I am training to walk a marathon i am up to 14 miles. my feet are swollen, first time this has happened.should i be worried?

Get examined: The bigger question is wheter or not you are retaining fluids or have a circulatory issue: please get a medical exam and clearance before the marathon.

If painful: If you have swelling and pain, it might be looked at to rule out a possible stress fracture. There are medical reasons for swelling, especially if the ankles and legs are affected as well, and seeking care can rule these issues out.

Painless swelling..: Walking 14 miles is liable to make a lot of peoples feet swell, just saying. More information is need as to the extent of training you have been doing and the nature of the swelling in severity and duration. See if walking a few days at less distance gives the same results. You might have to consult with a sports specialist at Healthtap to ease your concerns.

I am not sure: of your age, I would ask is there any chance you are pregnant? if not, I Would ask if you are in any pain (in the feet), make sure your sneakers are correct size. Have you been running more than usual in order to increase your mileage? Are you careful with your salt intake? do you take any medications?