It’s my goal to live to 100 – and it’s not just diet and exercise that will help me achieve it | Devi Sridhar

Every time my mind goes down the optimisation' route, I'm reminded of my job as a public health scientist, looking into the factors that affect how long we will live

• Prof Devi Sridhar is chair of global public health at the University of Edinburgh, and the author of How Not to Die (Too Soon)

For much of the past century, life expectancy continually increased. In most countries in the world, children could hope to live, on average, longer, healthier lives than their parents. This expectation is still true of the mega-wealthy. In fact, tech billionaires and multimillionaires have recently been fixated on finding the secret to longer life, convinced that with enough money, technology and cutting-edge science, they can stave off the inevitable for a few more decades to reach 120 or even 150 years old.

But their efforts aren't trickling down to the rest of us. The world's health crises are getting worse, with life expectancy going backwards in several high-income countries, such as the UK and US. In Britain, stagnation started before the Covid pandemic and has decreased by six months, and in the US by 2.33 years. Obesity rates are rising - not just in wealthy countries, but also in places like Ghana, which has experienced a 650% increase in obesity since 1980. Not 65%; 650%. Clean air is a rarity in most places in the world. Mental health conditions like depression are on the rise, worsened by financial precarity and stress.