Firstborn girls are more
likely to be
overweight or
obese in comparison to their youngest sisters, new research suggests.
The study, published in the Journal of Epidemiology and
Community Health, set out to determine whether birth order influenced a woman’s
height and weight in early life and adulthood.
Previous studies involving men found that firstborn sons are
more likely to be taller and are at a greater risk for obesity, but data on
whether a similar pattern exists in women is lacking.
Because of this, Professor Wayne Cutfield, of the University
of Auckland in New Zealand, and his research team, felt that this area of
research needed to be addressed.
"This is the fourth study we have done to characterize
the health risks of firstborn in four different populations,” he said.
"If you look at
the health risks of those that are firstborn, you find that firstborns are more
insulin resistant than later borns, which is a risk factor for diabetes, and
they have higher blood pressure than later borns.”
Using data from the Swedish Birth Register, the research
team analyzed 303,301 women who were born between 1973 and 1988 who gave birth
between 1991 and 2009. 206,510 of the women were firstborn or secondborn.
Of the 206,510, researchers identified 13,406 pairs of
sisters, and assessed their weight and height at birth and at their first
prenatal visit when they had reached the third month of their pregnancy.
The study found that firstborn sisters tended to weigh less
at birth as compared to their younger sisters. However, their body mass index
(BMI) was 2.4% higher during their first 3 months of pregnancy.
The results concluded that firstborn sisters were 29% more
likely to be overweight and 40% more likely to be obese than their younger
sisters.
"Our study
corroborates other large studies on men, as we showed that firstborn women have
greater BMI and are more likely to be overweight or obese than their secondborn
sisters."
Although the cause for this phenomenon is unknown, Curfield
thinks that it may be because of more narrow blood vessels. In a woman’s first
pregnancy, the blood vessels are narrower causing less blood to reach the
placenta.
The researchers also made a possible connection to the lower
birth weight in firstborns and the fact that firstborns are more susceptible to
receive less than optimal nutrition in the womb.
"And this
information has led to the hypothesis that firstborns were exposed to in utero
compromise, which reprograms metabolism and the regulation of fat."
Curtis feels as though his research could help empower
firstborns to make healthier decisions throughout their lives, decisions that
could reduce the risk of high blood pressure, obesity, and diabetes.
"There are minor
health risks associated with being firstborn. I don't want firstborns to think
they will become obese or get diabetes or high blood pressure -- it is a risk
factor, and the risk of getting a disease is a combination of risk factors, not
just a single risk factor."
The study suggest that future studies with a large amount of
subjects should research whether metabolic health issues are more prevalent in
firstborn adults women.
This is not the first time birth order has been determined
to affect certain characteristics in individuals.
A psychologist who has been studying birth order since 1967,
says: "The one thing you can bet your paycheck on is the firstborn and
secondborn in any given family are going to be different."
A small study from New Zealand discovered that firstborns
are at higher risk of developing heart disease and diabetes.
Firstborns often tend to be more rebellious, conscientious,
structured, cautious, and controlling than their younger siblings. They have
also been found to be the highest achievers in the family.
This personality is based on family dynamic and not
pre-natal conditions. Because of the mass amount of control and attention given
to them by their parents, they become over-responsible, well-behaved, smaller
versions of their first-time parents.
Research has also found that firstborn children not only
tend to have higher I.Q.'s than their younger siblings, but are also more
likely to be the most ambitious and well-qualified of all the siblings. Their
younger siblings tend to excel more in sports or the arts.
Firstborns also tend to be more conservative than their
secondborn siblings. Research suggests these differences also stem from the
family dynamic.
