Thermal underwear should be at the top of the list here. Although thermals provide some insulation, their main job is to fight evaporative cooling by removing the sweat away from the skin. Now that we have the briefs out of the way, we'd also need to wear a t-shirt, wind pants, a lightweight running jacket, tight fitting beanie and scarf, running tights, two pairs of socks (This is fairly important during winter to ensure decent blood flow) and then of course your favourite pair of running shoes. Keep in mind that road surfaces tend to slicken up during winter and the possibility of slipping on the tarmac or side walk increases dramatically.
As always, getting the muscles ready for some action is very important. The importance thereof should be amplified when nipping out for a quick jog at 3°C.
How Cold is too Cold
Don't try and be a hero by bursting through the gate into -30°C weather. There are always alternatives to this. And if you feel the need to go for a jog then keep the route close to home in case of an emergency.
A to Zinc the Old Fashioned Way
Preventive measures are definitely far better than the solutions, and that goes for falling ill during jogs in the cold. Multi-Vitamins have been proven to be a big waste of money as your body simply disposes of all supplements without absorbing any of it. Instead, take in these necessary nutrients by eating correctly. After all, food is the fuel our bodies run on and if you fill up with bad stuff you're going to have maintenance problems in the long run.