by Wei Perng, PhD
Social inequality & poverty. Komlos speculated that the shrinking height of Americans could be attributable to social inequalities. We typically see a direct relationship between a country’s per capita income and height of its people. Yet, according to our gross domestic product (GDP), which is higher than that of any other major economy, Americans are actually getting richer at the national level. What gives? Although those of highest socioeconomic status do tend to be taller, there is still a large underclass pulling the average down in the stature charts. We still have 9 million people with no job (5.5% of the U.S. population), 42 million with no health insurance (13.4%), and 45 million living below the poverty line (14.5%). Further, as discussed in a 2013 New York Times article, our middle class - which comprises the bulk of the American population - is not immune to the risk of unemployment and depressed wages, both of which are indicators of suboptimal socioeconomic conditions that could negatively affect height growth. Komlos also surmised that the U.S. GDP per capita is high because the Americans who are employed work many more hours than their European counterparts, leading to lack of quality family time, fewer home-cooked meals, and possibly even neglected children. While these qualitative indicators of the social environment are difficult to quantify, it is certainly possible that they have a measurable impact on early growth and attained stature.
Poor diet & obesity. It’s likely no coincidence that our fast-food culture developed in the second half of the 20th century, concomitantly with the obesity epidemic and height stagnation. The problems of poor diet and our growing waistlines go hand-in-hand with social inequality: the poorest Americans tend to consume more processed foods and fast food. Kids in the U.S. consume more meals outside the home and more fast food high in fat and low in essential micronutrients than do European children. The high-fat, high-sugar Western diet is directly associated with obesity, which may lead to shorter attained height. Some pediatricians believe that obesity causes earlier onset of puberty. In young women, estrogen leads to the closure of growth plates at the ends of long bones, which are responsible for linear growth. If that occurs earlier, then one is at risk for being shorter as an adult.
Anecdotes. Other explanations I came across while researching this topic were that we may have reached our “full genetic potential for height” and that these trends are simply natural fluctuations of the leveling-off process. Others believe that the answer to the puzzle is immigration. As more Latin/Mexican Americans and Asians enter the U.S., they lower the average height. This makes sense, especially since immigrant populations tend to live in poorer socioeconomic conditions. However, this possibility has been dismissed, since at least one study included data only on native-born Americans who spoke English at home, excluding persons of Asian and Hispanic descent.
Should we be worried? A few inches difference in height is likely not a major health issue, but America’s relative shortness does suggest that something is awry with our way of life – whether it be the dual burden of unemployment in the face of excessive work hours, or our increasing BMIs in the face of poor nutrition.