It is thought that size in humans relates to life expectancy via aspects of metabolism such as growth hormone - less growth hormone means a smaller size but longer life in mammal species. Ames dwarf mice are an example of this taken to an extreme through genetic engineering, lacking growth hormone but living more than 60% longer than their peers.

From an evolutionary perspective, an abundance of food and good health in early life or gestation is thought to trigger a more aggressive front-loading of growth and fertility - which comes at the cost of faster decline once an individual is beyond their reproductive lifespan:

Sardinians have been studied extensively looking for clue to long lifespan. In the current study researchers analyzed the role of a person's height in their eventual lifespan. The researchers analyzed the height of men when they entered the military at age 20 between the years of 1866 and 1915. A total of 685 subjects were analysed. These heights were then related to the persons eventual age at death. It was found that shorter people (shorter than 161.1 cm) lived significantly longer on average than taller people (taller 161.1cm). Furthermore at age 70, taller people lived on average 2 years less than shorter people. At age 70 each quarter inch of height reduced lifespan by one year.

The authors write: In conclusion, shorter people and taller people exhibit differences in longevity. Although a tall body generally reflects abundant nutrition and good living conditions during the growth period, this height has negative ramifications as well. Biological mechanisms indicate that a larger body places greater stress on cells, tissues, and organs, which can reduce longevity.

Link: http://extremelongevity.net/2012/09/26/shorter-people-live-longer/

Source:
http://www.longevitymeme.org/newsletter/latest_rss_feed.cfm