Any kind of ailment or infection can or does enter the body, when there is a lack of check (either physical or automated, by the system), this state is normally there when the focus of the person and hence the energy usage has been changed from existential to counter a situation. If the body can be relaxed during the demanding times, then the possibility of any kind of infection is very trivial.
Metabolism, is one of the most important processes of the body, whose clinical parameters are direct indications of what is the stress levels which the body is going through, these stress levels apart from retarding/hyper the metabolism rate of the body also affects the release of the lymphocytes. These relevance of the lymphocytes, can be understood better as they being “watchman” of the brain within the body, these lymphocytes communicate with the brain and the central nervous system whenever they notice any kind of infection in the system, thus making the brain release T cells who then act upon the infection.
If there is stress on the body, may it be emotional, physical or psychological the body changes its behaviour as then the sympathetic nervous system and automatic nervous system takes over the control, and the entire energy (glucose) of the blood, muscles is used to cope up with that stress, which means that metabolism, immunity is directly effected.
By doing yoga exercises, either breath based or concentration centric, the manicure chakra (solar plexus), anahata chakra ( heart chakra), vishudhi chakra (throat chakra) are energised, hence cleansing the conduits which carry the energy and chemicals to and fro from these chakras, and hence the body retains its optimum levels. These exercises lead the brain, central nervous system and the associated parts, like amydala, frontal hippocampus to release right quantity of serotonin and neoprene hormones which make the body ease, thus metabolism and lymphocytes ( one of the most crucial factors for health) remain in healthy density.