Eldest children have taken a knock in the sibling rivalry stakes.
The first-born is at greater risk of diabetes and high blood pressure, according to a new study from Auckland University's Liggins Institute.
Researchers found the eldest child has greater difficult absorbing sugars, which increased the risk of type 2 diabetes.
Added to this, the first-born was also more likely to have higher blood pressure compared to their younger siblings.
However, scoring some points against their siblings, the study revealed the eldest child was slimmer and on average 3cm taller than their young counterparts.
Professor Wayne Cutfield, who co-wrote the paper, said being the first born does not necessarily predict conditions like heart disease, stroke or diabetes, but it can contribute to the overall risk.
"Our results indicate first-born children have these risk factors, but more research is needed to determine how that translates into adult cases of diabetes, hypertension and other conditions."
Researchers say changes in the mother's uterus during her first pregnancy might cause the differences between siblings.
These changes lead to an increased flow of nutrients to the baby in subsequent pregnancies.
The findings could have wider repercussions for the public health system.
A larger proportion of populations are expected to be made up of first-born children due to shrinking family units.
This could lead to increasing rates of the population developing conditions like type 2 diabetes, coronary artery disease, stroke and hypertension.
Researchers say this could put pressure on health systems in nations like China, where a one-child policy has led to a large part of the population being first-born children.
The Liggins Institute study looked at 85 healthy children and found the 32 first-born children had higher blood pressure and risk of diabetes.
Research found a 21 percent drop in insulin sensitivity among first-born children.
The research is due to appear in the March issue of the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.