Our genes actually wire us to need company. A recent study in UCLA revealed that loneliness desensitizes the glucocorticoid receptors, cutting off the immune control and anti-inflammatory effects of cortisol, a stress-related hormone that also helps regulate the conversion of carbohydrates to energy. This probably one reason why feeling lonely leads to higher probability can lead a series of health problems such as viral infections (see this Scientific American article).
Its all in the mind. Our thoughts and feelings does influence how our body respond.
On the other hand, studies from the Massachusetts General Hospital, Boston, US, show that meditation actually increases the thickness of the cortex in areas involved in attention and sensory processing, such as the prefrontal cortex and the right anterior insula (See this New Scientist article).