Supplements. Note the name. They're not handy replacements for a healthy diet and lifestyle; they're a nice top-up of the nutrients you need to keep skin, hair and nails in good nick – usual suspects such as vitamins A, C and E plus minerals such as zinc, iron and silica.
Possibly just as important is the psychological support: popping a few pills at breakfast time – especially ones expressly linked to your vanity that you've forked out a good few quid for – provides a convincing nudge towards wiser choices.
In the same way that personal training is often just an expensive way of keeping your appointment with a kettlebell, taking morning supplements helps move your brain into that zone where porridge seems a better breakfast than cold pizza.
The strong and sensible don't need this kind of thing, but weak-minded folk like me do, and if – one way or another – it makes my skin and hair nicer, that's just fine by me.