The New York Times Health section has a really well-written article about recent secular trends in longevity and body size, by Gina Kolata.
The article's point of departure is the health records of Civil War veterans. Of course, these have the shock value of describing terrible health problems that people don't even hear about anymore (the article mentions grapefruit-sized chronic hernias, and "dropsy"). But beneath these fairly startling differences, there is a huge statistical difference in death rates at ages that we today consider surprisingly young to die.
These people's genes were the same as people today, more or less. So the health differences are mostly due to our new environment. In particular, all those vaccinations, vitamins, and antibiotics really have made people bigger and healthier:
At a recent meeting of a Las Vegas chapter of the Sons of Confederate Veterans, eight burly men crowded into a library meeting room. All had experienced the equivalent of the Civil War tent problem.
"At the re-enactments, all the directors, all the costume directors say the re-enactors are just too darn big," said George McClendon, a hefty 67-year-old retired airline pilot.
Mr. McClendon is right. Men living in the Civil War era had an average height of 5-foot-7 and weighed an average of 147 pounds. That translates into a body mass index of 23, well within the range deemed "normal." Today, men average 5-foot-9½ and weigh an average of 191 pounds, giving them an average body mass index of 28.2, overweight and edging toward obesity.
You may be wondering, this is supposed to be better? Well, yes, at least when it comes to long-term health -- the Civil War veterans as a class were healthier and longer-lived in positive relation with body size. And diseases early in life (that themselves could stunt growth) caused problems later in life also:
"Suppose you were a survivor of typhoid or tuberculosis," Dr. Fogel said. "What would that do to aging?" It turned out, he said, that the number of chronic illnesses at age 50 was much higher in that group. "Something is being undermined," he said. "Even the cancer rates were higher. Ye gods. We never would have suspected that."
Men who had respiratory infections or measles tended to develop chronic lung disease decades later. Malaria often led to arthritis. Men who survived rheumatic fever later developed diseased heart valves.
Nor is it only effects during childhood or early adulthood. There seem to be prenatal effects as well:
So did a study of babies born to women who were pregnant during the Dutch famine, known as the Hunger Winter, in World War II.
That famine lasted from November 1944 until May 1945. Women were eating as little as 400 to 800 calories a day, and a sixth of their babies died before birth or shortly afterward. But those who survived seemed fine, says Tessa J. Roseboom, an epidemiologist at the University of Amsterdam, who studied 2,254 people born at one Dutch hospital before, during and after the famine. Even their birth weights were normal.
But now those babies are reaching late middle age, and they are starting to get chronic diseases at a much higher rate than normal, Dr. Roseboom is finding. Their heart disease rate is almost triple that of people born before or after the famine. They have more diabetes. They have more kidney disease.
It's a good article, and I think it makes a good stepping-off point for talking about the relationships of epigenetics and environment in the determination of disease risks. The one thing that we still know relatively little about is the extent to which late-life chronic diseases relate to different genotypes, and we will certainly be learning a lot more about that soon.
In essence, human genes respond to a history of relatively high early-life disease and high late-life mortality. We've gone and mucked up that killer environment, to our great advantage. Isn't it interesting, then, that these genes are capable of making bigger, healthier people when their environment has gone. After all, it didn't have to be that way.
And apparently it sometimes isn't that way. At least, it seems that those immune system genes that used to fight early childhood diseases now may be causing auto-immune disorders since they no longer have diseases to fight.
So we may be looking at a particular axis of disease and growth here, involving body size, status, nutrition, stress, cardiovascular health, and dementia. Which sure takes in a lot.