FORGET poverty, poor job prospects and stress. When it comes to suffering a
heart attack in later life, being small at birth is a more important risk
factor.
These findings, published in the 30 November issue of the The Lancet
(vol 348, p 1478), support a controversial theory of heart disease proposed by
epidemiologist David Barker of the University of Southampton. Surprisingly the
paper comes from researchers who have been among Barker鈥檚 toughest critics.
Since the late 1980s, Barker and his Southampton colleagues have argued that
undernourishment in the uterus can permanently 鈥渞eset鈥� the physiology of a fetus
so that it is more vulnerable to heart disease in later life (see 鈥淥ff to a bad
start鈥�, 快猫短视频, 8 June 1996, p 41).
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George Davey Smith of the University of Bristol was not convinced. 鈥淚 thought
small babies were just born into a disadvantaged world鈥攖hey鈥檇 get less
education, worse jobs, and they鈥檇 smoke more,鈥� he says. Now he has changed his
mind. 鈥淲hen we analysed our data, we could not get rid of the effect of low
birth weight. There鈥檚 clearly something important going on.鈥�
Davey Smith, Stephen Frankel and others at Bristol, with their colleagues at
the Medical Research Council鈥檚 Epidemiology Unit at Llandough Hospital in
Penarth, Wales, and at Queen鈥檚 University, Belfast, spent 10 years monitoring
more than 1200 men in Caerphilly, Wales, aged between 45 and 59 whose birth
weights had been recorded. They found heart disease was much more common in the
men with low birth weight. Conventional risk factors for heart
disease鈥攕uch as lower social class, blood cholesterol levels, blood
pressure or even smoking 鈥攃ould not explain away the effect of low birth
weight.
But the team did find that people who were born small and then grew fat in
middle age had the strongest risk of heart disease. Resetting the body鈥檚
physiology a second time by becoming obese, they argue, may increase the risk of
heart attack. Small babies who stayed slim as adults did not seem to be any more
susceptible than those of normal birth weight.
Barker accepts the main finding of the study, but not the idea that
later obesity is what harms underweight babies. His team鈥檚 own investigation of
heart disease in South India found no difference in body mass between those with
heart disease and those without. The group with the highest rate of heart
disease had weighed 2.5 kilograms or less at birth, and the group with the
lowest rate had weighed 3.1 kilograms or more at birth, irrespective of adult
weight. The people whose mothers were underweight during pregnancy also had an
increased risk. 鈥淗eart disease in India is not about poor, impoverished men
becoming fat,鈥� he says.
Researchers have known for a while that babies who are thin at
birth face an increased risk of developing diabetes and having high blood
pressure鈥攂oth clear risk factors for heart disease. And pregnant rats fed
a low-protein diet give birth to pups with high blood pressure. But Barker
suspects that these risk factors are really just secondary consequences of a
more general shift in metabolism caused by fetal undernourishment.