Sugar, seed oils, and avoiding sickness: your health questions answered

At a recent ceremony for world leaders in Beijing, a hot mic picked up a surprising exchange between Vladimir Putin and Xi Jinping about the possibility of living to 150. Putin suggested the secret might lie in repeated organ transplants. But is this the new frontier of anti-ageing research or a fringe and unproven theory? To find out, science editor Ian Sample speaks to Russian affairs reporter Pjotr Sauer and to John S Tregoning, professor of vaccine immunology at Imperial College London and author of Live Forever: A Curious Scientist’s Guide to Wellness, Ageing and Death. Help support our independent journalism at theguardian.com/sciencepod

The fertility rate in England and Wales has fallen for the third year in a row – a trend mirrored across the world, with two-thirds of the global population now living in countries with below-replacement-level fertility. In the second episode of a two-part series, Madeleine Finlay speaks to Dean Spears, assistant professor of economics at the University of Texas at Austin, and Dr Jennifer Sciubba, chief executive of the Population Reference Bureau, to ask whether declining birth rates are really something to worry about – and how societies can adapt to a future with fewer children. Watch the new Guardian documentary Between Moon Tides. Help support our independent journalism at theguardian.com/sciencepod

The fertility rate in England and Wales has fallen for the third year in a row. It is a story that is being repeated all over the world, with two thirds of the global population now living in countries with below replacement level fertility. Low fertility rates have become a talking point on the political right, with Elon Musk claiming that population decline is an existential threat to the future of humanity. But for others, the timescales involved are too vast to start worrying about now. So how should we be thinking about population decline? In episode one of a two-part series, Madeleine Finlay speaks to Dean Spears, assistant professor of economics at the University of Texas at Austin, and to Dr Jennifer Sciubba, president and CEO of the Population Reference Bureau, to find out what has happened to global birth rates, and how governments are trying to tackle the fall. Help support our independent journalism at theguardian.com/sciencepod

Psychologists have traditionally believed we become less curious as we age, but recent research has shown that curiosity actually becomes more targeted and specific in our later years. To find out why this happens, and how maintaining broad curiosity into older age can help keep our brains young, Madeleine Finlay hears from Dr Mary Whatley, an assistant professor of psychology at Western Carolina University, and Dr Matthias Gruber, of Cardiff University’s Brain Imaging Centre. Help support our independent journalism at theguardian.com/sciencepod

It’s been a dramatic week at the US Centres for Disease Control and Prevention (CDC). In the space of seven days, the agency’s head was sacked and replaced by an interim head, four senior staff members resigned, and existing staff took to the streets to express support for their ousted leaders. To understand how everything unfolded and what it could mean for the health of Americans, science editor Ian Sample hears from health reporter Melody Schreiber and former CDC director Mandy Cohen. Help support our independent journalism at theguardian.com/sciencepod