The persons with strong immunity fell less prone to diseases. Poor diet will result in a weakened immune system. Others factors such as stress, smoking, excess alcohol and caffeine, food additives, pesticides, pollution, lack of sleep and exercise also weakens the immune system.
Eat healthy food such as fresh fruits and vegetables, sprouted seeds, raw nuts and whole grain cereals. Stay active, do exercise daily and take proper sleep.
Squeeze half a lime in a glass of lukewarm water, add one teaspoon of honey. Take daily first thing in the morning for some months.