Also: New mammography guidelines. Best source of vitamins?

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What you should know about magnesium Image: Bigstock You need magnesium for many tasks. It's involved in more than 300 chemical reactions in the body. Muscles need this mineral to contract; nerves need it to send and receive messages. It keeps your heart beating steadily and your immune system strong. Most people can get enough magnesium by eating foods such as green leafy vegetables, whole grains, beans, nuts, and fish. Magnesium supplements are sometimes marketed as "super-pills" that can fix a long list of ailments such as muscle tension, low energy, and trouble sleeping. But think twice before you reach for a magnesium supplement. Dr. Bruce Bistrian, chief of clinical nutrition at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School, says magnesium deficiency is very rare. "The kidney has an extraordinary ability to reduce magnesium loss in urine, and thus achieve magnesium balance on a wide variety of intakes," he explains. For people who have trouble absorbing magnesium from food — such as those with celiac disease, kidney problems, alcoholism, or chronic digestive problems — supplements can be useful. Medicines (including some "water pills" and antibiotics) can also interfere with magnesium absorption, making a supplement necessary. But what about the claims that magnesium supplements can improve energy, sleep cycles, and body aches? Dr. Bistrian is skeptical. "There's no evidence to my knowledge that it would be effective for those symptoms," he says. If you're concerned about low magnesium, ask your doctor for a blood test. To maintain a healthy magnesium level, it's best to get this mineral from food, especially high-fiber foods such as dark green leafy vegetables, unrefined grains, and beans. The recommended dietary allowance (RDA) of magnesium from food is 420 milligrams (mg) per day for men ages 50 and older. The RDA of magnesium from supplements is lower: 350 mg per day for men and women. Magnesium-rich foods 1 ounce of dry roasted almonds 80 milligrams 1/2 cup frozen spinach (cooked) 78 milligrams 3/4 cup bran flakes 64 milligrams 1 medium baked potato, with skin 48 milligrams 1/2 cup canned kidney beans 35 milligrams For more on magnesium and other nutrients that can keep you healthy, buy Making Sense of Vitamins and Minerals, a Special Health Report from Harvard Medical School. Share this story: News and Views from the Harvard Health Blog New mammography guidelines call for starting later and screening less often Women can wait until age 45 to start getting annual mammograms and cut back to every other year once they turn 55, according to new breast cancer screening guidelines from the American Cancer Society. Best source of vitamins? Your plate, not your medicine cabinet Image: iStock Vitamin and mineral supplements from a bottle simply can't match all the biologically active compounds teeming in a well-stocked pantry. By focusing on the big picture, it's easy to get plenty of the vitamins, minerals, and other micronutrients you need to keep you healthy and prevent disease. Here are some tips. Fiber. It's the part of plant foods that we can't digest. Eating foods high in fiber helps reduce total and LDL ("bad") cholesterol, improve blood sugar control, and prevent constipation. High-fiber foods also help with weight loss by making you feel full. There are lots of high-fiber foods to choose from: brown rice bulgur (cracked wheat) barley oats nuts beans and lentils apples blueberries carrots Vitamins and minerals. Vitamins are organic substances found in plants and animals. Minerals are inorganic elements from the earth (soil and water). Both are essential for normal growth and optimal health. Here's a list of vitamins and minerals that are crucial for good health, plus the best food sources of each: iron — meat, poultry, fish, and beans vitamin A — carrots, sweet potatoes, spinach, kale vitamin B12 — meat, poultry, fish vitamin E — nuts, seeds, vegetable oils Phytochemicals. Phytochemicals are chemicals made by plants. They are not essential to life, but they do have a positive effect on health. Diets rich in phytochemicals have been associated with a lower risk of chronic diseases, such as cancer and heart disease. They are found in fruits, vegetables, beans, and grains. The following is a list of key phytochemicals, plus the best food sources of each. flavonoids — blueberries, raspberries, strawberries, blackberries carotenoids — orange vegetables such as carrots, sweet potatoes, and winter squash lycopene — tomatoes isoflavones — soy foods, such as soybeans (or edamame) resveratrol — red grapes catechins — teas Be creative Adding finely grated carrots or zucchini to pasta sauce, meat loaf, chili, or a stew is one way to get an extra serving of vegetables. Dip vegetables into hummus or another bean spread, some spiced yogurt, or even a bit of ranch dressing. Slather peanut butter on a banana or slices of apple. Try mashed avocado as a dip with diced tomatoes and onions, or as a sandwich spread, topped with spinach leaves, tomatoes, and a slice of cheese. To learn more ways to ensure that you get the vitamins and minerals your body needs, buy Making Sense of Vitamins and Minerals, a Special Health Report from Harvard Medical School. Share this story: Featured in this issue Making Sense of Vitamins and Minerals Featured content: • Vitamins and minerals: The basics • Federal guidelines • Making sense of scientific studies • Cast of characters: From vitamin A to zinc • SPECIAL BONUS SECTION: Does your diet deliver the daily recommended dose? •  ... and more! Click here to read more » Harvard Medical School offers special reports on over 50 health topics. Visit our website at http://www.health.harvard.edu to find reports of interest to you and your family. PHONE ORDERS - please call our toll-free number: 1-877-649-9457. You are currently subscribed to HEALTHbeat as dr.samah.saied.ahmed@gmail.com. UNSUBSCRIBE SUBSCRIBE TO HEALTHbeat VIEW HEALTHbeat ARCHIVES PRIVACY POLICY Visit our website at: www.health.harvard.edu Email us at: healthbeat@health.harvard.edu FOLLOW US ON:  Facebook Twitter Copyright © 2015 by Harvard University. Harvard Health Publications, 10 Shattuck Street, 2nd Floor, Boston, MA 02115, USA * Please note, we do not provide responses to personal medical concerns, nor can we supply related medical information other than what is available in our print products or website. For specific, personalized medical advice we encourage you to contact your physician.