HOW OUR LIVES ARE SHAPED BY OUR TIME IN THE WOMB

Saturday, July 26, 2003

Genes or environment? When it comes to health, it's not just one or the other that determines whether you're sick or well; it's also what the environment does to determine how your genes work. And the environment a baby experiences before birth does a lot of the determining.

That's the premise of a medical research field called ``fetal origins of adult disease,'' not a new field exactly but the subject of increasing interest as progress in genetics allows researchers to tease out the intricate interplay between nature and nurture. The Economist magazine recently reported on a major conference devoted to the subject, held in Brighton, England, in June.

A poorly nourished fetus may, unsurprisingly, be born smaller than usual, but there may also be metabolic differences that don't manifest their harmful effects until later in life. ``A fetus takes its cue about what it will eat after it is weaned from its mother's physiology,'' the Economist writer says, ``and adapts accordingly.''

It's hard to write about this without slipping into language that suggests intention, but that's not the meaning at all. All that is going on is biochemical signaling that flips some genes on and others off, so the baby comes into the world predisposed to be either one of those lucky people who can eat anything and never gain an ounce -- or, on the unlucky end, a couch potato.

It's the children of food-deprived mothers who are more likely to get the couch-potato syndrome, because they are the ones whose environment signals ``lean times ahead.'' In animal experiments done by Mark Vickers of Auckland University, undersized rat pups whose mothers are ill-nourished eat more and are less active than normal-weight offspring of well fed mothers.

Observations suggest that much the same thing happens in humans, and fanatical dieters probably ought to be thinking about it if they are contemplating pregnancy. Not long ago I heard a nutritionist with a consulting practice say that she really worries when some of her patients who are strict vegans on very-low-fat diets get pregnant.

This line of research began, in The Economist's summary, with a study by Dr. David Barker, of the University of Southampton, who observed that very small babies have an increased risk of heart disease as adults. In 1988, Gerald Reaven of Stanford University identified a cluster of symptoms associated with low birth weight, including high blood pressure, altered fat metabolism, obesity and, consequently, adult-onset diabetes as well as heart disease.

That's already not good news, though it may have made perfect evolutionary sense in a time when famine was much more likely than feast. Mark Hanson, of Southampton, and Peter Gluckman, of Auckland, point out that a biological mechanism allowing individuals to adapt to short-term changes in the availability of nutrition -- even if they only get to do it once in a lifetime -- is a far better survival tool than anything the slow process of natural selection can offer. Children better adapted to life in times of scarcity had a better chance to survive to have children of their own, and the fact that they might begin to develop high blood pressure at the age of 50 -- as demonstrated in a Swedish study -- was of comparatively little importance when the average lifespan was 25.

But when a baby pre-adapted to life in a low-fat, low-calorie environment grows up in a high-calorie, high-fat world, the bad effects are multiplied. Hanson and Gluckman describe the process of storing fat as the human equivalent of the camel's hump. But humans don't need humps, and obesity, especially when it results from excess weight gain in childhood, is a strong predictor of future medical problems.

Not all the research is discouraging. Some suggests that better fetal nutrition can reduce health problems later in life. According to The Economist, one study of premature babies found that those who received nutritionally enriched formula for a month after birth (that is, during the normal term of the pregnancy) were, by their midteens, noticeably smarter -- especially in math -- than those who received only a standard formula. Dietary supplements, if properly balanced, help to increase birth weights.

And finally, The Economist points out, exercise helps prevent diabetes even if the person exercising doesn't lose weight, because it alters the way the body responds to insulin. Unfortunately, that advice is hardest to follow precisely for the people who need it most.