The validity of Blue Zones demography: a response to critiques.

Blue Zones are geographically and temporally defined areas with a history of disproportionately high concentrations of nonagenarians and centenarians. Nearly two decades ago, these zones gained international attention when the Blue Zone term was introduced in seminal articles published in Experimental Gerontology and National Geographic. Since then, numerous scientific papers have extracted valuable insights into human health from investigating the long-lived people who live there. However recently, validity of the ages of people living in the Blue Zones has been questioned. Here, we address these concerns by describing in detail the age validation process undertaken in Blue Zones and comparing it to the prevailing standards in gerontological demography. As discovered a century and a half ago, most self-reported claims of exceptional longevity are false. However, using methods developed by gerontological demographers over the past decades, the true age of people claiming exceptional longevity can be determined by cross-checking multiple independent documentary sources. This procedure minimizes, and usually eliminates, errors due to fraud, honest mistakes, poor memory, or identity switches, especially between homonymous siblings. All Blue Zones described herein have been extensively validated based on thoroughly cross-checked data from multiple independent sources plus state-of-the-art demographic methods. Consequently, age data from these Blue Zones are valid and reliable.