Why is everyone else getting taller?
A paper (free full text) in this month’s Social Science Quarterly points out an interesting but not entirely unexpected phenomenon: people in the rest of the world are growing taller than those of us in the United States.
It seems remarkable that this could happen because over the past couple of centuries people in the United States were significantly taller than their European counterparts. Suddenly, starting in the 1950s, people in the US quit growing. They didn’t get shorter; they simply quit growing larger. For years, just as there has been an improvement in longevity in this country, there has been an ever increasing increase in average height. Then, in about 1950 it stopped. People born in the years 1955-1974 for the first time were no taller than those born the years previous to that. People born in the rest of the Western world during those years raced past us and now surpass in average height those Americans born between 1955 and 1974.
What has happened? Why the steady gains in stature for two centuries, then a reversal? Why does the rest of the world continue to grow?
Good questions all. The answers, I suppose, depend upon whom you ask.
If you ask the researchers that wrote this paper, you’ll get one answer. If you ask me, you’ll get another.
The people who wrote the paper are sociologists. I’m a physician grounded in biochemistry and physiology. Let’s see how our answers differ.
First, though, just to give you an idea so that you can start thinking ahead…remember back when you were in school and all the people you knew were separating out into their different majors. Some went into engineering, others into science, others went into history, literature or the arts, and some went into sociology. Remember the ones who went into sociology? Well, those are the people who became sociologists, so that explains a lot.
After going through all the statistics to show that there really is a growing discrepancy between the average heights of Americans and the average heights of Europeans – which I have no problem accepting – the authors speculate on the cause of this difference.
They first make a nod toward nutrition:
Why U.S. heights declined in relative terms remains a conundrum, a topic for future research, but even at this stage of our knowledge we can conjecture that there are differences in the diet of U.S. and European children that could affect human growth. For example, U.S. children consume more meals prepared outside the home, more fast food rich in fat, high in energy density, and low in essential micronutrients, than do European children.
Then they launch into what I consider lunacy:
Moreover, consideration of the differences in the socioeconomic institutions of Europe and the United States might help in at least beginning to resolve this paradox. Without claiming to propose a comprehensive answer to this quandary, we propose the hypothesis that there are several crucial differences between the western and northern European welfare states and the more market-oriented economy of the United States that might well shed further insights into this paradox. This includes greater socioeconomic inequality and more extensive poverty in the United States. European welfare states provide a more comprehensive social safety net, including universal health-care coverage, while the share of those who have no health insurance in the United States is about 15 percent of the population. Is it possible that the western European welfare states are able to provide better healthcare to children and youth than the more market-oriented U.S. one? Or is there something about the quality of healthcare that is responsible for these results?
It should be real easy to determine whether the above sociological jibberish holds any merit: simply compare wealthy Americans (all of whom presumably have decent healthcare) to wealthy Europeans and poor Americans (who presumably have bad healthcare) to poor Europeans (who supposedly have the same health care as the wealthy). If the wealthy Americans and Europeans are the same height and the poor Americans are shorter than the poor Europeans, then we could maybe make a case for a difference in health care. If both rich and poor Europeans are taller than their American counterparts, then it’s tough to make a case for a healthcare difference causing the problem.
The authors do look at this. And what do they find?
The lagging U.S. height performance is not caused by a long left tail in the height distribution. Heights are normally distributed and the whole U.S. height distribution is shifted to the left. In other words, rich Americans are shorter than rich western Europeans and poor white Americans are shorter than poor western Europeans.
Case closed. Or as Samuel Johnson would have said, “There’s an end on’t.” It ain’t a difference in the healthcare system.
So, what is it?
I would say it is the massive amounts of soft drinks that American kids drink compared to their European counterparts. That huge upswing in soft drink consumption in the U.S. started post WWII and has increased since.
How would soft drinks make us shorter?
It’s a little complex, but let’s tackle the physiology.
First, puberty and growth are stimulated by sex hormones and IGF-1 (insulin-like Growth Factor). These hormones are in two forms: the free form and the bound form. The free form is when the hormone is off doing its hormone-y thing. The bound form is when the hormone is bound to its binding globulin. Both hormones circulate in the blood in both ways: bound and free. When you get a blood test, it measures the total, i.e., both free and bound. If you want to see what the actual active hormone is doing, you’ve got to get a Free Testosterone or a Free IGf-1.
The binding globulins for these hormones are made in the liver. If the liver cranks out a lot of binding globulin, then a lot of the hormone will be bound and not be active. If the liver does the opposite and produces little binding hormone, then the amount of hormone bound will be less and there will be more active hormone out doing its thing.
Elevated levels of insulin drive the liver to make LESS binding globulin, which means that there will be MORE of the free and, therefore, active hormone available. More IGF-1 leads to acne, nearsightedness, and an early growth spurt. More free sex hormone leads to an earlier puberty and closure of the growth plates. (the growth plates are at the ends of the bones, and when the growth plates close, the bone quits growing in length. When long bones stop growing, you stop getting taller.)
What make the levels of insulin go up? We all know the answer: carbs. Especially refined carbs. Especially sugar. Even worse is fructose because fructose adversely affects the liver without raising insulin levels.
What are soft drinks? Sugar water. Sugar water now made with high-fructose corn syrup (HFCS). Both sugar and HFCS contain glucose which raises insulin and fructose which makes the insulin even more harmful to the liver and enhances the liver’s insulin resistance.
An insulin resistant liver makes less binding globulin, less binding globulin allows more free hormone, more free hormone hastens puberty and stops growth. Voila! A much more sensible explanation than that concocted by our sociologist friends in the above paper. And one grounded in science, not a we-should-have-socialized-medicine twisting of the facts.
There is another viewpoint on this. When I read this paper, I emailed by bud Loren Cordain to see what he thought of it. He has a different theory than I do on the actual physiological cause, but, as he sees it, the underlying problem is the same.
Here is an excerpt from his email to me (reproduced with his permission):
After attending the Harvard conference on milk drinking & sitting through the Brit’s presentation of a famous longitudinal trial on milk drinking and stature conducted in the 1930’s and resurrected in the present with still living members, my feelings are that increased milk consumption probably is the most important dietary determinant of adult stature. The two underlying mechanisms: BTC in milk binds human luminal gut EGF-R and ends up in circulation and thereby binds 3 of the 6 EGF-R dimers in chondrocytes, thereby promoting skeletal growth during development; secondly the (protein + lactose) in milk facilitates insulin resistance which increases IGF-1 and further adds to milk’s growth promotional effects during adolescence. The probable reason Europeans are surpassing Americans in stature is because they continue to have high milk consumption while US teens have replaced milk with soft drinks. BTC + lactose is more powerful than sucrose alone in promoting increased stature.
I like my rationale better, but we are both in agreement that the root cause of the decrease in stature is the increased consumption of soft drinks during the childhood and teenage years.
They’re poison. Don’t let your kids drink them.