This is actually a pretty common occurrence and there are a few things that could be causing it:
- The fit of your shoes
It is most likely that your shoes are to blame. It could be that they aren't the right fit, or that they are laced up too tightly. Try changing the lacing and if that doesn't work get fitted for trainers at a specialised running shop. Make sure the shoes are a suitable width and there's a bit of wiggle room!
- Your clothing
Tight leggings or shorts can hinder circulation in the legs and may result in coldness in the extremities. In this instance, try wearing leggings specifically tailored for runners and try compression socks to help improve circulation.
- The material of your shoes
If the material of your trainers is particularly thin (perhaps you are wearing the same shoes all year round, for example, rather than having a winter/summer pair) it may mean you feel the cold more in your toes. Thin material is also much more likely to let in water. I suggest trying out a Gore-Tex shoe for winter running as this prevents any water from seeping into the shoe and actually helps to keep the feet warm as well.
- You aren't warming up properly
Ease into your run and get the blood circulating by doing a warm-up before heading out for a run. Failing to do this could be a contributing factor in your issue with numb toes! Try some stretches and then get the heart rate up with the lines of high skips, star jumps and jogging.
- The way you run
Running so that the toes hit the ground, rather than the ball of the foot, is another possible reason for numb toes developing during a run. This isn't easy to fix but joining a club or speaking to an experienced runner may help you make some corrections.