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Supplements for Health and Fitness
Policosanol
A dietary supplement said to lower cholesterol levels may not work as advertised, a new study shows.
The findings, which appear in the American Journal of Clinical Nutrition, add to evidence doubting the benefits of policosanol, a sugar-cane extract that has become one of the best-selling supplements in the U.S.
A number of studies have suggested that policosanol may be as effective as cholesterol-lowering statin drugs. However, those reports have come mainly from a single research group in Cuba, where policosanol has been popular for 15 years.
In the new study, of 40 adults with mildly elevated cholesterol, North Carolina researchers found that policosanol again failed to outperform a placebo.
Over eight weeks, policosanol users showed no improvements in their levels of "bad" LDL cholesterol or "good" HDL cholesterol compared with placebo users, the study found.
Calcium
Calcium is a mineral found in many foods. Getting enough of this nutrient is important because the human body cannot make it. Even after you are fully grown, adequate calcium intake is important because the body loses calcium every day through the skin, nails, hair, and sweat, as well as through urine and feces. This lost calcium must be replaced daily through the diet. Otherwise, the body takes calcium out of the bones to perform other functions, which makes the bones weaker and more likely to break over time.
Experts recommend that adults get 1,000 to 1,200 mg (milligrams) of calcium each day. Although food is the best source of calcium, most Americans do not get enough of it from food sources. Calcium-fortified foods (like orange juice, bread, cereals, and many others on your grocer’s shelves) and calcium supplements can fill the gap by ensuring that you meet your daily calcium requirement.
The following are strategies and tips to help you meet your calcium needs each day: Use low fat or fat free milk instead of water in recipes such as pancakes, mashed potatoes, pudding and instant, hot breakfast cereals. Blend a fruit smoothie made with low fat or fat free yogurt for a great breakfast.Sprinkle grated low fat or fat free cheese on salad, soup or pasta. Choose low fat or fat free milk instead of carbonated soft drinks. Serve raw fruits and vegetables with a low fat or fat free yogurt based dip. Create a vegetable stir-fry and toss in diced calcium-set tofu. Enjoy a parfait with fruit and low fat or fat free yogurt. Complement your diet with calcium-fortified foods such as certain cereals, orange juice and soy beverages.
Selenium
Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent cellular damage from free radicals. Free radicals are natural by-products of oxygen metabolism that may contribute to the development of chronic diseases such as cancer and heart disease. Other selenoproteins help regulate thyroid function and play a role in the immune system.
What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the world. The content of selenium in food depends on the selenium content of the soil where plants are grown or animals are raised. For example, researchers know that soils in the high plains of northern Nebraska and the Dakotas have very high levels of selenium. People living in those regions generally have the highest selenium intakes in the United States (U.S.) . In the U.S., food distribution patterns across the country help prevent people living in low-selenium geographic areas from having low dietary selenium intakes.
Selenium also can be found in some meats and seafood. Animals that eat grains or plants that were grown in selenium-rich soil have higher levels of selenium in their muscle. In the U.S., meats and bread are common sources of dietary selenium. Some nuts are also sources of selenium.
Selenium content of foods can vary. For example, Brazil nuts may contain as much as 544 micrograms of selenium per ounce. They also may contain far less selenium. It is wise to eat Brazil nuts only occasionally because of their unusually high intake of selenium. Selected food sources of selenium are provided in Table 1.
Table 1: Selected food sources of selenium
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Food
|
Micrograms
(μg)
|
Percent
DV*
|
|
Brazil nuts, dried, unblanched, 1 ounce
|
544
|
780
|
|
Tuna, light, canned in oil, drained, 3 ounces
|
63
|
95
|
|
Beef, cooked, 3½ ounces
|
35
|
50
|
|
Spaghetti w/ meat sauce, frozen entrée, 1 serving
|
34
|
50
|
|
Cod, cooked, 3 ounces
|
32
|
45
|
|
Turkey, light meat, roasted, 3½ ounces
|
32
|
45
|
|
Beef chuck roast, lean only, roasted, 3 ounces
|
23
|
35
|
|
Chicken Breast, meat only, roasted, 3½ ounces
|
20
|
30
|
|
Noodles, enriched, boiled, 1/2 cup
|
17
|
25
|
|
Macaroni, elbow, enriched, boiled, 1/2 cup
|
15
|
20
|
|
Egg, whole, 1 medium
|
14
|
20
|
|
Cottage cheese, low fat 2%, 1/2 cup
|
12
|
15
|
|
Oatmeal, instant, fortified, cooked, 1 cup
|
12
|
15
|
|
Rice, white, enriched, long grain, cooked, 1/2 cup
|
12
|
15
|
|
Rice, brown, long-grained, cooked, 1/2 cup
|
10
|
15
|
|
Bread, enriched, whole wheat, commercially prepared, 1 slice
|
10
|
15
|
|
Walnuts, black, dried, 1 ounce
|
5
|
8
|
|
Bread, enriched, white, commercially prepared, 1 slice
|
4
|
6
|
|
Cheddar cheese, 1 ounce
|
4
|
6
|
What is the recommended dietary intake for selenium?
Recommendations for selenium are provided in the Dietary Reference Intakes developed by the Institute of Medicine. Dietary Reference Intakes (DRIs) is the general term for a set of reference values used for planning and assessing nutrient intake for healthy people. Three important types of reference values included in the DRIs are Recommended Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL). The RDA recommends the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each age and gender group. An AI is set when there is insufficient scientific data available to establish a RDA. AIs meet or exceed the amount needed to maintain a nutritional state of adequacy in nearly all members of a specific age and gender group. The UL, on the other hand, is the maximum daily intake unlikely to result in adverse health effects. Table 2 lists the RDAs for selenium, in micrograms (μg) per day, for children and adults.
Table 2: Recommended Dietary Allowances (RDA) for selenium for children and adults
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Age
(years)
|
Males and Females
(μg/day)
|
Pregnancy
(μg/day)
|
Lactation
(μg/day)
|
|
1-3 y
|
20
|
N/A
|
N/A
|
|
4-8 y
|
30
|
N/A
|
N/A
|
|
9-13 y
|
40
|
N/A
|
N/A
|
|
14-18 y
|
55
|
60
|
70
|
|
19 y +
|
55
|
60
|
70
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There is insufficient information on selenium to establish a RDA for infants. An Adequate Intake (AI) has been established that is based on the amount of selenium consumed by healthy infants who are fed breast milk. Table 3 lists the AIs for selenium, in micrograms (μg) per day, for infants.
Table 2: Adequate Intake for selenium for infants
|
Age
(months)
|
Males and Females
(μg/day)
|
|
0-6 months
|
15
|
|
7-12 months
|
20
|
Results of the National Health and Nutrition Examination Survey (NHANES III-1988-94) indicated that diets of most Americans provide recommended amounts of selenium. The INTERMAP study examined nutrient intakes of almost 5,000 middle-aged men and women in four countries in the late 1990s, including the U.S. The primary aim of the study was to evaluate the effect of dietary micronutrients on blood pressure. Each study participant completed four, 24-hour dietary recalls, during which they were asked to record everything consumed (food, beverages, and dietary supplements) over the previous 24 hours. Selenium intake was lowest among residents of China, the country with the highest known rate of selenium deficiency. Mean dietary intake of selenium of U.S. participants was 153 μg for men and 109 μg for women. Both values exceed the recommended selenium intake for adults and are further evidence of adequate selenium intakes in the U.S..
Who may need supplemental selenium?
In the U.S., most cases of selenium depletion or deficiency are associated with severe gastrointestinal problems, such as Crohn's disease, or with surgical removal of part of the stomach. These and other gastrointestinal disorders can impair selenium absorption. People with acute severe illness who develop inflammation and widespread infection often have decreased levels of selenium in their blood. Physicians will evaluate individuals who have gastrointestinal disease or severe infection for depleted blood levels of selenium to determine the need for supplementation.
People with iodine deficiency may also benefit from selenium supplementation. Iodine deficiency is rare in the U.S., but is still common in developing countries where access to iodine is limited. Researchers believe that selenium deficiency may worsen the effects of iodine deficiency on thyroid function, and that adequate selenium nutritional status may help protect against some of the neurological effects of iodine deficiency. Researchers involved in the Supplementation en Vitamines et Mineraux AntioXydants (SU.VI.MAX) study in France, which was designed to assess the effect of vitamin and mineral supplements on chronic disease risk, evaluated the relationship between goiter and selenium in a subset of this research population. Their findings suggest that selenium supplements may be protective against goiter, which refers to enlargement of the thyroid gland.
As noted above, selenium supplementation during TPN administration is now routine. While specific medical problems such as those described above indicate a need for selenium supplementation, evidence is lacking for recommending selenium supplements for healthy children and adults.
Selenium supplements
Selenium occurs in staple foods such as corn, wheat, and soybean as selenomethionine, the organic selenium analogue of the amino acid methionine. Selenomethionine can be incorporated into body proteins in place of methionine, and serves as a vehicle for selenium storage in organs and tissues. Selenium supplements may also contain sodium selenite and sodium selenate, two inorganic forms of selenium. Selenomethionine is generally considered to be the best absorbed and utilized form of selenium.
Selenium is also available in 'high selenium yeasts', which may contain as much as 1,000 to 2,000 micrograms of selenium per gram. Most of the selenium in these yeasts is in the form of selenomethionine. This form of selenium was used in the large scale cancer prevention trial in 1983, which demonstrated that taking a daily supplement containing 200 micrograms of selenium per day could lower the risk of developing prostate, lung, and colorectal cancer. However, some yeasts may contain inorganic forms of selenium, which are not utilized as well as selenomethionine.
A study conducted in 1995 suggested that the organic forms of selenium increased blood selenium concentration to a greater extent than inorganic forms. However, it did not significantly improve the activity of the selenium-dependent enzyme, glutathione peroxidase. Researchers are continuing to examine the effects of different chemical forms of selenium, but the organic form currently appears to be the best choice.
What are some current issues and controversies about selenium?
Selenium and cancer
Observational studies indicate that death from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher blood levels or intake of selenium. In addition, the incidence of nonmelanoma skin cancer is significantly higher in areas of the United States with low soil selenium content. The effect of selenium supplementation on the recurrence of different types of skin cancers was studied in seven dermatology clinics in the U.S. from 1983 through the early 1990s. Taking a daily supplement containing 200 μg of selenium did not affect recurrence of skin cancer, but significantly reduced the occurrence and death from total cancers. The incidence of prostate cancer, colorectal cancer, and lung cancer was notably lower in the group given selenium supplements.
Research suggests that selenium affects cancer risk in two ways. As an anti-oxidant, selenium can help protect the body from damaging effects of free radicals. Selenium may also prevent or slow tumor growth. Certain breakdown products of selenium are believed to prevent tumor growth by enhancing immune cell activity and suppressing development of blood vessels to the tumor.
However, not all studies have shown a relationship between selenium status and cancer. In 1982, over 60,000 participants of the Nurse's Health Study with no history of cancer submitted toenail clippings for selenium analysis. Toenails are thought to reflect selenium status over the previous year. After three and a half years of data collection, researchers compared toenail selenium levels of nurses with and without cancer. Those nurses with higher levels of selenium in their toenails did not have a reduced risk of cancer.
Two important long-term studies, the SU.VI.MAX study in France and the Selenium and Vitamin E Cancer Prevention Trial (SELECT) study in the U.S., are now underway to further investigate the selenium/cancer prevention link.
The SU.VI.MAX Study is a prevention trial looking at the effects of antioxidant vitamins and minerals on chronic diseases such as cancer and cardiovascular disease. Doses of the nutrients provided in the study are one to three times higher than recommended intakes, including a daily supplement of 100 μg selenium. The SU.VI.MAX study, which began in 1994, has followed more than 12,000 adult men and women. This study was designed to continue for eight years, and the research community is eagerly awaiting the results of this study.
The SELECT study, a long-term study sponsored by the NIH, is investigating whether supplemental selenium and/or vitamin E can decrease the risk of prostate cancer in healthy men. Past evidence as well as pre-clinical trials for the SELECT study suggests that these two nutrients may be effective in preventing prostate cancer. A daily supplement containing 200 μg of selenium will be given to individuals in the selenium-only study group, while men in the combined-nutrients group will receive a daily supplement containing 200 μg selenium and 400 mg vitamin E. The study, which will span from 2001 to 2013, will include 32,400 healthy adult men.
Selenium and heart disease
Some population surveys have suggested an association between lower antioxidant intake and a greater incidence of heart disease. Evidence also suggests that oxidative stress from free radicals, which are natural by-products of oxygen metabolism, may promote heart disease. For example, it is the oxidized form of low-density lipoproteins (LDL, often called "bad" cholesterol) that promotes plaque build-up in coronary arteries. Selenium is one of a group of antioxidants that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease. Currently there is insufficient evidence available to recommend selenium supplements for the prevention of coronary heart disease; however, the SU.VI.MAX study mentioned earlier is looking at the effects of antioxidant nutrients such as selenium on heart disease.
Selenium and arthritis
Surveys indicate that individuals with rheumatoid arthritis, a chronic disease that causes pain, stiffness, swelling, and loss of function in joints, have reduced selenium levels in their blood. In addition, some individuals with arthritis have a low selenium intake.
The body's immune system naturally makes free radicals that can help destroy invading organisms and damaged tissue, but that can also harm healthy tissue . Selenium, as an antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals. Current findings are considered preliminary, and further research is needed before selenium supplements can be recommended for individuals with arthritis.
What is the health risk of too much selenium?
High blood levels of selenium (greater than 100 μg/dL) can result in a condition called selenosis. Symptoms of selenosis include gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage.
Folic Acid
What is folic acid?
Folic acid is a B vitamin. Our bodies use it to make new cells. Everyone needs folic acid. But for women who can get pregnant, it is really important! If a woman has enough folic acid in her body before she is pregnant, it can help prevent major birth defects of her baby’s brain and spine. These birth defects are neural tube defects or NTDs. Women need to take folic acid every day, starting before they are pregnant to help prevent NTDs.
CDC and the U.S. Public Health Service urge every woman who could become pregnant to get 400 micrograms (400 mcg) of synthetic folic acid every day.
How much is enough? Look for 100% DV (Daily Value)
One easy way a woman can be sure she is getting enough folic acid is to take a vitamin that has folic acid in it every day. Folic acid pills and most multivitamins sold in the United States have 100% of the daily value (DV) of folic acid; check the label to be sure. Another way to get enough is to eat a serving of breakfast cereal every day that has been enriched with 100% of the daily value of folic acid. Not every cereal has this amount. Check the label on the side of the box, and look for one that has 100% next to folic acid.
When should a woman start taking folic acid?
These birth defects happen in the first few weeks of pregnancy, often before a woman finds out that she is pregnant. All women should get in the habit of taking folic acid daily even when they are not planning to get pregnant. For folic acid to help, a woman needs to take every day, starting before she becomes pregnant.
Magnesium
Magnesium: What is it?
Magnesium is the fourth most abundant mineral in the body and is essential to good health. Approximately 50% of total body magnesium is found in bone. The other half is found predominantly inside cells of body tissues and organs. Only 1% of magnesium is found in blood, but the body works very hard to keep blood levels of magnesium constant.
Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, supports a healthy immune system, and keeps bones strong. Magnesium also helps regulate blood sugar levels, promotes normal blood pressure, and is known to be involved in energy metabolism and protein synthesis. There is an increased interest in the role of magnesium in preventing and managing disorders such as hypertension, cardiovascular disease, and diabetes. Dietary magnesium is absorbed in the small intestines. Magnesium is excreted through the kidneys.
What foods provide magnesium?
Green vegetables such as spinach are good sources of magnesium because the center of the chlorophyll molecule (which gives green vegetables their color) contains magnesium. Some legumes (beans and peas), nuts and seeds, and whole, unrefined grains are also good sources of magnesium. Refined grains are generally low in magnesium. When white flour is refined and processed, the magnesium-rich germ and bran are removed. Bread made from whole grain wheat flour provides more magnesium than bread made from white refined flour. Tap water can be a source of magnesium, but the amount varies according to the water supply. Water that naturally contains more minerals is described as "hard". "Hard" water contains more magnesium than "soft" water.
Eating a wide variety of legumes, nuts, whole grains, and vegetables will help you meet your daily dietary need for magnesium.
Zinc
Zinc: What is it?
Zinc is an essential mineral that is found in almost every cell. It stimulates the activity of approximately 100 enzymes, which are substances that promote biochemical reactions in your body. Zinc supports a healthy immune system, is needed for wound healing, helps maintain your sense of taste and smell, and is needed for DNA synthesis. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence.
What foods provide zinc?
Zinc is found in a wide variety of foods. Oysters contain more zinc per serving than any other food, but red meat and poultry provide the majority of zinc in the American diet. Other good food sources include beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Zinc absorption is greater from a diet high in animal protein than a diet rich in plant proteins. Phytates, which are found in whole grain breads, cereals, legumes and other products, can decrease zinc absorption.
What is the Recommended Dietary Allowance for zinc?
The latest recommendations for zinc intake are given in the new Dietary Reference Intakes developed by the Institute of Medicine. Dietary Reference Intakes (DRIs) is the umbrella term for a group of reference values used for planning and assessing nutrient intake for healthy people. The Recommended Dietary Allowance (RDA), one of the DRIs, is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals. For infants 0 to 6 months, the DRI is in the form of an Adequate Intake (AI), which is the mean intake of zinc in healthy, breastfed infants. The AI for zinc for infants from 0 through 6 months is 2.0 milligrams (mg) per day.
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