Information taken from: http://en.wikipedia.org/wiki/Vilcabamba,_Ecuador
Vilcabamba is a village in the southern region of Ecuador, in the Loja province, about 45 km (28 mi) from the city of Loja. The etymology of the “Vilcabamba” apparently derives from the Quichua “huilco pamba.” Huilco denotes the sacred trees, Anadenanthera colubrina, that inhabit the region and pamba is a word meaning “valley.” The area has been referred to as the “Playground of the Inca” which refers to its historic use as a retreat for Incan royalty. The valley is overlooked by a mountain called Mandango, the Sleeping Inca, whose presence is said to protect the area from earthquakes and other natural disasters.
Vilcabamba is located in a historical and scenic valley, it is a common destination for tourists, in part because it is widely believed that its inhabitants grow to a very old age. Locals assert that it is not uncommon to see a person reach 100 years of age and it is claimed that many have gotten to 120, even up to 135, which would make it an area with the oldest inhabitants in the world. It is often called the Valley of Longevity.
The reasons for this claimed longevity are not very clear. French studies have shown that the diet and lifestyle of the inhabitants may be a factor. Dr. Richard Laurence Millington Synge, a Nobel Chemistry Prize winner and the man who discovered amino acids, claims that there are remarkable medicinal qualities to be found in the plant-life in certain places near the Equator …. with the valley of Vilcabamba being one of these areas. Due to scientific chemical assay techniques, analysis has now shown that the fruit, roots and herbs of this particular Equatorial sub-area offer some of the strongest anti-oxidant protection in the world. In 1973, Dr. Alexander Leaf of Harvard Medical School introduced these remarkable people to the world for the first time in his cover story for National Geographic Magazine. 
In 1981, the Ecuadorian government hired medical journalist Dr. Morton Walker to study these people in depth. In his book, “The Secret to a Youthful Long Life”, Dr. Walker reported that his research showed the mineral rich water that the Vilcabambans drank was key to their long lives and health. Laboratory analysis of the Vilcabamba water determined that the unique balance of enriched colloidal minerals in the local drinking water was ideal for promoting optimum human health. 
Medical researchers have confirmed that the retinas of 100 year-old residents are often comparable with those of 45 year-old city-dwellers. Others suggest that the climate in the region, which is reasonably steady without much variation, or the mineral content of its drinking water is particularly healthful and explains the advanced age of its inhabitants.