1. No Breakfast – People who don’t eat breakfast have lower blood sugar levels. This can lead to an insufficient supply of nutrients to the brain (and to underperformance in terms of thinking, processing , retrieval and memory skills).
2. Overreacting – This can flood the brain with chemical which interferes with clear thinking, logical analysis and memory.
3. Smoking – This can cause a shrinkage in the brain, and possibly lead to Alzheimer’s disease.
4. High Sugar Consumption – Consuming too much sugar interferes with the absorption of proteins and nutrients. These are essential for healthy brain development.
5. Air Pollution – The brain is the largest oxygen consumer in our body. Inhaling polluted air decreases the supply of oxygen to the brain. Again, this can reduce and interfere with the brain’s healthy functioning.
6. Sleep Deprivation – Sleep allows our brain to rest and rejuvenate itself. Long term sleep deprivation accelerates the death of brain cells. It interferes with putting down new memory traces, effective problem solving and memory retention.
7. Exercising your Brain in Times of Illness – Working or studying during times of sickness can lead to a ineffective thinking, poor processing, and to poor memory and retention.
8. Lack of Stimulation – Thinking is the best way to train our brain. Lack of stimulation can prevent new neural pathways from forming. It can also prevent us from reaching our potential in terms of creative thinking and analytical thinking.

Source: The World Health Organisation