As colds, coughs and the dreaded flu swamp Britain, Sian Williams and Dr Ranj focus this week on helping to tackle winter maladies without spending a fortune. With the money spent on vitamins similarly spiking at this time of year, Sian Williams teams up with her more sceptical dad to test the biggest selling supplements to see what is worth it and what is not - for vitamin fan Sian, is her costly daily dose doing her any good?