Final answer:
Both social isolation and cigarette smoking have been proven to increase mortality rates, with smoking being the leading cause of preventable death in the U.S., and social isolation significantly increasing the likelihood of death even when controlling for other factors.
Step-by-step explanation:
Research indicates that both social isolation and cigarette smoking are significant health risks that increase mortality. Social isolation can have serious effects on one's health; as evidence shows, men and women with the least amount of social contacts are respectively 2.3 and 2.8 times more likely to die than those with stronger social networks. This remains true even when accounting for other health factors like smoking and alcohol consumption.
However, smoking presents its own grave risk, being the leading cause of preventable death in the United States, with regular smokers suffering a significantly shortened lifespan, dying about 10 years earlier than non-smokers. Smoking has been linked to a range of serious health issues, including numerous cancers, cardiovascular diseases, respiratory diseases, and complications with infections and chronic kidney disease, all contributing to its high fatality rate.
While bone marrow transplants do carry risks, they are a treatment procedure rather than a lifestyle choice or condition, and thus not directly comparable to risk factors like smoking or social isolation in terms of broad risk of death.