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Doing so helps keep your bones strong, which may help reduce your chances of a stress fracture in the future. For women under 50 and men under 70, you need 1,000 milligrams of calcium a day; after that, you need 1,200 milligrams. Dairy products are a good source of calcium, particularly ones fortified with vitamin D, which aids your calcium absorption.  Fortified orange juice, fortified tofu, canned salmon (with the bones), kale and other greens, and sardines are all good sources of calcium.  Vitamin D is mainly found in fatty fish, such as mackerel, tuna, and salmon, as well as fortified foods like cereal, juices, and milk. You can also get vitamin D from sunlight on your skin, but going outside without sunscreen can put you at risk for sun cancers. Supplements are also an option, but always talk to your doctor first. If you're under 50, you need 400-800 IUs per day or 800-1,000 if you're over 50. Running on inconsistent surfaces like sand or even grass can set you up for an injury. Sloping, holes, and surfaces that change from hard to soft make your body work harder and can lead to injuries like stress fractures. Opt for a running track when you can. Running shoes absorb some of the shock of your feet hitting the ground, which helps relieve the pressure that could cause stress fractures. Make sure your shoes fit well and are made specifically for running. Go to a store to be fitted the first time you buy shoes; after that, you can purchase them online if you prefer. Make sure to change your shoes out every 250 to 500 miles (400 to 800 km) of use. If you notice your shoes have lost much of their "bounce," it's time to change them out. If you always run for your exercise, you get repeated impacts on the same part of your legs. Instead, choose lower-impact activities for part of your exercise, which will help take the pressure off. For instance, try swimming or bicycling. Strength training helps build up your muscles, which in turn provide support for your bones. With stronger muscles, you're less likely to get a stress fracture. Strength training involves using your body weight, resistance bands, or free weights to slowly build up your muscles through resistance. Pushups, situps, squats, lunges, and chest presses are all examples of strength training.

Summary:
Ensure you're getting enough vitamin D and calcium in your diet. Run on a smooth, somewhat soft surface like a track. Purchase good running shoes. Include cross-training in your routine. Make strength training a part of your workout.