In the south of Japan, the little paradise of Okinawa is nicknamed “the island of centuries”. In Italy, it is Nuoro, province of Sardinia, which is famous for the longevity of its inhabitants. Along with the Greek island of Ikaria, the Nicoya Peninsula in Costa Rica, and the Loma Linda Adventist community in California, they have been described by American journalist and explorer Dan Buettner,(New window) like “blue zones”, these places on Earth where centenarians are much more numerous than on the rest of the planet.
For several years, they have been the subject of wide media coverage, like the series 100 years of plenitude: the secrets of the blue zones released on Netflix in August 2023. However, according to a study pre-published (i.e. not yet peer-reviewed) in March, carried out by researcher Saul Justin Newman, from the University of Oxford (UK -Uni), this is nonsense.
More broadly, the specialist in population aging scrutinized demographic data on centenarians in the United States, Italy, England, France and Japan. He deduced that “the data on extreme human aging is rotten the interior”due to methodological errors and problematic sources, he explained to online media The Conversation. In September, his revelations earned him an Ig Nobel Prize, a parody award awarded to serious research, but “so surprising that they make you laugh, then think”as the official website explains.
Franceinfo interviewed several demographers on the main arguments put forward by Saul Justin Newman. In most cases, they express their disagreement.
Demographers work on erroneous data: unfounded
Contacted by franceinfo, Saul Justin Newman castigated the methodology of demographers, affirming that their “validation” simply consists of “check the consistency of the documents”which leaves “undetectable errors” when these are “erroneous”. In his study, he mentions, for example, the significant absence of death certificates in the United States for people described as centenarians.
The criticism is “unfair”according to France Meslé, emeritus research director at the National Institute of Demographic Studies (INED) and member of the steering team of the international database on longevity (IDL), which counts semi-supercentenarians (105 at 109 years old), and supercentenarians (from 110 years old). She assures that researchers will “far beyond simply verifying a birth certificate” for supercentenarians. “We follow their life cycle to see if they got married at a consistent age, if they had children at a plausible age”she explains.
Michel Poulain, demographer at the Catholic University of Louvain (Belgium), cites the case of an Irish supercentenarian for whom he found around sixty coherent pieces of information. With Italian researchers, he brought out the concept of “blue zone” in a 2004 study on Sardinia. As part of his research, he only detected one error: the case of Damiana, a centenarian who was in reality 107 years old instead of the validated 110 years old. His findings on the exceptional longevity of Sardinian mountain dwellers were validated by two other demographers, the Quebecois Bertrand Desjardins of the University of Montreal and Bernard Jeune of the University of South Darnemark, in a 2006 report of which franceinfo has taken note.
French semi-supercentenarians do not have birth certificates: false
In his study, Saul Justin Newman ensures that none of the 365 French semi-supercentenarians listed by the IDL database “does not have an original birth certificate”. “This is obviously false.“, retorts François Robin-Champigneul, independent researcher. “All French centenarians listed by the IDL are validated with a birth certificate”specifies the scientist, who was one of the peers responsible for rereading an old version of Saul Justin Newman's pre-publication, where the same argument was already put forward.
“Civil status in France was established by François I in the 16th century”recalls Jean-Marie Robine, co-responsible for the IDL database and research director at the National Institute of Health and Medical Research (Inserm). Since the French Revolution, two sources have made it possible to verify the age of a centenarian: municipal registers and parish registers, recalls the demographer.
In the United States, birth certificates have caused the number of supercentenarians to fall: misleading
Analyzing data from the Gerontology Research Group (GRG), Saul Justin Newman suggests that “the introduction of birth certificates” at the beginning of the 20th century in the United States could explain a drastic drop in the number of recorded numbers of supercentenarians. “When these states move to statewide birth registration, the number of supercentenarians drops by 80% per year”he explains in his pre-publication, suspecting a problem of fraud.
The collection of data on births at the national level did not begin until 1902, recalls the American Bar Association. The current system took almost twenty years to develop, “between 1915 and 1933, when all States participated”. “If you were born in a western state, and you're 95 years old today, there's every chance you don't have a birth certificate, because it didn't exist.”summarizes Jean-Marie Robine.
However, François Robin-Champigneul believes that the rarity of supercentenarians in the United States is due to the late establishment of civil registration in 37 states, making it impossible to register supercentenarians before a certain date. For the demographer, this explains the drastic drop observed by Saul Justin Newman, once only the new system is taken into account. The problem is still relevant today, he explains: in states where birth certificates were introduced in 1915, supercentenarians will only be able to appear officially from 2025. In other words, it is more a question of a technical reason than a question of data reliability.
In Japan, there were 82% of false centenarians in 2010: false
In his pre-publication, Saul Justin Newman criticizes the reliability of Japanese population statistics: “In 2010, more than 230,000 Japanese centenarians were missing, fictitious, victims of administrative errors or dead”, indicates the researcher, estimating the proportion of “false centenarians” at 82%. That year, the country announced that 234,354 people listed as theoretically centenarians in the local civil registry could not be found. Among them, citizens who died during the Second World War or in the post-war period, and whose death had not been reported to the Japanese civil registry.
However, François Robin-Champigneul disputes the percentage put forward by Saul Justin Newman. For the French researcher, his colleague mistakenly considers the “koseki”the family register to authenticate the civil status of a person, such as a database of centenarians, when in reality, the two official sources for doing this are the national census, taking place every five years, and the resident register.
“It takes the potentially centenarian population according to the kosekiand divides it by that which has always been officially counted as centenarians [via le recensement national]”, explains the researcher. In other words, according to him, Saul Justin Newman mixes two different databases. This gives a “ratio which in no way represents a proportion of false centenarians”he judges.
For François Robin-Champigneul, the official number of centenarians in Japan taken from the national census has never been debated. According to the Japanese Ministry of Health, the country had more than 95,000 centenarians, 88% of whom were women in September 2024.
The “blue zones” are an urban legend: to be qualified
Saul Justin Newman criticizes, to franceinfo, the “promoting the Okinawan way of life for twenty years”. LAmerican journalist Dan Buettner has in fact developed and marketed the concept of “blue zones” throughout the world for two decades. (with the scientific assistance of Michel Poulain from 2005 to 2017). However, in addition to the Californian area of Loma Linda, which has never been scientifically founded, areas of youth like Okinawa and Costa Rica, once relevant, today seem to be showing their limits.
For example, a 2024 study by Michel Poulain shows that longevity in Okinawa has declined, with the prefecture falling from fourth to 26th place in 2002 in terms of life expectancy among men. “There is a split between those born before 1947 and those born after 1947”notes the Belgian demographer to franceinfo. “The Blue Zone of Okinawa is more a matter of the past than a matter of today”summarizes his colleague Jean-Marie Robine. Both call into question the westernization of the diet.
In Costa Rica, the trend is similar. The “blue zone” of Nicoya also saw its longevity drop for those born after 1930, according to a study published in 2023 by demographer Luis Rosero-Bixby, who contributed to the recognition of this “blue zone” in 2007. “Twenty years ago, there was no McDonald's or Burger King. Now, all these fast-food brands are there. Young people prefer sodas to local juices”once again illustrates Michel Poulain.
For François Robin-Champigneul, the definition of “blue zone” is a bit too vague regarding the degree of concentration of centenarians retained. “Are we talking about one and a half times more, two and a half times more people in a cohort [population étudiée] having reached the age of 100 within a given area, compared to the rest of the territory ? This deserves to be clarified.”he believes.
“I’m sure there are areas where people live longer.”however, assures the researcher. The demographers interviewed by franceinfo are now turning to the Antilles. Michel Poulain has thus identified Martinique as a new “blue zone” on his site. There are twice as many centenarians there as elsewhere in France, he writes.
