What are the Blue Zones, and what is actually true about them?

Blue Zones are geographically defined areas where, historically, more people in their nineties and hundreds live than elsewhere. The best known are Ogliastra (Sardinia), Okinawa (Japan), the Nicoya Peninsula (Costa Rica) and Ikaria (Greece). The first three are the best documented; for several other regions that are sometimes presented as Blue Zones, the evidence is insufficient or contradictory.

There is a serious debate about the reliability of the age data. Critics argue that the high numbers of centenarians are partly explained by administrative errors or fraudulent registration, especially in areas where civil records were historically unreliable. Researchers who defend the Blue Zones say the ages have been verified through multiple independent sources. That debate has not been settled, and it undermines confidence in the 'true' longevity figures for these regions.

The lifestyle picture in Blue Zones is more consistent. Residents exercise regularly, have strong social networks and a positive outlook on life. In Ikaria and Sardinia, older residents more often reported good health, more often lived with a partner and had strokes less frequently. Whether that lifestyle is the cause of long life, or the other way around, cannot be established with certainty.

The Blue Zone diet, which is high in fibre, polyphenols and unsaturated fats and low in red meat, is regularly put forward as an explanation. In Ikaria, coffee, tea, fruit and olive oil were inversely associated with cardiovascular disease in older adults. The biological mechanism is plausible: these nutrients inhibit inflammatory processes that play a role in ageing. But the eating patterns in these regions are less uniform and timeless than they are often presented, and they change over the years. Simple 'copy the Blue Zone diet' advice is therefore less solid than it appears.

Genetics also plays a role, but does not appear to be decisive. In Ikaria and Sardinia, certain risk variants of genes that influence Alzheimer's disease and ageing occurred less frequently than in other populations. Yet the available research points to lifestyle and environment as the primary factors. Large-scale comparative studies are lacking, and poverty, isolation and possible under-reporting of deaths have never been properly ruled out as alternative explanations. The Blue Zone concept offers interesting clues about life and health at an advanced age, but it is not a scientifically proven blueprint.