health

- Previous research has shown that birth order affects education, IQ scores, and earnings.
- We explore the effects of birth order on adult health.
- Beneficial effects of being later-born are found for obesity and blood pressure.
- We find adverse effects of later-birth for smoking and self-reported physical and mental health.
- Some health-related early childhood investments by mothers favor first-borns.

While recent research has found that birth order affects outcomes such as education and earnings, the evidence for effects on health is more limited. This paper uses a large Norwegian dataset to focus on the relationship between birth order and a range of health and health-related behaviors, outcomes not previously available in datasets of this magnitude. Interestingly, we find complicated effects of birth order. First-borns are more likely to be overweight, to be obese, and to have high blood pressure and high triglycerides. For example, compared to fifth-borns, first-borns are about 5% points more likely to be obese and 7% points more likely to have high blood pressure. So, unlike education or earnings, there is no clear first-born advantage in health. However, first-borns are about 13% points less likely to smoke daily than fifth-borns and are more likely to report good physical and mental health. Later-borns also score lower on well-being with fifth-borns being about 9% points less likely than first-borns to report that they are happy. Our findings are generally monotonic with middle-borns having outcomes that are intermediate between first- and fifth-borns. We find that these effects are largely unaffected by conditioning on education and earnings, suggesting that these are not the only important pathways to health differentials by birth order. When we explore possible mechanisms, we find that early maternal investment may play a role in birth order effects on health.