In coronary heart disease
the walls of the arteries supplying blood to the muscle of his heart
become hardened, and the channels within them narrowed by deposits of
fats. The risk of heart disease is higher in people who had low birthweight.
Risk falls progressively across the range of birth weights. People who
weighed 7-pound at birth are at lower risk than those who weighed
6-pounds. People who were 9-pound babies are at lower risk than those
who were 8 pounds. Studies in the US, in other European countries and in
India have confirmed the first observation of the link between heart
disease and birthweight, which was made in the UK. It is not babies who
were small because they were born prematurely who are at increased risk
of later heart disease, but babies who were small because they grew
slowly.
Until recently it was thought that the heart was
never sacrificed during life in the womb. Like the brain it is essential
for survival and is protected, though there must come a point beyond
which protection is no longer possible. In the womb, as the heart pumps
blood through the blood vessels in the placenta the pressures against
which it has to work shape the thickness of its muscular walls and the
size of its chambers for life. The mother’s nutrition shapes the
placenta; and the placenta shapes the baby’s heart.
At birth the heart is almost complete; its muscle cells
are mostly mature and it needs only to enlarge as the body grows. Before
birth it is sensitive to the environment. If it is undernourished it
can speed up its maturation, perhaps in preparation for an early birth.
This, however, leaves it with a smaller number of muscle cells, a
diminished reserve for repair in later life. Another response,
discovered only recently, is for the heart to slow its growth. But this
too limits its reserve. Many babies are born with hearts that will be
vulnerable to disease in later life.
Cholesterol is important because the body uses it to
build the walls that enclose its cells. Most of the cholesterol in the
body is not eaten in food but is made in the liver which controls how
much cholesterol there is in the blood. A tape measure placed around the
stomach of a newborn baby measures the size of its liver because, until
it begins to feed, its intestines are mostly empty. There are large
differences in the girth of the stomachs of newborn babies. This
reflects differences in overall body size, but also the extent to which
babies have traded off liver growth to protect brain growth. Remarkably,
the girth of the stomach of newborn babies has been found to predict
their blood cholesterol levels sixty and more years later. The greater
the girth, the lower the cholesterol. We have become accustomed to the
idea that high blood cholesterol, and the increased risk of heart
disease linked to it, is evidence of an unhealthy diet. The truth may be
that it is evidence of poor liver growth in the womb. In animals it is
easy to change the activities of the liver permanently by altering the
mother’s diet in pregnancy. This happens because undernutrition changes
the balance of the liver’s specialist cells.
