From these calculations, we realize the environment (mainly nutrients) can only change about 2 centimeters for a given offspring's height in this Chinese population. Does that mean that no matter what happens in the child's environment, the height can never change more than this? Can special treatment and nutrient supplements increase the height further? The answer is yes. The most important nutrient for final height is protein in childhood. Minerals, in particular calcium, and vitamins A and D also influence height. Because of this, malnutrition in childhood is detrimental to height. In general, boys will reach maximum height in their late teens, whereas girls reach their maximum heights around their mid-teens. Thus, adequate nutrition before puberty is crucial for height.
In addition, although diseases of childhood can inhibit ultimate stature, human growth hormone treatments can remedy such growth defects. Height accelerated by such treatment or special supplements, however, cannot be predicted based on heritability. There are two reasons: first, heritability has not been estimated in a growth hormone-treated population. Second, genes and growth hormones can interact synergistically to affect height, i.e., their effects may not be simply adding to each other but could be multiplying the ultimate effect.
The question remains, however, why different populations of a similar genetic background might have a differing heritability. The answer is, of course, environmental effects. When a given environment maximizes the genetic potential of a population for a given trait, this population tends to have a higher heritability for that trait, and vice versa. In developed countries, nutrition for childhood development is strong, which maximizes the genetic potential for height assuming no selection or new mutations. Thus, the overall heritability estimates tend to be higher, i.e., 80 percent. In contrast, in developing countries, nutrition deficits lead to a lower heritability. The fact that the mean height of the U.S. population has almost plateaued in the past decade suggests that the nutrient environment has almost maximized the genetic potential of height, at least in this country. Improved nutrition elsewhere may have similar benefits in terms of stature.
Dr. Chao-Qiang Lai has written this article in his personal capacity and the views expressed do not necessarily represent the views of the U.S. Department of Agriculture, Agricultural Research Service.