He’s best known as a perky children’s television presenter but, at 48, Dr Xand van Tulleken is feeling his age. “My knees are creaky. I’m tired. My hangovers are worse,” he says, explaining he spent most of last night with his youngest child Daphne, not yet one, awake and screaming. We’re meeting on Zoom to discuss his new book, Make Me Well: A Quest to Understand the Confusing World of Wellness, a scrupulously researched, engaging and amusing read despite the shocking weight of the revelations. Supplements? Snake oil. Blood tests? Don’t bother. Wearable tech? You may as well consult the…