Numbness in the feet and toes when cycling can be caused by a number of things.
The most common are.
Fit of your shoe
Feet are not adequately supported
Weather and Wind chill
Which shoe is for you?
It is important before you buy a pair of cycling shoes that you are aware of what size and shape feet you have, every shoe is different in the same way that every bicycle is different so the idea is to match your foot to the appropriate shoe, for example If we measure your left and right foot we may find that your left is a 45E and your right is a 44.5E, in this case we will need to go for the bigger size to give you room in the shoe for your feet to expand ( The general mass of your foot can expand a huge amount once your feet receive adequate blood flow from an increased heart rate ) Certain Brands of shoe suit different width feet, for example Specialized/Sidi generally have a narrower fit and will better fit people within the C-D range. Shimano/Northwave/Lake tend to suit a slightly wider foot and normally range between a D-E, it is important that you try shoes thoroughly as there are big differences in the fit between different models.
Supporting your feet
Cyclists need support for there feet for several reasons, supporting the arch increases the power transfer to the pedal and also spreads the load of your foot over the whole insole rather than only supporting your forefoot and heel like a conventional insole. A top sports footbed such as the eSoles eFit model on the right has interchangeable arches to customise to almost any foot type, they also have interchangeable metatarsal pads which are a great feature for increasing blood flow to the toes and reducing the chance of getting numb feet.
Weather and wind chill
Cold weather during winter can cause numbness in feet and also the hands. Make sure you have a good pair of overshoes (booties) to help keep you warm, Most overshoes will have a thin thermal layer underneath and a wind-stopper fabric overtop.
Certain pedal/shoe combinations can be uncomfortable an the ball of the foot. Cleat positioning is very important not only for power transfer but also for cycling comfort and enjoyment. If you are getting numbness or soreness around the ball of your foot try moving your cleat back on the shoe by a couple of millimetres, you will be surprised what a difference this can make by taking the pressure of the ball ever so slightly.