This is a short question that requires a long answer!
Generally, gums recede because of poor oral hygiene, degenerative diseases, poor nutrition, clenching and or grinding your teeth, poor occlusion (the way your teeth come together) and / or a combination of all these. Stress plays a huge role in this. Stress can cause degeneration. By saying this I mean that it can lower your immune system, which can result in your gums reacting more to plaque (the bacterial film that accumulates on your teeth until it is removed). Your repair mechanisms become compromised. People tend to clench more at their jobs, in thought, or in their sleep when they are under stress. Ways to care for your gums include impeccable home care. Brush your teeth thoroughly with a soft tooth brush and floss them. Getting correct instructions on how to brush and floss is important. Your hygienist should show you how to do this and actually have you do it while you are at the office. I know people who spend a great deal of time on their teeth yet they are not effective. Getting correct instructions is a must. Being able to duplicate the technique is imperative. Practice, practice, practice while you have your coach present! Vitamins like B complex and Vitamin C are important. A muscle relaxing splint similar to a night guard can be very helpful to take the “load” of your teeth at night when you uncontrollably clench and grind. This is an appliance that your general dentist can make for you. I do not advise you to purchase a night guard over the counter as they are soft and you will still clench on them. You may take the load of your teeth, but you increase the load on your jaw joint with these over the counter appliances. Regular professional cleanings are also essential. Keep in mind that even having your teeth cleaned twice a year may not be enough to control your inflammation. It takes about 90 days for the micro organisms to multiply sufficiently to cause tissue breakdown in deep pockets. Deep pockets are the spaces between your tooth and your gum that are 4 or more millimeters deep. Your hygienist or dentist will measure your pockets to see if any 4 mm. spaces exist. If so they will recommend that you get a professional treatment about every 90 days or 3 months. If you learn and practice these recommendations it can be easy and rewarding. Bleeding gums are the easiest way for bacteria to get into your blood stream, and play havoc to your health. It is worth your while to learn how to care for your teeth and gums, and this will extend your life!
This may be information overload. Hopefully it is helpful. Thanks for your questions.