Storing medical ailments in a database
No need to serialize. A relational database (such as MySQL) is intended to store one fact per row. This is the proper way to do it.

Have an Ailments table. It will have 200 rows - one per ailment. This will be used to populate the user's check list.

On save, write each checked ailment to a UserAilment table. It will consist of a foreign key to the user table and a foreign key to Ailments.