Alongside my morning yoghurt and cereal, I’m taking an increasing number of supplements. The long brown ones contain lion’s mane, a mushroom supposedly good for anxiety. The tiny round one is vitamin D – in cloudy London I feel eternally deficient without this. The chewy one? A multivitamin. The powder is creatine, which my friend swears by for keeping brain fog at bay. Then there’s collagen, best known as a protein vital to youthful-looking skin, because, well, we all live in…