Exercise is the closest thing to a magical pill since it keeps you healthy in so many ways. Aside from helping you drop pounds and look sensational sporting your tightest pants, it keeps your heart healthy, improves your mood and energy levels, keeps sickness at bay, can prevent injuries or alleviate chronic pain, and can even help you have a better night's sleep.
Working out may also help when Aunt Flo comes for her monthly visit. If you suffer from bloating or gut-wrenching cramps (dysmenorrhea) — even though you may not feel up to your normal workout — walking, swimming, or doing another type of light exercise like yoga will improve circulation to relieve painful cramps and ease digestive distress (try these yoga poses that ease cramps). The release of endorphins from exercise is also helpful in getting rid of headaches, fatigue, and your cranky, I-want-to-throw-something-at-everyone mood. Getting your sweat on may also curb your insatiable cravings for junk food and prevent monthly weight gain.
Unfortunately, exercise can also have a negative effect on your period. If you're exercising excessively or obsessively, and have a lower percentage of body weight than is normal for your height (possibly from anorexia), your body could go into rescue mode. Working out takes a ton of energy, so in order for your body to keep up it will begin to shut down unnecessary functions to use what little energy it has to keep your basic life functions going. Since menstruation's main purpose is for reproduction, it is not vital to you and your body will turn off the function to save energy. The good news is that usually when you begin cutting down on the exercise and your body gets the nutrition and calories it needs, your periods should come back. Likewise, if your body fat percentage is much higher than the normal level for your height, periods can also stop.
Exercise and body weight aren't the only things that can affect your cycle, and a missing period isn't a disease, it's a symptom. If you're suffering from irregular or missed periods, make an appointment with your gynecologist so they can help you figure out how to get your period back.