Vitamins and minerals 101

Everything you need to know about dietary supplements

By Lindsay Borthwick

Vitamins and minerals 101

Headlines trumpet the health benefits of vitamin and mineral supplements, and more than 50 percent of Canadian women profess to take them regularly. Yet research shows that whole foods, with their mix of vitamins, minerals and phytochemicals, outperform supplements in combating disease. Some say that, at best, supplements are an unnecessary “nutritional insurance policy” and, at worst, harmful. So what’s a woman to do? The answer depends on your eating and lifestyle habits, your age and more.

Although most healthy pre-menopausal women can get enough micronutrients (vitamins and minerals the body needs but can’t actually produce) by eating a balanced diet, many Canadian women fall short. “For many food groups, our population is not eating what they’re supposed to,” says Stephanie Atkinson, who helped develop the nutrient-based dietary recommendations for Canada and the United States and who serves as director of the Nutrition and Metabolism Research Laboratory at McMaster University. For example: 72 percent of 31- to 50-year-old women don’t consume the amount of dairy recommended in Canada’s Food Guide, so many don’t get enough calcium.

A well-chosen multivitamin can benefit your health if you’re not eating the recommended servings of foods or avoiding specific food groups, says Atkinson. Those who are pregnant, post-menopausal or following a restricted or vegetarian diet also need to ensure adequate nutrient intake—especially for vitamins D and B12, and folic acid. Atkinson cautions, however, that when it comes to nutrient and multivitamin supplements, more is not always better. Taking more than the upper limit set by Health Canada can actually have harmful side effects.

To clarify the issue, Best Health consulted Health Canada, the U.S. Institute of Medicine, the Dietitians of Canada and other expert sources to come up with a list of the micronutrients adult women aged 31-50 need, and how much. As always, aim to get as many vitamins and minerals as you can from nutrient-dense foods, and check with your doctor before taking any supplements.

The following figures are based on Health Canada’s recommendations for the general adult female population aged 31-50. Women who are pregnant or breastfeeding, smokers, on restrictive diets, over the age of 50, or with certain medical conditions (e.g., anemia) may need different amounts of these vitamins and minerals. (Review the Dietary Reference Intakes for guidelines on all ages and stages.) Note also that manufacturers use various units of measurement for vitamins and minerals. We’ve listed the units most commonly found on product packaging: mg=milligrams; mcg=micrograms; IU=International Unit.

Vitamin A

How much to get daily: 700 mcg (2,333 IU)
Why you need it: Vitamin A refers to several compounds, including retinol, retinal and retinoic acid. Along with provitamins such as beta carotene, it’s important for vision, bone growth, reproduction and cell differentiation. It also helps regulate the immune system.
Where to get it: One seven-inch carrot has 600 mcg. Other food sources: fortified cereals, dark leafy greens, and yellow fruits and vegetables.
Don’t exceed (daily): 3,000 mcg (10,000 IU)
What you need to know: Excess amounts of vitamin A accumulate and can be toxic. Too much can blur vision, cause headaches and vomiting, and also lead to liver, bone and central nervous system problems. Excess retinol can cause birth defects, so multivitamins should contain beta-carotene instead.

Vitamin E

How much to get daily: 15 mg (33 IU)
Why you need it: It’s a powerful antioxidant that protects cells from damage and may guard against chronic disease. Vitamin E also supports immune function, DNA repair and other metabolic processes.
Where to get it: An ounce of almonds (about 23) will provide almost half of your daily needs.
Don’t exceed (daily): 1,000 mg (2,222 IU)
What you need to know: Large doses of vitamin E can thin the blood and may increase stroke risk in people with uncontrolled high blood pressure. It hasn’t actually been proven to protect the heart or prevent cancer. In fact, a recent study linked vitamin E supplements with an increased risk of lung cancer, especially among smokers.

Vitamin C

How much to get daily: 75 mg
Why you need it: This antioxidant vitamin helps the body form collagen in bones, cartilage, muscle and blood vessels, and assists in the absorption of iron.
Where to get it: A glass of OJ will give you almost all the vitamin C you need.
Don’t exceed (daily): 2,000 mg
What you need to know: There is no conclusive evidence that vitamin C supplementation prevents colds, heart disease, cataracts or cancer. Very high doses may lead to gastrointestinal problems.

Folate (Folic acid)

How much to get daily: 400 mcg
Why you need it: It’s a must if you’re breastfeeding, pregnant or trying to conceive; it helps prevent neural tube defects. In fact, the Society of Gynecologists and Obstetricians of Canada now recommends 0.4 to 1 mg (400 to 1000 mcg) per day for women of child-bearing age.
Where to get it: Find it in dark-green leafy vegetables, fortified cereals and whole-grain breads.
Don’t exceed (daily): 1,000 mcg
What you need to know: Folate is essential for women of child-bearing age, but recent studies show no real effect for everyone else against heart disease and depression, and contradictory results for protection against cancer. Low folate levels have been linked to Alzheimer’s, but the connection isn’t conclusive.

Niacin

How much to take daily: 14 mg
Why you need it: Involved in the metabolism of carbohydrates, fats and proteins, niacin also helps normal growth and development.
Where to get it: Stick to meat, fish, poultry, nuts and eggs.
Don’t exceed (daily): 35 mg
What you need to know: This B vitamin can be used to treat high cholesterol, but only under a doctor’s supervision due to the risk of side effects including flushing of the skin and liver damage.

Vitamin D

How much to get daily: 5 mcg (200 IU)
Why you need it: It keeps your bones and teeth healthy by maintaining blood levels of calcium and phosphorus. Vitamin D may help protect against breast, prostate and colon cancers, and decrease the risk of osteoporosis, when combined with a healthy diet and regular exercise.
Where to get it: Sunshine is a major source: Your skin manufactures vitamin D in response to UV light, but the sun’s rays are too weak during Canadian winters to trigger production. Food sources: fortified milk, eggs, fish and fish oils.
Don’t exceed (daily): 50 mcg (2,000 IU)
What you need to know: The Canadian Cancer Society recommends taking 25 mcg for fair-skinned people during the fall and winter and for dark-skinned people all year-round. Exceeding 50 mcg may cause vitamin D toxicity, leading to nausea, vomiting, constipation, weight loss and other symptoms.

Calcium

How much to get daily: 1,000 mg
Why you need it: This mineral helps maintain healthy bones and teeth.
Where to get it: Drink dairy or calcium-fortified beverages. Other food sources: vegetables, canned salmon and sardines, lentils and legumes.
Don’t exceed (daily): 2,500 mg
What you need to know: Many Canadian women don’t get enough calcium from diet alone. If you’re one of them, talk to your healthcare provider about a supplement. Very high doses of calcium can lead to kidney problems, and can also interfere with the absorption of other essential minerals.

Iron

How much to get daily: 18 mg
Why you need it: Iron is a component of many proteins and enzymes that maintain good health, including hemoglobin, which transports oxygen in the bloodstream.
Where to get it: Red meat and poultry are a major source of this mineral. Vegetarians can get iron from fortified cereals, dried beans and dark leafy greens, or a supplement.
Don’t exceed (daily): 45 mg
What you need to know: Only women who are pregnant or have heavy periods, or vegetarians and those with diagnosed deficiencies, such as anemia, need extra amounts of iron. Supplements can interact with medications, other dietary supplements and food, and can worsen conditions like ulcers.

Zinc

How much to get daily: 8 mg
Why you need it: This mineral is important for growth, development and reproduction, and helps maintain healthy immune and nervous systems.
Where to get it: Meat is high in zinc; vegetarians should eat plenty of grains, nuts and dairy products. (Note: Zinc isn’t always added to multi-vitamins.)
Don’t exceed (daily): 40 mg
What you need to know: High doses can interfere with how the body absorbs copper and iron, as well as certain drugs. It may weaken the immune system and also reduce levels of HDL (good) cholesterol. Studies are mixed about zinc's effects on the common cold.

Magnesium

How much to get daily: 320 mg
Why you need it: Essential to metabolism, this mineral also helps to maintain normal muscle and nerve function, to support healthy cardiovascular and immune systems, and to keep bones strong.
Where to get it: Green leafy vegetables, such as spinach, have lots of magnesium. Other sources: some legumes, nuts and seeds, whole grains such as oats, and milk.
Don’t exceed (daily): 350 mg
What you need to know: Too much magnesium from supplements may cause diarrhea, nausea and abdominal cramps.

Beta-carotene

How much to get daily: Not established
Why you need it: Beta-carotene helps maintain eyesight, skin, membranes and immune function. It’s also a powerful antioxidant.
Where to get it: You can get what you need from dark green or orange fruits and vegetables.
Don’t exceed (daily): No upper limit established
What you need to know: Get carotenoids from your diet, rather than supplements, which should be avoided—especially by smokers, who have a greater risk of lung cancer with regular use. Other studies have linked high levels of beta-carotene to higher risks for prostate and lung cancer.

Vitamin B6

How much to get daily: 1.3 mg
Why you need it: This vitamin is involved in the synthesis of brain chemicals and red blood cells, metabolism and maintenance of blood-sugar levels.
Where to get it: Commonly found in fortified cereals, legumes, meat, poultry, fish and some fruits and vegetables.
Don’t exceed (daily): 100 mg
What you need to know: Clinical trials don’t support claims that B6 may reduce carpal tunnel syndrome, PMS depression and heart problems. Also, too much B6 can cause nerve damage.

Vitamin B12

How much to get daily: 2.4 mcg
Why you need it: B12 helps maintain healthy nerve cells and red blood cells. It’s also needed to help make DNA.
Where to get it: Whether you’re a vegetarian or meat eater, fortified cereal can give you all you need. Other sources: fish, meats and dairy.
Don’t exceed (daily): No upper limit established
What you need to know: Some research shows B12 may protect against heart disease, depression and Alzheimer’s, but the evidence isn’t strong. If you’re vegetarian and don’t eat fortified cereals, talk to your doctor about a vitamin supplement.

Thiamine

How much to take daily: 1.1 mg
Why you need it: Nerves and muscles require it. Thiamine also helps the body convert food into energy and supports normal growth.
Where to get it: Reach for fortified or whole-grain products such as rice, bread and ready-to-eat cereals.
Don’t exceed (daily): No upper limit established
What you need to know: There are no known side effects of high doses of thiamine.

Riboflavin

How much to get daily: 1.1 mg
Why you need it: Riboflavin is vital for energy production and vision; it’s also needed for healthy skin and red blood cells.
Where to get it: Milk, eggs, enriched cereals and grains, liver, as well as green vegetables are rich in it.
Don’t exceed (daily): No upper limit established
What you need to know: There are no known side effects of high doses of riboflavin.

Pantothenic acid

How much to take daily: 5 mg
Why you need it: This aids the production of cholesterol and hormones, and the metabolism of carbs, fats and proteins.
Where to get it: It’s found in most plants and animal cells. Meat, potatoes, oats and tomato products are a particularly good source.
Don’t exceed (daily): No upper limit established
What you need to know: There are no demonstrated health benefits from pantothenic acid supplements, which may cause diarrhea if large amounts are ingested.

Selenium

How much to get daily: 55 mcg
Why you need it: Supports thyroid function and the immune system. Selenium is also involved in the synthesis of antioxidant enzymes.
Where to get it: Grab a tuna sandwich or a handful of Brazil nuts. (Note: Selenium isn’t always added to multivitamins, but most North Americans get enough through diet alone.)
Don’t exceed (daily): 400 mcg
What you need to know: One new study suggests that selenium supplementation (200 mcg per day) may increase the risk of developing type 2 diabetes. Exceeding 400 mcg daily may lead to selenium toxicity, symptoms of which include hair and nail brittleness. There is no evidence that selenium supplementation decreases the risk of cancer in women, however one recent study showed it decreased the risk of prostate cancer in men.

Iodine

How much to get daily: 150 mcg
Why you need it: Iodine is needed for the normal thyroid function.
Where to get it: Seafood is rich in it. So is table salt, which is iodized in the United States and Canada (77 mcg of iodine per gram of salt).
Don’t exceed (daily): 1,100 mcg
What you need to know: There is no evidence that iodine supplementation has health benefits for normal, healthy women. However, iodine is important during infancy, so pregnant and breastfeeding women should talk to their health provider about getting enough iodine.

Phosphorus

How much to get daily: 700 mg
Why you need it: Supports the formation of bones and teeth, and is used by all cells in the body.
Where to get it: Meat and milk contain phosphorus.
Don’t exceed (daily): 4,000 mg
What you need to know: Most women get enough phosphorus through diet alone and don’t need to supplement. Very high doses of phosphorus can cause calcium to deposit in certain organs, notably the kidney.

Copper

How much to get daily: 900 mcg
Why you need it: It’s used in the formation of connective tissue and the metabolism of iron.
Where to get it: Seafood, nuts and seeds, wheat bran cereals and whole grains all contain copper.
Don’t exceed (daily): 10,000 mcg
What you need to know: Too much copper can cause gastrointestinal pain, nausea and vomiting, although copper toxicity is very rare.

Biotin

How much to get daily: 30 mcg
Why you need it: It helps the body metabolize carbs, fats and proteins.
Where to get it: Many foods contain some biotin, but liver, egg yolks and yeast are rich sources.
Don’t exceed (daily): No upper limit established
What you need to know: Biotin is not known to be toxic. It’s unclear how much biotin is needed to promote optimal health and prevent chronic disease, so stick to this recommended dose—which is easily achieved through diet alone.

Lutein

How much to get daily: Not established
Why you need it: This plant-derived carotenoid gets concentrated in the lens and retina of the eye.
Where to get it: Darkly coloured vegetables such as kale and spinach, fruits, eggs.
Don’t exceed (daily): No upper limit established
What you need to know: The benefits of lutein, such as protection against age-related macular degeneration and cataracts, are still speculative. But it can’t hurt to get it from power foods such as kale and spinach.

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Best Health Magazine, Summer 2008

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