The 2024 World Population Prospects reports that the number of centenarians has roughly doubled every decade since 1950 and is expected to quintuple by 2050. Lifespan is shaped by genetics, lifestyle, environment, and social factors, but the exact reasons some reach 100 remain largely unknown.

A groundbreaking Swedish study tracked 44,637 people for up to 35 years, following routine blood tests taken in midlife. Of these, 1,224 reached 100, most of them women. The study found that moderate, stable levels of glucose, cholesterol, iron, kidney and liver function, and low inflammation were linked to greater odds of longevity. Extremes in any of these markers reduced chances.

Genetics also play a role, with genes like FOXO3A, APOE, PON1, TP53, and P21 affecting stress resistance, cardiovascular health, and cell repair. Blood type may have minor influence, but lifestyle and habits over decades remain crucial.

The takeaway: longevity isn’t about perfection but steady, balanced habits—healthy meals, sleep, movement, stress management, and avoiding extremes. Small, consistent choices over a lifetime quietly compound to increase your odds of living longer and healthier.