Human height may have peaked in the U.S.; should we be worried?

Our society puts quite a premium on height: Tall people earn more money, are often perceived as more attractive and get better views at crowded concerts. So new research suggesting that we may have reached peak height feels a bit unsettling.

The study in question compiled data from more than 1,000 papers stretching back to 1896. Analysis revealed that in many countries — including the United States, Britain and Japan — the trend of steadily increasing height has either slowed substantially or plateaued altogether. In other words, in some of these places, we may have reached peak height.

In the United States, peak height for women seems to have happened in 1988, when women maxed out at an average of 5-foot-4.4. American men peaked slightly later, in 1996, at 5-foot-9.5.

Is it all downhill from here?

For Americans, average heights these days are only lower by between 0.01 and 0.05 centimeters, a negligible difference. And plenty of places are still getting taller — for example, many countries, particularly in Latin America, are still seeing an upward trend in height and one that is increasing at a quicker rate in recent years. (Of course, these people are still shorter than we are on average, even though they're catching up.)

Exactly what that upper height limit is appears to vary among countries. Different nationalities, even ones that seem to have peaked, do so at different heights. For example, while the men of Scandinavian countries appear to be approaching an average height just north of 180 centimeters (a shade under 5-foot-11), Japan's men topped out nearly 10 centimeters (nearly 4 inches) below that, despite plateauing in the 1960s, among the earliest of any country in the study.

So what explains the differences? At the population scale, average heights have likely been increasing thanks to nongenetic environmental factors, like maternal size, nutrition and access to health care. It is therefore not terribly surprising that the world map of heights seems to correlate pretty closely with gross domestic product — higher income increases access to better food and quality health care, which in turn makes a population healthier and eventually, taller.

What these findings indicate, in part, is that there may be a convergence point, a limit in human height under these preferable conditions — a biological asymptote.

It is a bit strange that the authors of the paper suggest that the slowing of our height rate is a public health crisis in and of itself. "Being taller is associated with enhanced longevity, lower risk of adverse pregnancy outcomes and cardiovascular and respiratory diseases," write the authors. That association may be true, but it doesn't mean one is causing the other.

Exponential growth in height would not, for example, lead to exponentially lower risk of cardiovascular disease. It's telling that the authors do not suggest any public policy changes to correct our supposed height crisis. The slowing of growth is not actually a crisis, because it's not causing the problems that are correlated with shorter height. Instead, there's a third factor at play — overall health — that, when good, contributes both to increased height and improved health outcomes.

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For example, elsewhere in the paper, the authors write: "These gains (in height) may partially account for the fact that women in Japan and South Korea have achieved the first- and fourth-highest life expectancy in the world." But women in these countries are long-lived not because they've gotten taller. They're likely long-lived for the same reason they're taller, which is that they're healthier overall.

At any rate, when it comes to the social benefits of height — be it higher salary or a better view — whether you're tall or not is relative. Even if we're at or past peak, there will still be a divide along which taller people can celebrate and shorter people can lament.

© 2016 Slate