Hesperian Health Guides

Causes of Mental Slowness

comparison of head sizes that are normal and too small.
normal head size
too small head size
A child with microcephaly (small brain) is mentally slow and often also develops vision, hearing, or other physical problems. See measurements of head size.

There are many causes.

  • Often the cause is not known.
  • Some children are born with a very small brain, or the brain does not grow or work normally.
  • Sometimes there is a ‘mistake’ in the ‘chromosomes’ or the tiny chemical messages that determine what a child will be like (inheritance). This is what happens in Down syndrome.
  • Sometimes a mother did not get enough of a certain food or mineral during pregnancy. (See “Hypothyroidism”.)
  • Brain damage can happen either before, during, or after birth. In addition to being mentally slow, these children may also have cerebral palsy, blindness, deafness, or seizures. Common causes of mental slowness from brain damage are discussed in Chapter 9, and include:
    • German measles during early pregnancy
    • meningitis (brain infection) from bacteria, tuberculosis, or malaria, most often during early childhood
    • hydrocephalus, often with spina bifida
    • head injuries
    • other causes include brain tumor, poisoning from lead, pesticides, certain medicines and food, and some forms of muscular dystrophy or atrophy

In many parts of the world, the most common causes of mental slowness are brain damage and Down syndrome. But in some mountainous areas, it is very often caused by lack of iodine in food and water.

Usually there is no treatment for mental slowness. Therefore, we often do not need to know the exact cause. Instead, we need to help the child develop the best he can. However, in some cases, certain medicines, changes in diet, or prevention of further poisoning can make a big difference. If a child has any signs of hypothyroidism or seems to be gradually losing mental ability, try to get expert medical advice.

Prevention of mental slowness is discussed with its different causes. See especially cerebral palsy, Down syndrome, and hypothyroidism.

This page was updated:21 Nov 2019