British researchers have found evidence that male babies who grow slowly in their first year of life have lower incomes in later life. The results hold true regardless of the socioeconomic status of the child's family, suggesting that slow infant growth may be accompanied by hampered brain development. Biological processes linked to poor growth in infancy lead to lifelong impairment of cognitive function with consequent lower occupational status and income.
Researcers at the National Public Health Institute in Helsinki, Finland studied 4,630 men born in Helsinki between 1934 and 1944. The height of each man had been measured an average of 18 times between birth and age 12, measurements that the researchers linked to records of their level of education, information about income and occupation taken from the 1990 census.
The researchers divided the men into six groups according to their length at age one. Men in the lowest group -- under 72 centimetres, or 28 inches, at one year earned an average annual salary equivalent to only about 75% of what men in the highest group, longer than 80 centimetres or 31 inches at age one, earned.
Weight at one year in boys predicts their cognitive function. Boys who grow better between birth and one have better educational achievements and they make more money when they're fifty. Since, in a democratic society, income is a test of cognitive function among other things, this is rather a striking demonstration of the critical period of growth between birth and one year.