The ONLY cause of concern here. is your teacher dying rapidly of acute ignorance.
Neurons dont die from reading nor other physiological activity. (nor any other cell of the brain, such as glia or oligodendrocytes etc)
The calculus of the number of cells in the brain, is also wrong, because it varies with age, and also, with cranial capacity.
Reading, if anything, will enforce our understanding of abstract or objective images, and will make our brain pathways more able to learn, (the synapses or junctions between the used neurons will enforce learning)....and easier to understand mire quickly the concepts in the paragraph we focus our attention on....
Normmally, about 300,000 neurons die per year in the healthy human being, with no effect in intelligence nor capabilities for learning....
It would be interesting to ask you teacher where he or she read such nonsense,,,,,
Your teacher will be a long living human being according with his/her theory, because sincerely, if your teacher really is meaning what you are asking....he or she will have a lenghty and long life, because of.....not reading.,....Honest