context: You've heard that calcium protects your bones and that your glass of milk is loaded with it, but what do you really know about this essential nutrient? Most people may not realize that calcium is the most abundant mineral in the body. Or that calcium does far more than just strengthen your bones and teeth. Here's a quick primer on calcium -- including why you need it and where to get it. Calcium is probably best known for strengthening bones and teeth. In fact, most of the calcium in our bodies is stored in the bones and teeth. As bones undergo their regular process of breakdown and remodeling, calcium helps build new bone, especially during growth and development. Getting enough calcium is important for keeping your bones strong throughout your lifetime, but especially during childhood, while the bones are still growing. It's also essential during the senior years, when bones start to break down faster than they can rebuild. Older bones become more brittle and easily fractured -- a condition called osteoporosis. Calcium also plays an important role in several other body functions, including: Nerve signal transmission Hormone release Muscle contraction Blood vessel function Blood clotting There's also some early evidence that calcium might lower blood pressure and help protect against colorectal and prostate cancers. However, these benefits have yet to be confirmed in studies. How much calcium you need depends on your age and gender. The recommended daily dietary allowances for calcium are: Age Male Female 1-3 years 700 mg 700 mg 4-8 years 1,000 mg 1,000 mg 9-13 years 1,300 mg 1,300 mg 14-18 years 1,300 mg 1,300 mg 19-50 years 1,000 mg 1,000 mg 51-70 years 1,000 mg 1,200 mg 71+ years 1,200 mg 1,200 mg Getting much more than the recommended amount of calcium from food and supplements increases the risk of side effects, so it's best to avoid taking too much. The ideal way to get calcium, like any nutrient, is from foods. Dairy products such as milk, cheese, and yogurt are the best and most obvious sources. One 8-ounce cup of low-fat, plain yogurt contains 415 mg of calcium -- more than a third of the daily recommendation for most age groups. An 8-ounce glass of nonfat milk will provide you nearly 300 mg of calcium. And 1.5 ounces of part-skim mozzarella has 333 mg. Even if you're lactose intolerant, you can still enjoy your milk by choosing one of the lactose-free or lactose-reduced dairy products available at your local supermarket. Another option is to take lactase enzyme drops or tablets before you eat dairy. Some studies show many people can tolerate dairy if they choose low lactose foods like hard cheeses, eat lactose containing foods and beverages in small amounts. or add dairy as an ingredient in a meal. Since dairy is the best source of calcium, it's worth experimenting by adding small amounts to your diet to see what you can tolerate. Several non-dairy foods are also good sources of calcium, including: Food Calcium content per serving Calcium-fortified orange juice, 6 ounces 375 mg Canned sardines with bones, 3 ounces 325 mg Firm tofu made with calcium sulfate, 1/2 cup 253 mg Canned salmon with bone, 3 ounces 181 mg Calcium-fortified breakfast cereal, 1 cup 100-1,000 mg Boiled turnip greens, 1/2 cup 99 mg Cooked fresh kale, 1 cup 94 mg If you're not getting enough calcium from food alone, your doctor might recommend a supplement. Calcium supplements come in two main forms: Calcium carbonate -- found in products such as Caltrate 600, Os- Cal 500, Viactiv Calcium Chews, and store brands Calcium citrate -- found in supplements such as Citracal Calcium carbonate is also commonly found in over-the-counter antacids, such as Rolaids and Tums. You need to take calcium carbonate with food, because it's easier for your body to absorb that way. You can take calcium citrate on an empty stomach or with food. To maximize your absorption of calcium, take no more than 500 mg at a time. You might take one 500 mg supplement in the morning and another at night. If you take a supplement that also contains vitamin D, it will help your body absorb calcium more efficiently. Avoid eating these foods when you take your supplement, because they can interfere with calcium absorption: Caffeinated coffee and soda High-salt foods Before taking calcium supplements, you need to be aware of the side effects of high calcium intake, which include: Constipation Gas or bloating Risk of kidney stones Calcium can also decrease absorption of some medications, including osteoporosis medicines, thyroid medicines, and some antibiotics. Ask your doctor if your medicines may interact with calcium, or to be safe, just don't take them at the same time. Taking calcium and vitamin D supplements with thiazide diuretics may increase the chance of kidney stones. A June 2012 study in the journal Heartalso linked calcium supplements with a greater likelihood of heart attacks. This finding may be of special concern to anyone who is already at risk for heart disease. Experts disagree regarding who should take calcium and vitamin D supplements. The U. S. Preventive Services Task Force doesn't recommend taking calcium supplements to prevent osteoporosis-related fractures in postmenopausal women, because there isn't enough evidence to support a benefit. Other organizations, including the National Osteoporosis Foundation and the Institute of Medicine, recommend supplements if you're not meeting your daily calcium requirements with diet alone. Although your bones need calcium, don't take any supplements without first talking to your doctor. Find out which form of calcium is best for you to take, how much you need each day, and what to do if you experience any side effects.