Children who are short for their age may perform more poorly on tests of intelligence than their taller peers, a new study suggests. The findings, say researchers, imply that some environmental factors may negatively affect both early childhood height and mental development.

What those factors are is uncertain, but a stressful home life is one possibility, according to Dr. Scott Montgomery of the Karolinska Institute in Stockholm, Sweden, the study’s lead author.

“Childhood stress can slow growth significantly,” he told Reuters Health, pointing to evidence that children’s growth can be impaired when parents divorce or frequently argue. Research suggests that long-term stress can affect the body’s production of growth hormone - and, therefore, a child’s height.

Similarly, Montgomery explained, stress can influence the development of brain regions involved in memory and learning.

Of course, short stature need not signal any underlying problem. Some children are simply shorter than average, particularly if their parents are not tall. “Some children are shorter for genetic reasons,” Montgomery said, “and this will not influence their intelligence.”

His team’s study, published in the Archives of Disease in Childhood, included more than 1,400 British children born in 1970. Each child’s height was recorded at the ages of 22 months and 5 years, and all completed a standard test of mental acuity at the age of 10.

The researchers found that shorter height at age 5 was associated with poorer test performance at age 10 - regardless of factors such as birth weight and family income.

The implication, according to Montgomery, is that slower childhood growth is somehow associated with “lower intelligence.” Poor nutrition is a potential reason, he noted, but among healthy children in a developed country like the UK, stress may be a more important factor.

“A happy childhood is likely to enhance both physical growth and intellectual growth,” Montgomery said.

SOURCE: Archives of Disease in Childhood, January 2006.