Pathogenic agents such as cigarettes and excess alcohol naturally damage and lower the defences of the immune system. Immune cells are produced in the bone marrow. Their number decreases in time not only because of external pathogenic factors but also due to the weakening of the bone structure, operations, diseases...
To boost your immune system it is recommended to eat more colourful vegetables. Think about taking vitamin C as well.
Considered as a powerful antioxidant, vitamin C is actively involved in protecting the cardiovascular system. It effectively fights against inflammatory and infectious disorders by increasing the mobility of white blood cells and by stimulating the immune system.
Vitamin D stimulates the immune system by creating the favourable conditions to the secretion of antimicrobial peptides and by reducing the development of autoimmune diseases.