When a pregnant woman doesn't take care of herself, you might expect her baby to suffer from birth defects or childhood illnesses. But what happens when her baby grows up? In this Science Update, you'll hear about a recent study that suggests that malnutrition in the womb can come back to haunt you well into adulthood.
Tracing strokes back to the cradle. I'm Bob Hirshon and this is Science Update.
Babies who are born underweight or premature may face a higher risk of stroke decades later. That's according to Daniel Lackland, a professor at the Medical University of South Carolina.
He was studying an area of the southeastern United States called the stroke belt. Stroke rates are higher there, and factors like diet, obesity, and disease couldn't fully account for the difference. So Lackland compared notes with British researcher David Barker, who was studying a similar area in northern England.
He found that areas that had high stroke rates also had areas of high infant mortality, they also had high rates of low birth weight. And if we then look and see almost that exact type of pattern that you see in the Southeast.
They also found that underweight babies were more likely to have strokes as adults, even if they left the area. Lackland says that adding other risk factors can worsen the outlook.
An individual that's a low birth weight baby that then becomes an obese adolescent or an obese teenager is going to be even at a greater increased risk, and that seems to be playing a role too.
He says the study shows that poor nutrition in the womb can have effects that linger for life. For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
This study is a good example of an epidemiological detective story. It starts with a long-observed trend: in an area of the American Southeast, from the Virginia-North Carolina state border down into Georgia, stroke rates are higher than in the rest of the country. It was first noticed in the 1920s and persists today. The pattern was so pronounced that doctors started calling it the "stroke belt."
Ever since the stroke belt was identified, scientists have tried to explain it. But they keep coming up short. People in this region do have slightly unhealthier diets and fairly high obesity rates compared to other areas, but those risk factors alone can't fully explain the difference. Something else had to be common to residents of this area. But what?
It turns out that other countries have stroke belts too. In England, the stroke belt is in the northern, industrial areas—a very different climate and culture from the American South. When they compared notes, Lackland and his English collaborators found that both stroke belts had high rates of infant mortality and low birth weight. Could there be a connection?
To explore this possibility, they asked themselves what common cause might give rise to low birth weight and infant mortality. The nutrition of the mother seemed like a good candidate, especially since it's something that could be heavily influenced by cultural and economic conditions. Next, they looked at people born at low weights (below 5 ½ pounds), and followed them into adulthood. They noticed that indeed, people who were born underweight were more likely to have strokes decades later. This was true regardless of the socioeconomic class they ended up in as adults: in other words, it wasn't just because people who were born to low-income or malnourished mothers tended to be low-income or malnourished themselves. The risks associated with low birth weight appear to follow you wherever you go.
The mystery, of course, is far from solved. Lackland and his colleagues have shed light on the nature of the stroke risk, but they haven't proven that maternal malnutrition is the cause. And while it's known that poor nutrition in the womb can lead to low birth weight, it's not at all clear how this could lead to a higher stroke risk later in life. Lackland has a few ideas: he notes that babies born underweight have less fully developed kidneys—and some of this underdevelopment can't be corrected after birth. So it's possible that adults who were born premature are prone to overloading their kidneys. Kidneys regulate blood pressure, which in turn affects the risk for stroke.
Another possible mechanism lies in the blood vessels. Babies born prematurely have less of a substance called elastin, which makes their veins and arteries flexible. Stiffer arteries mean higher blood pressure, which may again contribute to stroke many years down the line.
It's also important to note that even if these theories prove correct, they're only one small part of the picture of stroke risk. Underweight babies are by no means inevitably doomed to strokes, nor are healthy babies exempt from the risk. But if Lackland's suspicions prove correct, it would add one more reason for mothers to watch their health especially closely during pregnancy.
Now try and answer these questions:
- What is the "stroke belt?" What is its connection to maternal nutrition?
- What does Lackland's research show? What does it leave unanswered?
- If Lackland's theory were true, what else would you expect to be true? Can you think of an experiment or study that might further test his theory?
- Would it ever be possible to prove that poor maternal nutrition actually causes a higher risk of stroke? Why or why not? Is it important to do so?