Vitamin Power

Vitamin D

This vitamin is actually a hormone made in the skin. UV rays from sunlight trigger its synthesis. Thus dark-skinned people, those who are rarely outdoors, those living in northern latitudes and older adults must be especially careful to get adequate vitamin D from food or supplements.

Most commonly recognized for its role in bone health, vitamin D is also studied for its possible role in the prevention of many chronic diseases. Studies suggest it can reduce the risk of hip fractures; protect against cancers of the colon, breast, lung and digestive tract; and decrease the inflammation associated with arthritis.

The recommended intake of vitamin D is 200 to 600 IUs (you need more as you get older). Many researchers think it should be much higher. Be careful to stay under 2,000 IUs, the safe upper intake level for adults.

Salmon, tuna canned in oil, sardines canned in oil, fortified milk, egg yolks and fortified cereals are all good sources of vitamin D.

Potassium

Throw a banana in your gym bag and you'll get an instant pick-me-up after a workout. Why? Because bananas are loaded with potassium, crucial for muscle contraction, nerve transmission and fluid balance.

Potassium lessens the risk of developing kidney stones and possibly minimizes bone loss with age. And potassium-rich foods help prevent and treat high blood pressure, which raises your risk of stroke, heart disease and kidney disease. Potassium blunts the effects of excess sodium--75 percent of women take in too much sodium--which causes blood pressure to rise.

The average American woman eats less than half the Institute of Medicine's (IOM) recommended 4,700 milligrams (mg) of potassium each day. Boost your intake by adding sweet potatoes, white potatoes, leafy greens, tomatoes, melons, mangoes, oranges, peaches and yogurt to your diet.

Calcium

Seventy-eight percent of women don't get enough calcium, which is crucial for your health. More than 99 percent of the body's calcium provides structure for your bones and teeth. The remaining calcium goes to the blood and muscles, where it helps the muscles contract, expands and contracts blood vessels, and sends messages through the nervous system. Calcium is so vital that it must be constantly present in blood. When your calcium intake is inadequate, your body steals it from the bones to supply your blood, which can lead to weak bones and osteoporosis.

Researchers have studied calcium's potential role in a variety of illnesses. According to the National Institutes of Health Office of Dietary Supplements, a diet rich in fruits and vegetables and high in calcium reduces blood pressure, lessens the risk of kidney stones (contrary to previous beliefs) and may help fight colon cancer (early research results are promising but inconclusive).

Aim to consume 1,000 to 1,200 mg of calcium daily. Your best sources: milk and other dairy foods, calcium-fortified juices and soymilk, sardines, canned salmon with bones, tofu, leafy greens and canned beans.

If you don't eat dairy products, look at your calcium intake carefully. To get the calcium in 8 ounces of milk, you'll need to eat 8 cups of cooked spinach, 2 1/2 cups of cooked broccoli, 1 1/2 cups of cooked kale or 3 ounces of sardines. If you're not getting enough, you may need to consider supplements.

Calcium supplements are the number one selling mineral supplement, and the two main forms are calcium carbonate and calcium citrate. They are similarly well absorbed for most of us with adequate stomach acid. For those with lower levels of stomach acid--often people with anemia, depression, asthma, osteoporosis and other diseases--calcium citrate is a better choice. Otherwise choose calcium carbonate because it's cheaper, and the pills are smaller. If you need to get more than 500 mg of calcium from supplements, split your dose into no more than 500 mg at a time since absorption decreases as dosage increases. Look for a supplement containing vitamin D, which aids calcium absorption.

Magnesium

This mineral is key to more than 300 enzymes that regulate biochemical reactions throughout the body. You need magnesium to extract energy from food and for normal bone metabolism (50 percent of the body's magnesium is in the bone), muscle and nerve function and blood sugar regulation. And your risk of developing both high blood pressure and diabetes drops as your magnesium intake increases. A recent study in the Journal of Internal Medicine found that for every 100 mg increase in magnesium, the risk of developing type 2 diabetes fell about 15 percent.

The Recommended Dietary Allowances (RDAs) of magnesium for women range from 300 to 360 mg, depending on your age and whether you're pregnant. (You need more when you're expecting.) Get most, if not all, from your diet. Spinach, artichokes and other green vegetables, dried beans, nuts, seeds and whole grains are all good sources. You're advised not to take more than 350 mg from supplements.

Iron

Low iron means low energy. Almost two-thirds of your body's iron is found in hemoglobin, that part of the red blood cell that carries oxygen throughout your body and provides energy. Iron deficiency is most common in women with increased needs for this mineral--teenagers, those with heavy menstrual losses and pregnant women.

Avoid this energy-zapping deficiency by helping your body grab iron from food. Iron in meat proteins, also called heme iron, is well absorbed and largely unaffected by diet. But absorption of nonheme iron (from plants) is hugely influenced by diet. Both meat proteins and vitamin C enhance your body's ability to take in nonheme iron. If you rely on vegetable sources of iron, include vitamin C-rich foods at every meal.

Get iron from liver, beef, oysters, fortified cereals, legumes, lentils and spinach. Aim for 18 mg per day until you reach age 50. Then your needs decrease to only 8 mg. If you don't need extra iron, don't take it. Some evidence suggests that iron stimulates the activity of free radicals, highly reactive molecules capable of causing cell damage.


Jill Weisenberger, M.S., R.D., C.D.E., is a registered dietitian and certified diabetes educator for the Hampton Roads Center for Clinical Research in Norfolk, Virginia.

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