In This ArticleView AllIn This ArticleThe Different Types of Supplements and How They’re AbsorbedCan Taking Large Amounts of Supplements Cause Toxicity?How to Safely Take SupplementsFAQs
In This ArticleView All
View All
In This Article
The Different Types of Supplements and How They’re Absorbed
Can Taking Large Amounts of Supplements Cause Toxicity?
How to Safely Take Supplements
FAQs
If you’re like a lot of Americans, you probably have a medicine cabinet full of vitamin and mineral supplements aimed at helping you meet your nutrient needs and boost your health. And they can often fill in any deficiencies in your diet. But taking large doses of some of them—particularly over a long period of time—is not the answer. In fact, certain vitamins and minerals can be toxic when taken in excess.
Vitamins and minerals, also referred to as micronutrients, are essential in small quantities to sustain normal cellular and molecular functions in the body. Achieving your nutrient intake through diet is a first-line approach. However, theAcademy of Nutrition and Dieteticsacknowledges that there are some instances when you may need supplemental support, such as during times of growth, pregnancy, lactation and aging.
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Most essential vitamins are water-soluble—with the exception of vitamins A, D, E and K. The latter are fat-soluble; they need fat for absorption and can be stored in body tissues. Water-soluble vitamins are used when they are digested and typically do not stay in your system for long periods of time. Anything ingested in excess of what your body needs is excreted through your urine.
Taking large doses of fat-soluble supplements is more likely to cause toxic effects. However, megadoses of certain water-soluble vitamins and minerals can also lead to hypervitaminosis (the medical term for vitamin toxicity).
Yes. That’s why theFood and Nutrition Board of the National Academies of Sciences, Engineering and Medicinehas set a Tolerable Upper Intake Level, or UL. This is the maximum daily intake unlikely to cause adverse health effects for vitamins and minerals; dosages above this can be harmful.
The side effects you could experience will depend on the supplement you are taking, the dosage, duration and whether you take other vitamins, minerals or medicines or have any health conditions. Side effects range from mild symptoms like headaches, to—in the most severe instances—death.
Vitamin A
Vitamin A is a fat-soluble vitamin that plays a role in healthy vision, immune system function, reproduction and growth. Optimal intake is also important in maintaining liver and heart health. Certain animal-based foods, like fish, organ meats, dairy products and eggs, contain the active form of vitamin A, also known as retinol (preformed vitamin A). Plant-based foods have beta carotene, or pro vitamin A, which can be converted to vitamin A in the body.
TheRecommended Dietary Allowance (RDA) for vitamin Ais listed in retinol activity equivalents (RAE) and varies based on age and gender. For adult men, the RDA is 900 micrograms RAE a day, and it’s 700 mcg for adult females. One egg, for example, provides 75 mcg RAE of vitamin A.
Certain populations may need to supplement with vitamin A, such as those with gastrointestinal disorders, cystic fibrosis andiron-deficiency anemia. The UL for preformed vitamin A includes intakes from all sources—food, beverages and supplements—and is set at 3,000 mcg for adults 19 and older. There are no established upper limits for beta carotene or other sources of provitamin A.
Too much preformed vitamin A can cause headache, blurred vision, nausea, dizziness, muscle aches and problems with coordination. In severe cases it can lead to coma and death. When used during pregnancy, too much vitamin A may cause birth defects.
According to theNational Institutes of Health Office of Dietary Supplements, high intakes of beta carotene do not tend to cause the same problems. (Although too much might make your skin turn yellow, which will resolve once consumption drops down.) However, people who smoke should be cautious, as high doses of beta carotene have been associated with an increased risk for lung cancer and death.
Vitamin D
Vitamin D is an important fat-soluble vitamin involved in building and maintaining healthy bones and teeth, immune system function, reducing inflammation and helping with glucose metabolism, to name a few. Vitamin D deficiency has been linked to heart disease, diabetes, certain cancers, autoimmune diseases and neurological disorders, according to an article published inAging and Disease.
Vitamin D is found in a limited number of foods, and is largely made in the body when your skin is exposed to sunlight—that’s why it’s called the “sunshine vitamin.” Foods that contain vitamin D include fortified foods, like cereal, dairy products and plant-based milks, wild-caught fish such as salmon, pasture-raised eggs, beef liver, cod liver oil, and mushrooms grown under UV light.
The RDA for vitamin D is 600 IU—or 15 mcg—for people ages 14 to 70. And there are various reasons why it’s commonly taken as a supplement. Vitamin D may help prevent osteoporosis, promote immunity and prevent muscle loss among those who have suboptimal dietary intake and during cold months when sun exposure is limited.
If you have a vitamin D deficiency (your doctor can do a simple blood test to tell whether you do), supplementation may be required. The amount you need will vary depending on how low your blood levels are. Sometimes, supplement doses are recommended above the UL of 4,000 IU—or 100 mcg—for short periods of time to correct a deficiency.
But because vitamin D is fat-soluble, excess consumption for long periods of time can cause vitamin toxicity. While rare, it can happen, and usually occurs from supplemental use. TheODSreports that extremely high levels of vitamin D in the blood (150 ng/ml or 375 nmol/l) can cause:
Vitamin E
This is a powerful antioxidant that is important for immune, cellular and vascular health. It can be consumed through vegetable oils, wheat germ, nuts, seeds, green leafy vegetables and fortified foods (think breakfast cereals and margarine).
The RDA for vitamin E is 15 milligrams per day, while theUL for natural or synthetic supplements is 1,000 mg daily(1,500 IU a day for natural vitamin E supplements and 1,100 for synthetic). The natural form of vitamin E is called alpha-tocopherol and the synthetic form is DI-alpha-tocopherol. Some supplements are sold as mixed tocopherols.
Vitamin K
Vitamin K is a fat-soluble vitamin involved in blood clotting andis an important component to bone health. It’s found in green leafy vegetables and can be taken in supplemental form. Most people do not need a vitamin K supplement because it is found abundantly in the diet and deficiencies are rare. However, certain populations are at greater risk for low levels of K, including those who have had bariatric surgery, and people withcystic fibrosis, celiac disease, ulcerative colitis and short bowel syndrome.
The Daily Reference Intake (DRI) for vitamin K is established as an Adequate Intake (intake at this level is assumed to ensure nutritional adequacy, and is used when evidence is insufficient to develop an RDA). It’s set as 120 mcg per day for men 19 and older and 90 mcg for women.
There’s no set UL for vitamin K, because there is limited evidence of toxicity. However, people who take certain medications, like blood thinners, should not supplement with vitamin K. And in some cases, too much could trigger allergic reactions and the potential for liver damage.
Vitamin B6
Vitamin B6 is a water-soluble vitamin involved in many enzymatic functions, including protein synthesis, immune function and cognitive function, to name a few. It is found in a variety of foods like fish, beef, organ meats, fortified foods, starchy vegetables and fruit.
The RDA for vitamin B6 is 1.3 mg daily for adults ages 19 to 50. The UL of 100 mg a day is much lower than dosages associated with adverse effects.
Sensory neuropathy (numbness and tingling in the hands and feet) is associated with 1 to 6 grams of vitamin B6 when taken for 12 to 40 months,although it usually goes away once the supplement is discontinued. Other potential effects of long-term excessive intake include increasing your sensitivity to the sun, as well as nausea and heartburn.
Iron
The RDA for iron is 8 mg for males ages 19 to 50 and 18 mg for adult women. Iron needs increase during pregnancy and lactation. People who have iron deficiency, iron-deficiency anemia, those who follow a strict vegan or vegetarian diet, pregnant and nursing women, and those who have heavy periods may benefit from an iron supplement.
The ODSnotes that supplemental iron (25 mg) can reduce zinc absorption. This dosage is commonly found in supplements and may be suggested to treat a deficiency. But this should be under the supervision of a professional. And high-dose supplementation can increase the risk of constipation, nausea, abdominal pain, diarrhea and vomiting. While these symptoms are not toxic, they are certainly unpleasant. According to theODS, short-term intake of doses much higher (20 mg/kg) can also lead to necrosis of the intestine, especially when not taken with food.
Zinc
Zinc is required to activate certain immune cells and acts as a powerful antioxidant. It is also important in wound healing. Zinc deficiency is associated with impaired immune function and increased risk of infections in certain groups.
Foods rich in zinc include seafood, grass-fed beef, organic chicken (dark meat), raw pumpkin seeds, cashews and chickpeas. The RDA for zinc is 8 mg a day for women 19 and up and 11 mg a day for men. The UL is 40 mg a day for males and females ages 19 to 50.
Takingmore than 100 mg per day can lead to adverse effects, like an increased risk of prostate cancer, fever, chills and/or headaches. Long-term zinc supplementation can result in a copper deficiency.
Vitamins and minerals, when taken above the Tolerable Upper Intake for extended periods of time can be harmful and sometimes toxic. However, there are times when supplementation is necessary. Regulated supplementation can be used to meet nutrient requirements or to treat a deficiency. TheAcademy of Nutrition and Dieteticshighlights times when supplementation might be necessary:
Certain groups are also more vulnerable to micronutrient inadequacy due to age, increased needs or absorption problems. These groups include older adults, pregnant and lactating women, alcohol-dependent individuals, those who follow strict vegetarian or vegan diets, and those with increased nutrient needs due to medications or disease.
If you fit into one of these groups, you may need supplementation. The best way to take supplements safely is to consult with a registered dietitian (RD), who can assess your nutrient intake and establish safe levels of supplemental dosages.
If you are unable to meet with an RD, consider talking with your health care provider, and stick to doses with no more than 100% of the RDA. Look for supplements with independent verification, which ensures that the supplement you are purchasing contains what it says it does and is not contaminated with other ingredients. Independent verification companies like NSF, USP and ConsumerLab are independent organizations that review the manufacturing process of products. This can include product testing and facility audits.
The Bottom Line
Supplements can be used to fill the gaps to meet nutrient needs or to correct micronutrient deficiencies. Certain populations are at a greater risk of developing insufficiencies and deficiencies. However, high-dose supplements without medical supervision, especially fat-soluble vitamins, can be toxic. Before starting any type of supplement, you should discuss it with a medical professional, preferably a registered dietitian.
Frequently Asked Questions
Unlike water-soluble vitamins which get excreted via urine when taken in excess doses, fat-soluble vitamins are stored in the body. Excess intake can lead to an overload of vitamins such as A, D and E.
Water-soluble vitamins have the lowest risk for toxicity; however, when taken in excess amounts much higher than the Tolerable Upper Intake they can cause unpleasant symptoms. For example, high doses of vitamin B6 can cause numbness and tingling in the hands and feet, which usually stops once you stop taking the supplement.
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