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What Is the Best Measure of Health?

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A decade ago, my wife worked as a research assistant for a researcher studying obesity. The research team met once a week to brainstorm ideas. They were planning a study to test the urban myth that the average college student puts on 15 pounds during their first year away from home.

The study was nearly ready to go when my wife asked a simple question: "I might be missing something, but why are we ignoring the summer between the end of high school and start of college? A number of kids probably gain weight while they are partying their asses off before classes begin." Everyone in the meeting turned to my wife in astonishment: "Of course, brilliant! You saved the study."

So what's the lesson from this? Scientists have to spend time out of their heads and inside the real world. One of many reasons, I turn to my wife to shoot holes in my ideas.

Everyone gets excited about scientific studies with unusual, expensive measures of physical health: Natural Killer T cells counts when confronted by life stressors (a marker of immunological functioning), greater activity in the the left compared to the right dorsolateral prefrontal cortex (a marker of tendencies to approach the world in search of rewards instead of withdrawing from the world to avoid threat).

But what is the best marker of physical health? What is the best way to tell whether a person reached their genetic potential?

The answer is simple, obvious and neglected: height. As a child grows in physical stature, we know that the rest of them is growing and maturing as well. As our children get taller, we know that their brain is growing and maturing. This is good. If you look across the past few centuries, you will find that the average height of men and women has systematically increased. If you look at countries where there has been continual poverty, a lack of nutritious food and unsanitary conditions, you can find stagnation or even declining height in the population. Height, a simple metric, is a powerful gauge of economic progress.

In Britain and the United States people's height at age three is strongly related to height in adulthood -- correlations are greater than .70 for both men and women. Also, height is strongly linked to scores on tests of intelligence or executive functioning. Thus, height offers a portal to physical health, a window into whether someone missed reaching their genetic potential. Height is an excellent marker of what happened during development, whether it is the nutrition received or mental and physical health during childhood and adolescence.

Like every measure of health or well-being, height is an imperfect measure. And if you are going to use height as a gauge of genetic potential then obviously you must account for the genetic contributions of parents -- and even grandparents -- in terms of their height.

As parents, we want our children to have an opportunity to reach their potential. As scientists, sometimes it is useful to forgo complexity for accuracy and simplicity. If we want to raise the well-being of people around the globe, let's not forget the basics of dealing with prenatal maternal stress, nutritious meals and clean water. Psychology cannot be divorced from biology. Changes in height, from one generation to the next, will offer a hint of whether we are moving in the right direction with our interventions.

Dr. Todd B. Kashdan is a clinical psychologist and professor of psychology at George Mason University. He is the author of "Curious? Discover the Missing Ingredient to a Fulfilling Life" His new book Designing Positive Psychology can be pre-ordered. For more about his speaking engagements, books, and research, go to www.toddkashdan.com or Research Laboratory.