By Zahna Eklund Making one change to the way you shower this winter could help you fight off illnesses this winter, according to TV doctor and health guru Michael Mosley. Doctor Mosley is known for popularising the 5:2 diet and creating the Fast 800 diet, but he’s now shared his wisdom on another area of our health – our immune system. According to the health expert, making one simple swap could improve our well-being, although it might not sound too appealing, as you’ll need to take a cold shower. Amid all the wet and cold weather we’ve been having, there’s nothing better than coming home and…