Identifying and Confirming Blue Zones

National Geographic’s groundbreaking cover story on the blue zones was the first mainstream media piece that identified geographically defined and demographically confirmed areas where people live statistically longest. The story became one of the magazine’s most popular stories, in part, because of the rigor with which the researchers verified ages.

The process involved looking through worldwide census data for areas of high concentrations of people surviving over age 90.

1. In suspected blue zones, researchers go into the town hall to examine birth records dating back 120 years. For every person surviving past 90, we cross-reference their birth record to the birth certificate and then, often, the baptismal records. So, we’re sure when they were born.
2. Then we look at the death records of people who survived over age 90 to ensure their death is recorded accurately. Again, we cross-reference the death record with the death certificate and often visit the grave. So, we’re sure when people died.
3. If the person age 90 is still alive, we go visit them. In some cases, they emigrate, in which case we find family members to confirm they’re still alive.
4. After age verification, we can tabulate the total number of people who have survived over 90 and divide it by the total number of births in that period. That gives us a percentage we can compare internationally. We don’t just count the number of 90+ people living today because that would allow for selection bias (e.g., Naples, Florida, where an influx of rich retirees would skew the numbers).

This is a long, tedious process that took us years, for which our team received two National Geographic Explorer grants. But it absolves us from criticisms of age exaggeration or other types of fraud.

Here are eight peer-reviewed articles in respected academic journals which underpin our blue zones. They describe or attest to our age validation process.

1. Poulain M, Pes GM, Grasland C et al. Identification of a geographic area characterized by extreme longevity in the Sardinia island: the AKEA study. Exp Gerontol. 2004;39:1423-9. LINK
2. Poulain M, Herm A, Errigo A et al. Specific features of the oldest old from the Longevity Blue Zones in Ikaria and Sardinia. Mech Ageing Dev. 2021;198:111543. LINK
3. Rosero-Bixby L, Dow WH, Rehkopf DH. The Nicoya region of Costa Rica: a high longevity island for elderly males. Vienna Yearb Popul Res. 2013;11:109-136. LINK
4. Rehkopf DH, Dow WH, Rosero-Bixby L, Lin J, Epel ES, Blackburn EH. Longer leukocyte telomere length in Costa Rica’s Nicoya Peninsula: a population-based study. Exp Gerontol. 2013;48:1266-73. LINK
5. Poulain M, Pes GM, Carru C et al. The Validation of Exceptional Male Longevity in Sardinia. In: Robine, JM., Crimmins, E.M., Horiuchi, S., Yi, Z. (eds) Human Longevity, Individual Life Duration, and the Growth of the Oldest-Old Population. International S LINK
6. Cockerham WC, Hattori H, Yamori Y. The social gradient in life expectancy: the contrary case of Okinawa in Japan. Soc Sci Med. 2000;51:115-22. LINK
7. Willcox BJ, Willcox DC, Todoriki H, et al. Caloric restriction, the traditional Okinawan diet, and healthy aging: the diet of the world’s longest-lived people and its potential impact on morbidity and life span. Ann N Y Acad Sci. 2007 Oct;1114:434-55. LINK

For more information, see: The Science Behind Blue Zones: Demographers Debunk Critics