A recent study by John Cacioppo from Chicago University illustrates that loneliness can increase "the blood pressure of those nearing retirement age to the same degree as smoking or a sedentary lifestyle".
The study explained on the New Scientist web site (and nowhere to be found on the Journal of Psychology and Aging web site at this moment!) expands on a previous study and collected data. It indicates that social connections are an important element of the lonely factor and perceived and real social connections are sometimes misleading as are people perceived as outgoing and how isolated they sometimes feel...