A high-quality multivitamin may help avoid micronutrient deficiencies and insufficiencies as a result of suboptimal diet, chronic stress, or particular medications. It’s important to get one that has everything you want and nothing you don’t.
Multivitamins: What You Need to Know
Multivitamins provide many nutrients, vitamins, and minerals that are vital to the human body, and that many do not get through diet alone, even in the US. In fact, many modern diets are surprisingly lacking in vitamins and minerals, which can result in suboptimal micronutrient levels and negatively impact long-term health. A diverse diet that includes plenty of fruits and vegetables, a wide variety of other foods, and does not restrict any specific food group, decreases risk of specific deficiencies and insufficiencies.
More than 50% of Americans take supplements and yet deficiencies and insufficiencies of critical micronutrients abound in our population. Unfortunately, many commonly-available multivitamin brands cut corners by using cheap but ineffective forms of micronutrients that don’t actually provide a nutrient safety net for the people taking them. In our recommendations of specific products, we make sure that they pass a very high bar.
Be sure to look out for the following when choosing your multivitamin:
- Vitamin A should be in the form of beta carotene, rather than retinol, if included
- Vitamin D should be in the form of D3
- Vitamin E should be in the form of d-alpha tocopheryl, if included
- Avoid selenium in the form of sodium selenite
- Choose the more bioactive form of folic acid: methylfolate[7, 8]
- Choose a multivitamin that contains 100% of RDA for vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B12 (cobalamin), and vitamin B9 (methylfolate)
- Choose a product with lower levels of vitamin A and vitamin E
- You may want to take magnesium separately but if it is included, it should not be in the form of magnesium oxide
- You may also want to take calcium separately for better absorption
- Unless you have a known iron deficiency, avoid multivitamins with iron
Vitamins and minerals can affect the absorption and effectiveness of certain drugs, so you should talk to your doctor if you take prescription medications and are considering taking a multivitamin. For example, if you take the anticoagulant warfarin, you may want to avoid multivitamins that contain vitamin K. See more contraindications here.
Conversely, certain drugs may be precisely the reason many people have a specific deficiency or insufficiency. Look up your medicine name in this tool to see if you may be affected.
Certain groups of people should especially consider taking a daily multivitamin, particularly pregnant women, elderly people, smokers, alcoholics, individuals with dietary restrictions such as vegetarians, vegans, and those on low-calorie diets, and people with chronic illnesses who suffer from malabsorption issues. People who are overweight or obese should also consider additional supplementation of fat-soluble vitamins. In particular, postmenopausal women should consider vitamin D and calcium supplementation, which has been shown to increase bone density. Individuals over age 50, those who have difficulty absorbing vitamin B12, and those with vegan or vegetarian diets should make sure that they consume adequate amounts of vitamin B12-fortified foods and possibly consider supplementation.
A multivitamin may not be right for everyone as it’s not a personalized solution and in some cases, it may be better to identify the specific micronutrients in which you are deficient, such as iron, calcium, or vitamin D, and correct for those micronutrients individually. This avoids the risk of under-consuming or over-consuming nutrients through a general multivitamin supplementation. Furthermore, on top of a good multivitamin, you should also consider taking other micronutrients that may benefit long term health. Namely, a good omega-3 supplement, a high-quality magnesium supplement, and in certain circumstances, a separate calcium supplement.
A Closer Look at Multivitamins
Many Americans fall short of the daily intake recommendations for certain vitamins and minerals due to poor diet and minimal consumption of fruits and vegetables. Approximately one-third of Americans take some sort of multivitamin in hopes of filling those nutritional gaps. With the exception of vitamin D, most of the vitamins and minerals in a multivitamin can be obtained by eating a varied diet, which includes adequate amounts of fruits, vegetables, legumes, dairy products, meat, and whole grains.
One complicating issue with multivitamins is that the average American is not equally deficient in all of the various vitamins and minerals typically contained in a multivitamin. Thus, it is likely that most individuals would over-consume certain micronutrients by taking a daily multivitamin. For example, less than 1% of Americans are likely to be deficient in vitamin A, but 6.7% are likely to be deficient in iron, and 10.5 % are likely to be deficient in vitamin B6 (pyridoxine). Age, gender, and dietary habits can significantly increase or decrease an individual’s likelihood of having a particular deficiency. Rather than taking a multivitamin, it may be better to supplement with the specific vitamin or mineral in which you are deficient.
There is no conclusive evidence that taking a multivitamin prevents cancer or heart disease, nor that it increases longevity. A multivitamin is likely to be of benefit only if you are deficient in certain micronutrients. Multivitamins are thought to be beneficial for individuals who regularly consume processed foods and do not get enough essential nutrients from fresh fruits and vegetables.
People that take particular drugs, such as birth control, diabetes medications, and others, as well as those who exercise regularly or are exposed to chronic stress, have different vitamin and mineral needs than the average person. There are also small genetic differences (SNPs) that may result in individual increased or decreased needs for specific nutrients.
If you ultimately decide to take a multivitamin, make sure that the listed amounts of vitamins and minerals do not exceed the Recommended Dietary Allowances (RDA) or Adequate Intakes (AI) published by the National Academy of Medicine. Gender, age, and whether you are pregnant or breastfeeding will have an effect on your RDA/AI for various micronutrients. These amounts are listed on the labels of food products and supplements as %DV, to indicate how much of the Daily Value for each nutrient the product contains.
The approximate daily intake recommendations for vitamins and minerals for adults are listed below. Keep in mind that you are already intaking many vitamins and minerals from your diet, so there is no need for a multivitamin to contain the entire recommended amount of every micronutrient.
|Vitamin C||75-90 mg|
|B1 (thiamin)||1.1-1.2 mg|
|B2 (riboflavin)||1.1-1.4 mg|
|B3 (niacin)||16-18 mg|
|B5 (pantothenic acid)||5 mg|
|B6 (pyrodoxine)||1.3-1.7 mg|
|B7 (biotin)||30 mcg|
|B9 (folate)||400 mcg|
|B12 (cobalamin)||2.4 mcg|
|Vitamin A||700 mcg|
|Vitamin E||15 mg|
|Vitamin D3||2,000 – 5,000 IU|
|Vitamin K||90-120 mcg|
*a multivitamin will only contain 100 mg maximum of potassium
Here is a brief summary of the vitamins and minerals commonly found in multivitamins:
Vitamin C, an important antioxidant, can help synthesize neurotransmitters, heal wounds, and regenerate other antioxidants, such as vitamin E. Adults should aim to get 75-90 mg of vitamin C per day, and no more than 2,000 mg. Fatigue is a common symptom of vitamin C deficiency, and in severe cases, vitamin C deficiency can lead to scurvy. Although most Americans get sufficient amounts of vitamin C from their diet, there are some individuals who are more likely to be deficient. Smokers and those who are regularly exposed to secondhand smoke are more likely to have a vitamin C deficiency, due to the increased oxidative stress caused by smoking tobacco. Elderly people and individuals with restricted diets are also more likely to be deficient in vitamin C.
Fruits, such as oranges and strawberries, and vegetables, such as red pepper, kale, and broccoli, are excellent sources of vitamin C. Different brands of multivitamins vary in their vitamin C content, but many contain at least 100% of the RDA for vitamin C. It is worth noting that long-term intakes of vitamin C above the Tolerable Upper Intake Level (UL) of 2,000 mg per day may increase the risk of adverse health effects, such as gastric discomfort and diarrhea. While vitamin C is best known as an antioxidant, it also has the potential to have pro-oxidant effects and generate harmful free radicals. One study showed that taking 500 mg of vitamin C supplements per day was enough to cause oxidative DNA damage.
Vitamin B1 (thiamin)
Vitamin B1, also known as thiamin, is a water-soluble vitamin that plays an important role in converting nutrients into energy, promoting the healthy growth and development of cells, and maintaining the proper functioning of the cardiovascular and nervous systems. Symptoms of thiamin deficiency include confusion, irritability, muscle weakness, and fatigue, but thiamin deficiency is uncommon in the United States. Adults should intake approximately 1.2 mg of thiamin per day. Fortified breakfast cereals, whole grains, seeds, nuts, legumes, eggs, wheat germ, yeast, soy, pork, fish, and seafood are all good sources of thiamin.
Vitamin B2 (riboflavin)
Vitamin B2, also known as riboflavin, helps convert carbohydrates into energy, promotes a healthy metabolism, and aids in the maintenance of healthy skin. As riboflavin is a water-soluble vitamin, the human body is unable to effectively store it, requiring a daily supply. Beef liver, dairy products, lean meats, green vegetables, fortified breads and cereals, eggs, and yeast are good sources of riboflavin. Individuals who are most at risk for riboflavin deficiency include alcoholics, vegans, and those who are lactose intolerant. Symptoms of riboflavin deficiency include inflammation of the tongue, anxiety, sensitivity to light, hair loss, and skin rash. Adults need roughly 1.1-1.4 mg of riboflavin daily, from food sources and/or supplementation.
Vitamin B3 (niacin)
Vitamin B3, also known as niacin, helps the body convert food into energy and supports the nervous and digestive systems. Niacin also contributes to the function of more than 200 enzymes in the human body. Niacin-rich food sources include organ meats, fish, poultry, milk, eggs, whole grains, nuts, mushrooms, peas, avocados, and other protein-rich foods. As with other B vitamins, alcoholics and vegans are at elevated risk for niacin deficiency, which can cause irritability, loss of appetite, weakness, dizziness, and mental confusion. Niacin deficiency can even be fatal if left untreated. Adults should aim to intake 16-18 mg of niacin per day, but no more than 35 mg.
Vitamin B5 (pantothenic acid)
As with other B vitamins, vitamin B5, also known as pantothenic acid, is needed to convert food into glucose for energy and to maintain healthy skin, hair, and eyes. Vitamin B5 also helps the body to produce red blood cells and cholesterol, as well as important hormones in the adrenal glands. This vitamin helps maintain healthy digestion and nervous system function and is key to the body’s proper use of other vitamins. Vitamin B5 deficiency is rare, but its symptoms include vomiting, fatigue, depression, insomnia, and upper respiratory infections. Adults need about 5 mg of vitamin B5 per day, which can be obtained from foods such as liver, kidney, lean meats, poultry, milk, eggs, yeast, salmon, peanuts, tomatoes, avocados, green vegetables, soybeans, and whole grains.
Vitamin B6 (pyridoxine)
Vitamin B6, also known as pyridoxine, is needed in order to synthesize red blood cells and for the proper function of the immune and nervous systems. It is also key for hormone and hemoglobin production. Symptoms of vitamin B6 deficiency include insomnia, depression, anemia, irritability, muscle twitching, convulsions, confusion, and dermatitis. Those most likely to be vitamin B6-deficient are alcoholics, women who take contraceptives, the elderly, and individuals with thyroid problems. Vitamin B6 deficiency is quite uncommon, whereas excessive intake of vitamin B6, ie. doses of around 200 mg, can lead to irreversible nerve damage. Adults only need about 1.3-1.7 mg per day, even though some multivitamins contain 75 mg or more of vitamin B6. Meat, poultry, liver, fish, shellfish, whole grains such as rice and oats, eggs, legumes, fortified breads and cereals, nuts, fruits, potatoes, and vegetables are all good sources of vitamin B6 and should help people to easily meet the daily intake requirement, without the need for supplementation.
Vitamin B7 (biotin)
Biotin supports the body’s metabolism and helps maintain healthy skin, nails, and hair. It is also important for energy production and the proper function of the nervous, digestive, and cardiovascular systems. Eggs, liver, salmon, avocado, nuts, seeds, legumes, whole grains, and milk are all good sources of biotin. Some people take a biotin supplement in the hopes that it will improve the health and appearance of their hair or nails, but biotin deficiency is quite uncommon, as you only need about 30 mcg of biotin a day. You are unlikely to see results from biotin supplementation unless you had an initial biotin deficiency. Symptoms of biotin deficiency include hair loss, dry or pale skin, dry eyes, anemia, dermatitis, muscle pain, fatigue, nausea, and abnormal heartbeat.
Vitamin B9 (folate/folic acid)
Folate is needed to support fetal development and it plays a critical role in DNA synthesis and repair. Green leafy vegetables, legumes, seeds, orange juice, and liver are all great sources of dietary folate. While dietary folate is found in food, folic acid is a synthetic dietary supplement that can only be found in vitamins or fortified foods. Infants are less likely to born with neural tube defects such as spina bifida or anencephaly if their mothers intake appropriate amounts of folic acid during pregnancy.
Adults need about 400 mcg of folate per day, but pregnant women should aim to get at least 600 mcg, ideally starting at least a month before they become pregnant. However, excessive, long-term consumption of folic acid, ie. above 1,000 mcg per day, can be harmful, leading to tiredness, irritability, confusion, nausea, and other gastrointestinal problems. Excessive folic acid intake can also make it harder to diagnose vitamin B12 deficiency. On the other hand, symptoms of folic acid deficiency include weight loss, fatigue, weakness, and folate-deficiency anemia.
Vitamin B12 (cobalamin)
Vitamin B12, also known as cobalamin, helps the body synthesize red blood cells and contributes to the prevention of megaloblastic anemia. Vitamin B12 deficiency has also been correlated with higher rates of Alzheimer’s disease and osteoporosis. Adults need about 2.4 mcg of vitamin B12 per day. Vitamin B12 is mostly found in animal products, ie. eggs, meat, and dairy, which is why vegans and vegetarians are more at risk for deficiency. In fact, one German study found that 92% of vegan participants in the study had a vitamin B12 deficiency. Fortified non-dairy milks, such as almond milk and soy milk, fortified cereals, and nutritional yeast are all vegan-friendly dietary sources of vitamin B12.
However, one study indicated that 40% of meat eaters in the United States have inadequate levels of vitamin B12, suggesting that even with animal products in their diets, many people are not intaking sufficient amounts of the vitamin from dietary sources. Older people have more difficulty absorbing vitamin B12 because the human body produces less stomach acid as it ages. Vitamin B12 is bound to protein, which requires stomach acid to break down. Other individuals who are at elevated risk for vitamin B12 deficiency include alcoholics, people who have had weight loss surgery, and individuals suffering from atrophic gastritis, pernicious anemia, Crohn’s disease, celiac disease, or lupus. Symptoms of vitamin B12 deficiency include weakness, fatigue, heart palpitations, shortness of breath, pale skin, muscle tingling or weakness, vision loss, depression, and memory loss.
Vitamin A is a fat-soluble antioxidant that promotes healthy vision, helps regulate gene expression, and contributes to building strong bones. Adults need about 700 mcg of vitamin A per day, which can easily be obtained from dietary sources such as carrots, squash, eggs, milk, liver, and leafy green vegetables such as spinach.
Vitamin A exists in two forms. Retinol is the more “active” form and it comes from animal foods. It can be used directly by the body when consumed. The other form of vitamin A, beta carotene, is found in colorful fruits and vegetables, and is ultimately converted into retinol later in the digestion process. Many supplements contain retinol rather than beta carotene because it is more active, but some studies suggest that significant doses of retinol can be toxic, causing more harm than good.[16, 17] Vitamin A deficiency is extremely rare in the United States, so it may be safer to take a multivitamin that omits vitamin A entirely. If your multivitamin does contain vitamin A, make sure that it is in the form of beta carotene. This is because the body simply won’t convert beta carotene into retinol if it doesn’t need it but consuming too much retinol directly as through a supplement could lead to harmful toxicity.
Vitamin E is a fat-soluble antioxidant that is crucial for healthy organ functioning and protecting cells from the damage caused by free radicals. Adults should intake about 15 mg of vitamin E per day. People with digestive disorders and those on very low-fat diets may have a higher risk of vitamin E deficiency. Vegetable oils, green leafy vegetables, fortified cereals, eggs, nuts, and fish are all good sources of vitamin E.
Not only is vitamin E deficiency rare, but the type of synthetic vitamin E found in supplements may actually harm rather than help your body. Some research has shown that long-term intakes of high-dose vitamin E supplements can significantly increase the risk of prostate cancer in men. Another study found that participants who took either synthetic vitamin E or natural vitamin E supplements had an increased risk of death and an increased risk of heart failure; there was an even greater risk among participants who took high-dose supplements. Pregnant women may want to avoid vitamin E supplementation, as some research indicates that this can increase the risk of congenital heart defects in infants. Vitamin E supplements can also interact with blood-thinning medications, which can be fatal in large doses. If you do choose to take a vitamin E supplement or a multivitamin containing vitamin E, always choose the natural form, typically labeled as d-alpha tocopheryl.
Vitamin D2 and Vitamin D3 (cholecalciferol)
Vitamin D plays an important role in calcium and phosphate absorption, helping to keep bones and teeth strong and healthy. It also contributes to the proper function of the immune system, and is thought to help prevent osteoporosis and cancer, and perhaps even type II diabetes. Vitamin D deficiency is fairly common, as many Americans do not get adequate amounts of sun exposure and do not consume enough vitamin D-rich foods. Research suggests that approximately 70% of adults in the United States may have insufficient vitamin D levels for optimal health.
Vitamin D exists in two main forms, D2 and D3, the latter of which is the more biologically-active form. Ideally, vitamin D3 (cholecalciferol) is the form that you should look for in a multivitamin. Fatty fish such as mackerel, tuna, and salmon are the best dietary sources of vitamin D, while beef liver, egg yolks, and cheese contain lesser amounts. Milk, orange juice, soy products, yogurt, and breakfast cereals are also frequently fortified with vitamin D. Adults need at least 600 IU of vitamin D per day, which you can also get through sun exposure, as UVB radiation prompts skin cells to manufacture vitamin D. Short amounts of sun exposure each day in the spring and summer is often sufficient for meeting vitamin D requirements, but this can vary greatly, depending on skin tone, cloud cover, and how much skin is exposed. It is also more difficult to produce enough vitamin D from sun exposure during the winter months. Given the risk of skin damage from sun exposure and the difficulty of obtaining enough vitamin D from food, you may want to take a vitamin D supplement or a multivitamin that contains vitamin D.
Many multivitamins contain at least 1,000 IU of vitamin D, and you may want to take more of this vitamin separately, especially if you are at risk for being deficient or having insufficient levels.[22, 23, 24]
Vitamin K is a fat-soluble vitamin that is stored in the liver and fatty tissue. It plays an important role in the body’s blood clotting ability, as well as contributing to building strong bones and preventing heart disease. Bruising easily, uncontrolled bleeding, heavy menstrual periods, and blood in the urine may all be signs of a vitamin K deficiency. Vitamin K deficiencies are uncommon, but individuals with Crohn’s disease, celiac disease, or alcoholism may be at higher risk for developing a deficiency. Adults need between 90 and 120 mcg of vitamin K per day. Vegetables such as spinach, asparagus, and broccoli, as well as beans, soybeans, eggs, strawberries, and meat are all good food sources of vitamin K.
If you take the drug warfarin (sold under the brand name Coumadin) for heart problems, or if you have a clotting disorder, you may need to watch your diet to control your vitamin K intake, and possibly avoid multivitamins that contain vitamin K altogether.
Potassium is a mineral and electrolyte that plays a critical role in regulating blood pressure, water balance, muscle contractions, nerve impulses, and digestion. Fruits, vegetables, lean meats, whole grains, beans, and nuts are all good sources of potassium.
Potassium deficiency, also known as hypokalemia, is fairly rare, but symptoms include weakness, tingling, nausea, and abdominal cramping. The risk of hypokalemia can be increased by health conditions such as kidney disease, magnesium deficiency, excess sweating, diarrhea, and vomiting. Use of antibiotics and overuse of diuretics can also put you at risk for potassium deficiency.
Conversely, over-consumption of potassium can cause excess amounts to build up in the blood, a condition called hyperkalemia. In some cases, this may cause an irregular heartbeat, also known as cardiac arrhythmia, which can be fatal. Although adults should intake about 4,700 mg per day of potassium, the US Food and Drug Administration (FDA) limits over-the-counter potassium supplements to less than 100 mg per serving due to the potential risks of hyperkalemia. This amounts to just 2% of the daily potassium intake recommendation. Thus, a multivitamin is not an optimal source of potassium, and you may be better off just eating a sweet potato or a banana, which each contain between 400 and 500 mg of potassium, depending on size.
Iodine is an essential mineral that helps the thyroid gland produce hormones needed for fertility, ovulation, and controlling the body’s base metabolic rate. Iodine deficiency can lead to autoimmune diseases, goiter (enlarged thyroid gland), stillbirth, spontaneous abortion, and can potentially increase the risk of prostate, breast, and ovarian cancers. Even a mild iodine deficiency during pregnancy can be dangerous for both mother and baby, leading to high blood pressure for the mother and cretinism for the child, which is a disorder caused by congenital hypothyroidism in which physical and mental growth are severely stunted. Seafood, seaweed, milk, cheese, yogurt, bread, cereal, cranberries, and strawberries are all dietary sources of iodine, but the best and most common source of iodine is iodized salt.
Since the introduction of iodized salt, iodine deficiency has become rare in the United States. Nevertheless, as pregnant and breastfeeding women need 220 mcg and 290 mcg of iodine per day, respectively, which is significantly higher than the requirement for other adults, the American Thyroid Association suggests that pregnant and lactating women should take a multivitamin containing 150 mcg of iodine per day. However, it is worth remembering that the tolerable upper limit for iodine is 1,100 mcg per day, as excess iodine can be harmful and can cause thyroid problems. In some cases, individuals who move from an iodine-deficient country to an iodine-rich country may develop iodine-induced hyperthyroidism, as their thyroid glands have become efficient at using small amounts of iodine.
Selenium is a mineral with antioxidant properties that prevents cellular damage from free radicals, helps support a strong immune system, and regulates thyroid function. Brazil nuts are packed with selenium, with just one nut more than fulfilling the Recommended Daily Allowance. Selenium can also be obtained from dietary sources such as bread, brewer’s yeast, wheat germ, whole grains, fish, lean meats, poultry, legumes, nuts, garlic, sunflower seeds, and eggs.
Symptoms of selenium deficiency include fatigue, hypothyroidism, slow mental processing, and possibly recurrent miscarriages. However, selenium deficiency is very rare, and those at risk typically have a gastrointestinal disorder such as Crohn’s disease, are on kidney dialysis, or are HIV-positive. In reality, selenosis (chronic high selenium intake) is more of a concern than selenium deficiency. Symptoms of selenosis include hair and nail loss or brittleness. Other symptoms include nausea, diarrhea, skin rashes or lesions, nervous system abnormalities, mottled teeth, fatigue, and irritability. Brazil nuts can cause selenium toxicity if consumed regularly and in large quantities.
Women should intake about 55 mcg of selenium per day, while men should intake 70 mcg. Pregnant women should try to intake 65 mcg daily. Vitamin E and selenium facilitate each other’s absorption, so they should ideally be taken together. Avoid supplements and multivitamins containing inorganic forms of selenium, such as sodium selenite, as they may cause adverse interactions with vitamin C and other nutrients.
Zinc is an essential mineral that promotes hormone production, improves immunity, facilitates digestion, and acts as an anti-inflammatory agent. Adults need about 8-11 mg per day of zinc. Oysters are the best source of dietary zinc, but, beef, pork, crab, dairy products, beans, peas, lentils, seeds, nuts, and fortified breakfast cereals also contain significant amounts of zinc. Zinc deficiency is rare in the United States, but those most at risk are people with gastrointestinal issues, vegetarians, pregnant women, and alcoholics. Zinc deficiency symptoms include thinning hair and hair loss, skin problems, impaired immune function, diarrhea, appetite loss, vision problems, psychological and behavioral problems, delayed growth, and impotence.
Older adults may also be at risk for zinc deficiency, according to one study that found that 35%–45% of adults aged 60 years or older had zinc intakes below the average requirement for their age group. However, it is important not to exceed the upper intake limit for zinc, which is 40 mg per day for adults. Furthermore, very large doses of zinc, ie. 150–450 mg per day, have been correlated with severe side effects, such as interfering with the body’s metabolism and absorption of minerals such as copper, iron, and magnesium. Excessive zinc intake can also impair the immune system and can result in low levels of high-density lipoproteins.
Calcium is an essential mineral that aids in the building of bones, helps with blood clotting, and facilitates nerve impulse transmission. Almost all of the calcium in your body is stored in your bones and teeth.
Although adults need 1,000 mg of calcium per day, many Americans fall short of this recommended amount, which can lead to net bone loss, reduced bone density (osteopenia), and, ultimately, osteoporosis. Older individuals (especially post-menopausal women) and pregnant women require additional calcium. Spinach, kale, soybeans, white beans, cheese, milk, fish, and fortified juices and cereals are all good sources of calcium.
Calcium is optimally absorbed when taken in doses of no more than 500-600 mg, so you should try to intake calcium from foods and/or supplements in relatively small amounts throughout the day. Stomach acid helps the body to absorb calcium, meaning that calcium supplements are best absorbed along with food. Most multivitamins do not contain sufficient calcium to meet daily intake recommendations, so if you are worried about your calcium intake, consider taking an additional supplement. Try starting with a 200-300 mg calcium supplement, and then gradually increase the amount, if needed. However, it is important not to exceed the upper limit of 2,000-2,500 mg of calcium daily.
Magnesium is a mineral that is crucial for normalizing blood pressure, maintaining strong bones and healthy muscles, and ensuring proper nerve function. Green leafy vegetables such as spinach, legumes, nuts, seeds, whole grains, and fortified breakfast cereals are good dietary sources of magnesium. Adults need 300-400 mg of magnesium per day, although pregnant women should intake at least 350 mg per day.
It is likely that many Americans are not meeting the daily magnesium requirements through diet alone. Men aged 71 years and older and adolescent females are most at risk for having low magnesium intakes. Alcoholics, diabetics, and individuals with celiac disease or gastrointestinal diseases such as Crohn’s disease also have a higher risk of magnesium deficiency, which is characterized by symptoms such as vomiting, fatigue, weakness, nausea, and loss of appetite. Zinc supplements can potentially interfere with magnesium absorption, possibly resulting in magnesium deficiency.
Manganese, which should not be confused with magnesium, plays a role in fat metabolism, calcium absorption, and helps form connective tissue, bones, and hormones. Dietary sources of manganese include whole grains, fruits, nuts, and seeds. Adults need 1.8-2.3 mg of manganese per day, although pregnant women should intake at least 2 mg daily.
Although an estimated 37 percent of Americans do not meet this recommendation for manganese intake, manganese deficiency is very uncommon. Deficiency usually only occurs if there is another factor that interferes with absorption, such as excessive sweating, taking oral contraceptives or antacids, intaking excess iron, copper, calcium or magnesium, or having a chronic disorder of the liver or gallbladder. Symptoms of manganese deficiency include metabolism and appetite changes, seizures, dizziness, weakness, nausea, vomiting, weakened immune function, iron-deficiency anemia, and brittle hair and nails. Low levels of manganese have also been linked to infertility, joint pain, and brittle bones.
As previously mentioned, supplementation with certain other minerals can interfere with the body’s absorption of manganese. In one study, taking an iron supplement (60 mg/day for four months) was linked with decreased blood manganese levels. Conversely, other research has shown that iron deficiency can increase the risk of manganese accumulation in the brain. Taking supplemental magnesium and calcium can interfere with manganese bioavailability in otherwise healthy adults.
In reality, manganese deficiency is fairly uncommon. However, overconsumption of manganese can be harmful. For example, abnormally high concentrations of manganese are associated with neurological disorders and poor cognitive performance in schoolchildren. The tolerable upper limit for adults is 11 mg of manganese per day, which should not be exceeded.
Most of the iron in the human body functions as a component of hemoglobin, a protein molecule found in red blood cells that carries oxygen from the lungs to the rest of the body. Iron is also an important component of myoglobin, a protein that provides oxygen to muscle cells. Iron is essential for maintaining healthy skin, nails, and hair. Mild forms of iron deficiency can lead to fatigue and can affect cognitive development, while more severe forms can lead to iron-deficiency anemia, which occurs when the body does not produce sufficient quantities of red blood cells. Symptoms of iron deficiency include fatigue, weakness, dizziness, rapid heartbeat, pale skin, cramps, and difficulty concentrating. Iron deficiency during pregnancy is associated with preterm birth, low birth weight, and infant mortality.
The best dietary sources of iron include beef, liver, poultry, and seafood, although eggs yolks, fortified breakfast cereals, grains, nuts, seeds, beans, fruits, and vegetables also contain iron. Most Americans get enough iron from food sources, but vegetarians, adolescent women, and pregnant women may need to take an iron supplement.
All adults should intake 8-18 mg of iron each day, while pregnant women need about 27 mg. Ideally, for maximum absorption, an iron supplement should be taken on an empty stomach, or with a very small amount of food if taking the supplement by itself causes nausea. Additionally, experts advise that you should not take an iron supplement within one to two hours of consuming foods containing calcium, manganese, tin, or zinc, due to absorption issues. This means that it may be better to take a separate iron supplement than to take a multivitamin containing iron. For adults, the tolerable upper limit for daily iron intake is 45 mg.
Proper Dosage and Contraindications
It is widely recommended that pregnant women take a daily multivitamin due to the elevated prenatal requirements for folic acid, iron, calcium, and other nutrients. Frequently, elderly people and vegetarians are at risk for nutrient deficiencies due to changes in metabolism and dietary restrictions, respectively. If you are restricting your food intake in order to lose weight or for other health reasons; if you avoid eggs, dairy or wheat due to intolerances; if you follow a plant-based diet and avoid meat and other animal products; or if you are over the age of 50, you may want to consider taking a multivitamin.
However, for people who do not belong to one of these demographic groups or have specific micronutrient needs that are not being met, there is no conclusive evidence that taking a multivitamin is beneficial or necessary. In fact, given their popularity, the medical literature on multivitamins is surprisingly sparse.
Although multivitamins have been shown to improve overall nutrition in the elderly, there is no conclusive evidence that they prevent any chronic diseases. However, multivitamins may have a positive impact on cancer prevention in demographics with suboptimal nutrition. Multivitamins, especially those containing antioxidants, may also slow the progression of age-related macular degeneration in the elderly and vision loss in those over age 50.[34, 35]
The overarching issue with multivitamins is that they are not necessarily formulated to address the most pressing health concerns of the U.S. population. Generally, most people could benefit from a multivitamin containing higher amounts of vitamin E, potassium, and calcium, but with lower amounts of vitamin A, iron, and niacin. One study of people who took a daily multivitamin found that three-quarters of the participants already had adequate micronutrient intakes from food alone, while multivitamin supplementation increased their intakes of micronutrients by about eight percent. In the study, multivitamins improved intakes of vitamin E and zinc, but also caused potentially excessive intakes of vitamin A, iron, and niacin. However, this effect may also have been due to the study using suboptimal multivitamin formulations.
There are many multivitamins marketed at children. Make sure that if you are choosing a supplement for your child, that it is properly formulated to include nutrients that your child may not be getting enough of and not too much of other nutrients that he or she is already getting from their diet. Supplements can push some nutrient intakes past the daily recommended amount, which is why some experts do not recommend any type of multivitamin supplementation for children. Read more about children’s multivitamins here.
Some research has pointed to potential dangers associated with multivitamin supplementation. According to one Swedish study, there may be a correlation between multivitamin use and an increased breast cancer risk. And as previously mentioned, another study found a link between regular vitamin E supplementation and an increased risk of prostate cancer in men. Another study showed that postmenopausal women who took a daily multivitamin had a slight but significant increase in overall mortality risk when compared to those who did not take a multivitamin. However, all of these studies deal with correlation, not necessarily causation, and there are many other factors that could have contributed to the increased risks for cancer and other diseases among certain study participants. In other words, there is little evidence that multivitamin intakes contributed directly to higher incidences of these illnesses. Furthermore, as healthy individuals are also more likely to take a multivitamin, it is difficult to attribute any specific health benefits to multivitamins alone.
Some studies have identified a potential link between beta-carotene, a natural precursor to vitamin A, and increased risk of lung cancer among smokers and former smokers. Pregnant women should also avoid excess vitamin A in the form of retinol, as this may increase the risk of birth defects. Postmenopausal women should avoid multivitamins that contain large amounts of iron, as they require less iron than other demographics. Additionally, individuals who take any type of blood-clotting medication, such as warfarin (Coumadin), should avoid multivitamins containing vitamin K.
Another potential issue with multivitamins is that, in large quantities, certain vitamins and minerals may compete with one another, reducing their absorption. For example, large doses of calcium can interfere with the absorption of other minerals, which is why a calcium supplement should be taken at a different time of the day than other supplements. Large doses of magnesium can also interfere with the absorption of other micronutrients. There is some evidence that in large doses, the absorption of fat-soluble vitamins (ie. vitamins A, D, E, and K) may be reduced when they are taken simultaneously, due to competition. Thus, a multivitamin that contains large quantities of fat-soluble vitamins may not be as effective as taking each vitamin separately, at different times of the day.
Vitamins and minerals can also affect the absorption and effectiveness of certain medications. It is always a good idea to talk to your doctor before beginning any kind of supplementation, even with an over-the-counter product, if you are already taking other medications.
Choosing the Right Multivitamin
If you do decide to take a multivitamin, try to choose one that falls within the daily intake recommendations for vitamins and minerals. Many multivitamins contain 100% or more of the daily recommendations for certain micronutrients, but more is not necessarily better. If you consume a wide range of nutrient-rich foods, especially fortified foods, and also take a daily multivitamin, you may actually exceed the tolerable upper limit for certain vitamins and minerals, thus increasing the likelihood that you will experience adverse side effects. Try to find a multivitamin that contains 100 percent of the Daily Value for vitamins D, B1 (thiamin), B2 (riboflavin), B3 (niacin), B12 (cobalamin), and B9 (folic acid), but look for one that contains lower levels of vitamin A and vitamin E.
When choosing a multivitamin, make sure that it contains vitamin E in its most active and natural form, d-alpha tocopheryl, rather than the synthetic form, dl-alpha tocopheryl. Ideally, your multivitamin will also contain vitamin D in the form of D3, as it is more biologically active than D2. Ensuring you’re getting enough vitamin D is also important and you may want to take this vitamin separately to get a high-enough dose. New research shows that previous RDA was grossly understated and best outcomes occur when people consume between 2,000 IU and 5,000 IU of vitamin D per day. Be sure to check the expiration date on all packaging, as supplements nearing their expiration date contain lower levels of nutrients due to natural degradation.
Given that some studies have suggested a link between multivitamin supplementation and an increased risk of cancer and overall mortality, you may be better off consuming a wide range of fruits and vegetables than relying on a multivitamin to meet your micronutrient needs. Rather than taking a multivitamin, if you have a specific vitamin or mineral deficiency, you can take a specialized supplement, thus eliminating the danger of over-consuming other nutrients. For example, postmenopausal women should definitely consider taking vitamin D and calcium supplements, which have been shown to increase bone density. Likewise, individuals over age 50, as well as vegans and vegetarians, should make sure that they consume enough vitamin B12-fortified foods and/or consider a vitamin B12 supplement.
Make sure your multivitamin is made by a high-quality manufacturer following GMP using high-quality source inputs, like the ones recommended here.