Overview: You can't feel it or see it. You can't take its pulse or its temperature. But out of sight and out of mind, your immune system is working to protect you from infectious bacteria, viruses, injuries and a host of other nasties. Due to the coronavirus, the health market has exploded with products promising to boost, support or supercharge our flagging natural defences. But which of these so-called miracle products, superfoods and supplements should we be spending our cash on, and which really have the science to back up their claims? Now, as Dr Ronx Ikharia finds out, new science is revealing that the human body’s most extraordinary structure – a complex fighting system powered by five litres of blood and lymph – has the capacity to be supercharged and improved if we have the science know-how to do it. This is the definitive guide, not only to defending yourself against Covid-19, but also boosting your strength for when the cold and flu season is upon us.