Everyone has health, good or bad. Giving your character health concerns will make them more real to the reader. Unless your character is a whining hypochondriac, just mentioning their overall health now and then is sufficient. The trick is not to overdo it. You only need to mention it now and then through out the work. A sentence or two here and there is sufficient. All you have to do is indicate your character’s health in some way. It can be in a description or action. A bedridden character shown in bed is enough to show the character’s health. A character can be shown exercising or taking medication in description or action. That will bring the character to life for your reader.
If your character is in good health, you can show that too. It will be in the character’s routine. Have your character own exercise equipment or show them going to the gym. Have them talk about their workout with other characters. Show them going for walks or runs. Have them use a bicycle to get around. Be careful not to overdo it. Your character’s exercise habits doesn’t need to be on every page. Your readers will remember the characters’ workout choices. You don’t even have to be detailed. Having the characters’ talk in a gym will make the point that the character does some form of exercise.
You can also show your character making healthy eating choices as well as unhealthy ones. They can order a salad for lunch or eat ice cream for lunch. Either shows the character’s dietary preferences. These descriptions can be slipped into the work and should be unobtrusive. Such descriptions can server to identify who is talking in dialog thus doing double duty in the work. A sentence or clause here and there is all you need.
If your character has bad health, you need to show that as well. It can be done in a similar way. Your character can take medication in the mornings, or at meals, or before bed. Show it once or twice and that’s all you need to do. You can also show your characters going to physical therapy or moaning about having to do so. Again, you show the character’s health in description of the character, through dialog, or through action.
However you do it, do it sparingly. Remember, your readers have the capacity to process the health of the character they are reading about without having to be constantly reminded of it. Just a mention or two ever so often, depending on the length of the work. In a short story, setting it in a gym with a character working out is enough. Perhaps your character is struggling to do something while others are doing it without a problem can be all that you need to do. Remember to be sparing of the details. Your characters will be more realistic and your readers more engaged.