Reasons Younger Children Outgrow Older Siblings

It is interesting to observe the growth patterns of siblings who are spaced a few years apart. During one stage, the height and weight of the younger sibling may catch up with and surpass that of the older sibling. Later, the older sibling may have a sudden growth spurt and become the taller of the two. Many parents question the cause for their younger child's outgrowth of the older child. It turns out that various factors account for a younger child outgrowing his sibling including DNA, hormones, diet, illnesses/medications, and psychosocial environment.

DNA

As explored in Biology class, one's genetic makeup is transmitted to him at conception through DNA (deoxyribonucleic acid). An individual's DNA is responsible for all of his traits including height and weight; so regardless of age, a child's growth depends on the distinct genes inherited from both parents.

Diet

Diet plays a huge role on child growth. In particular, meat and milk contain nutrients that are vital to a child's development. According to a study among Kenyan children, conducted by Lindsay Allen of the University of California, children who consumed an additional 60 grams of meat over a two-year period became 400 grams heavier and 80% stronger on average than their counterparts who did not consume these meat supplements. In addition, children who were given a cup more milk were 40% stronger than those who did not receive these milk supplements. It is important to note that when eating habits differ among siblings, it is often due to personal preferences rather than availability of nutrient-dense foods. So a younger child who loves to eat meat has the potential to outgrow his slightly older sibling who cares less for meat.

Illnesses/Medications

Differences in the quality of health among siblings largely impact their rates of growth. Illnesses that interfere with child growth include heart and lung, kidney, blood deficiency (anemia), and digestive tract diseases. Specifically, digestive tract diseases result in the inability to absorb nutrients from foods as characterized by the symptoms of vomiting, diarrhea, or constipation. In connection to illnesses, medications that are consumed in large doses or for prolonged periods often hinder a child's growth.

Hormones

Three hormones contribute to a child's growth and development: 1) Thyroxin: formed in the thyroid gland in the neck to control growth and metabolism; 2) Cortisol: formed in the adrenal glands above the kidney to control glucose levels, fat accumulation, and bone strength; and 3) Growth Hormone: formed by the pituitary gland at the base of the brain to control protein creation, fat and glucose metabolism, and bone growth. While an excess of Cortisol stunts growth, a lack of Growth Hormone inhibits growth and results in a child becoming overweight for his height and appearing younger than his age.

Psychosocial Environment

A child's psychosocial environment affects growth in instances where an older sibling feels neglected or overstressed while the younger sibling has more emotional support from parents. According to the Magic Foundation, the older child's growth becomes delayed until his emotional needs are met.

Taking into account all of these factors that affect a child's growth and development, parents should not be alarmed when their younger child outgrows his older sibling. Each child's rate of growth differs due to heredity, nutrition, health, hormones, and environment. Further, while a younger child may grow more rapidly due to early puberty, the older sibling has the potential of surpassing the younger sibling in height at a later stage.