<P> A study of the regions of the world known as blue zones, where people commonly live active lives past 100 years of age, speculated that longevity is related to a healthy social and family life, not smoking, eating a plant - based diet, frequent consumption of legumes and nuts, and engaging in regular physical activity . In a cohort study, the combination of a plant based diet, normal BMI, and not smoking accounted for differences up to 15 years in life expectancy . Korean court records going back to 1392 indicate that the average lifespan of eunuchs was 70.0 ± 1.76 years, which was 14.4--19.1 years longer than the lifespan of non-castrated men of similar socio - economic status . The Alameda County Study hypothesized three additional lifestyle characteristics that promote longevity: limiting alcohol consumption, sleeping 7 to 8 hours per night, and not snacking (eating between meals), although the study found the association between these characteristics and mortality is "weak at best". There are however many other possible factors potentially affecting longevity, including the impact of high peer competition, which is typically experienced in large cities . </P> <P> In preindustrial times, deaths at young and middle age were more common than they are today . This is not due to genetics, but because of environmental factors such as disease, accidents, and malnutrition, especially since the former were not generally treatable with pre-20th century medicine . Deaths from childbirth were common for women, and many children did not live past infancy . In addition, most people who did attain old age were likely to die quickly from the above - mentioned untreatable health problems . Despite this, we do find many examples of pre-20th century individuals attaining lifespans of 72 years or greater, including Benjamin Franklin, Thomas Jefferson, John Adams, Cato the Elder, Thomas Hobbes, Eric of Pomerania, Christopher Polhem, and Michelangelo . This was also true for poorer people like peasants or laborers . Genealogists will almost certainly find ancestors living to their 70s, 80s and even 90s several hundred years ago . </P> <P> For example, an 1871 census in the UK (the first of its kind, but personal data from other censuses dates back to 1841 and numerical data back to 1801) found the average male life expectancy as being 44, but if infant mortality is subtracted, males who lived to adulthood averaged 75 years . The present life expectancy in the UK is 77 years for males and 81 for females, while the United States averages 74 for males and 80 for females . </P> <P> Studies have shown that black American males have the shortest lifespans of any group of people in the US, averaging only 69 years (Asian - American females average the longest). This reflects overall poorer health and greater prevalence of heart disease, obesity, diabetes, and cancer among black American men . </P>

Which of the following has contributed to longer life spans in the united states