The main cause is what we call unrequited stress -- they don't have enough friends to mitigate the stress
Roizen, who also co-authored "You: The Owner's Manual" with Dr. Mehmet Oz, said Wednesday. "The major way most of us handle stress is through a number of techniques, but the most prominent way is to discuss it with friends." "Dr. Michael Roizen holds on to what he's said for a while: That presidents effectively age twice as fast while in office." "Both aging and stress produce similar stages in inflammation, the biological pathway that contributes to age-related diseases such as cardiovascular disease, dementia and some cancers, he said. "A person under significant stress is essentially accelerating the aging process at a biological level, and also at a genetic level," Irwin said. "It's activating the genes that drive inflammation." Research by molecular biologist Elizabeth Blackburn also has shown that as people age, telomeres -- areas at the end of chromosomes -- shorten, and that this shortening along with inflammation is "highly predictive of death," Irwin said. "Stress also produces accelerated shortening of telomeres," Irwin said." http://www.cnn.com/2011/POLITICS/08/04/presidents.aging/index.html