From fountain-searching Ponce de Leon to pill-popping Silicon Valley techies humanity has been trying to pinpoint the answer for centuries, often fixating on all the wrong things: miracle diets, miracle foods, miracle supplements.

We skip gluten and invest in exercise gadgets.

We swallow vitamins. We obsess about BMI. While healthy nutrition and physical activity are indeed important for health, there are things we all too often sacrifice in favour of fad diets that have an outsize impact on our centenarian potential.

Friendships. Purpose in life. Empathy.

Kindness. Science shows that these 'soft' health drivers are often more powerful than diet and exercise. Consider the numbers: studies show that building a strong support network of family and friends lowers mortality risk by about 45 per cent.

Exercise, on the other hand, can lower that risk by 23 to 33 per cent. Eating six servings of fruit and veg per day can cut the danger of dying early by 26 per cent, while following the Mediterranean diet by 21 per cent. For volunteering, it's 22 to 44 per cent.

Many more examples like this led Marta Zaraska to her ultimate conclusion: you should be contemplating your purpose in life, not the best fitness tracker to buy. Humans are social animals. Over the course of our evolution we've developed intertwined systems that regulate our social lives on one hand and our physiology on the other, contributing to our centenarian potential.

The amygdala and the insula in the brain, the social hormones oxytocin and serotonin, the vagus nerve, the HPA stress axis - these all link our bodies and our minds, contributing to our centenarian potential. We feel safe when we are surrounded by friendly others. The nervous system, the gastrointestinal system, the immune system all function properly when the tribe is there for us and when we are there for the tribe.

We flourish as part of a group. Marta Zaraska based Growing Young on hundreds of research papers and on interviews with dozens of leading scientists from fields as diverse as molecular biochemistry, cyber psychology, marketing and zoology. The book's research took her to rather unexpected places, too: catching wild mice in the woods of England, sipping super-smoothies at a longevity bootcamp in Portugal and arranging flowers with octogenarians in Japan.