How to preserve normal I.Q.!

Always I have a tendency to be clever, though I am not at all. From my childhood, I was always poor in I.Q. (Intelligence quotient); however, nowadays I try to elucidate to retain it in natural phenomenon. Our brain has complex network of neurons (brain cell) those are responsible for keeping a smart I.Q. Usually normal I.Q. should be 100 for a human. However, mentally retarded people (congenital neurodegeneration) have sometime less than 25 of I.Q., those who need full time care by family and/or by nursing home. For a normal human, after the middle age (after 40 y.o.), some natural degeneration of neurons are commenced that initiating some aberrant neuronal networking in the brain refer to decrease in I.Q. Now, it is to evaluate to retain the I.Q. after the middle age – the physical exercise, cognitive training, balanced nutrition etc. are useful natural approaches.