Supplement Overload: Can You Overdose on Vitamins?

We often hear about the dangers of vitamin and mineral deficiencies, but what about taking too many?

74 percent of American adults take supplements, but can you get too much of a good thing? RobsPhoto/Shutterstock

Our hectic lifestyles can make it hard to eat well. Some people turn to vitamins, minerals, and other supplements to help pick up the slack. Supplements are supposed to give us more of what we need—but can you get too much of a good thing?

A 2023 poll found that 74 percent of American adults take dietary supplements with 55 percent taking them regularly.

Although their prevalence may make them seem benign, some vitamins and minerals can be harmful if we overdo them, with excess levels leading to toxicity.

Let’s look at four common vitamins and minerals, why we need them, and signs that you may be getting too much.

Vitamins and Minerals

Vitamins can be either water-soluble or fat-soluble. Water-soluble vitamins include C and B vitamins (niacin, folate, thiamine, riboflavin, biotin, pantothenic acid, B6, and B12). Water-soluble vitamins are not stored in the body and are excreted via urine.

Fat-soluble vitamins, however, are stored in the body’s tissues, which means we can take too much, and in excess amounts, they can lead to toxicity. The four fat-soluble vitamins are A, D, E, and K.

Calcium and iron are essential minerals to maintain health, but too much of either can lead to serious side effects as well.

Renee Kindler is a functional medicine and nurse practitioner at Aonani Functional Medicine. When it comes to vitamins, minerals, and hormones, she told The Epoch Times it’s best to follow “the Goldilocks principle.”

“You don’t want too much or too little. Some vitamins and minerals, your body is good at eliminating extra if you have extra, and for some of them, it’s more of a challenge,” she said.

Vitamin A

Vitamin A, also known as retinol, is a fat-soluble vitamin needed for clear vision, a healthy immune system, and growth, development, and reproduction.

Vitamin A can come from animal and plant sources. Preformed vitamin A comes from animal foods like fish, dairy products, eggs, and organ meats. Provitamin A comes from pigments in vegetables and fruit that give them yellow, orange, and red color, called carotenoids—some of which the body can convert into vitamin A. Beta-carotene is the most common vitamin A carotenoid found in foods and dietary supplements, according to the National Institutes of Health (NIH).

The recommended daily allowance, or RDA, of vitamin A we need depends on our age and gender and is measured in micrograms (mcg) of retinol activity equivalents, or RAE.

Note: Recommended daily allowances are often based on the minimum amounts needed to avoid deficiency and disease and not necessarily levels required for optimal health.

According to NIH guidelines, the RDAs for various groups are:

• Adult men (19 years and up)—900 mcg
• Adult women (19 years and up)—700 mcg
• Pregnant women—770 mcg
• Breastfeeding women—1,300 mcg

Too Much Vitamin A

It is possible to get too much (preformed) vitamin A, which is usually a result of taking supplements and medications. Symptoms of high preformed vitamin A include:

• Dizziness
• Nausea
• Blurred vision
• Severe headaches
• Muscle aches
• Coordination problems

In rare extreme cases, excess levels of vitamin A can cause coma and death, and there is a danger of taking too much in pregnancy.

“Vitamin A can cause birth defects, and you can’t reverse that. If somebody’s taking it for acne, a lot of times that can be a childbearing age woman. So that’s something to pay attention to,” Mrs. Kindler says.

Excessive beta-carotene intake can make the skin turn orange, However, this is harmless and can be remedied by taking less.

The NIH states that the upper limit (UL) for vitamin A from all sources is 3000 mcg for adults over 19 years. There are no upper limits for beta-carotene and other forms of provitamin A.

In a study published in the American Journal of Clinical Nutrition in 2019, liver samples from cadavers were examined to determine levels of vitamin A. Liver biopsy is considered the gold standard for assessing vitamin A toxicity but is too expensive and invasive to be used on living subjects. The findings showed that 33 percent (nine of the 27 liver samples) had excess (hypervitaminotic) vitamin A levels, and only 22 percent (six out of 27) found a vitamin A deficiency. The findings suggest that vitamin A toxicity is more prevalent than vitamin A deficiency.

The authors cautioned that because preformed vitamin A is being added to many processed foods, there was an urgent need to develop population biomarkers to diagnose hypervitaminosis before toxicity.

Vitamin A can interact with certain medications. Conversely, some medications can affect the absorption of vitamin A, so speak to your prescribing physician if you are on medications and considering taking a vitamin A supplement.

Vitamin D

Vitamin D, or calciferol, is an essential nutrient we get from the foods we eat and a hormone our bodies produce. The two types of vitamin D vital to human health are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

Vitamin D2 primarily comes from plants, while our vitamin D3 comes from animal sources (about 10 percent), with the rest produced by our bodies from exposure to sunlight. Vitamin D3 is better absorbed and more potent than vitamin D2. The liver and kidneys must convert all the vitamin D2 and D3 we get from foods or supplements into the active form our bodies can use.

Vitamin D is fat-soluble and necessary for our bodies’ absorption of calcium and phosphorus, which are needed to make bones. Without calcium and vitamin D, we are more susceptible to osteoporosis, where bones become weak and are more likely to break.

Vitamin D is essential for our bones, brains, and immune system. It also keeps inflammation in check and allows nerves to carry messages between the brain and the rest of the body.

Vitamin D and the Sun

Our bodies make vitamin D when our skin is exposed to sunlight. However, some things, like clouds, air pollution, old age, and having dark skin, reduce our ability to get vitamin D from sunlight. The NIH also notes that the skin doesn’t produce vitamin D from sunlight through a window.

The amount of vitamin D you need depends on your age and is measured in micrograms (mcg) and international units (IU). The daily recommended amounts per the NIH are:

• Birth to 12 months—10 mcg (400 IU)
• Children 1 to 13—15 mcg (600 IU)
• Teens 14 to 18—15 mcg
• Adults 19 to 70—15 mcg
• Adults 71 years and older—20 mcg (800 IU)
• Pregnant and breastfeeding women: 15 mcg

Too Much Vitamin D

Too much vitamin D can be harmful, and a blood test is the only way to measure how much vitamin D you are getting. Vitamin D deficiency is more common, with estimates that at least 25 percent of American adults are not getting enough.

Very high levels in the blood (more than 375 nanomoles per liter (nmol/L) or 150 nanograms per milliliter (ng/ml) can cause the following symptoms:

• Loss of appetite
• Dehydration
• Muscle weakness
• Nausea
• Vomiting
• Confusion
• Pain
• Excess urination and thirst
• Kidney stones

Extreme levels can cause kidney failure, irregular heartbeat, and death. You can’t get too much vitamin D from the sun, as your body limits how much it produces. High levels are almost always due to supplements.

The NIH has guidance for the upper limits of vitamin D, but some think the levels are much higher. According to the NIH, the daily upper limit (UL) of vitamin D from all sources is as follows:

• Birth to 6 months—25 mcg (1,000 IU)
• Infants 7 to 12 months—38 mcg (1,500 IU)
• Children 1 to 3 years—63 mcg (2,500 IU)
• Children 4 to 8 years—75 mcg (3,000 IU)
• Children 9 to 18 years—100 mcg (4,000 UI)
• Adults 19 and older—100 mcg (4,000 UI)
• Pregnant and breastfeeding women—100 mcg (4000 IU)

Interactions

Vitamin D can interact with medications, including some types of weight loss drugs, statins, steroids, and thiazide diuretics. If you are taking medications, consult your prescribing physician before supplementing with vitamin D.

Calcium

Calcium is the most abundant mineral in the body, and almost all of it is found in our bones and teeth, giving them their strength and structure. We need calcium for proper muscle and nerve function. Our bodies cannot make calcium, and we lose calcium every day through our hair, nails, skin, sweat, and other excretions. We must get enough from our diet to ensure calcium isn’t being taken from our bones, which, if excessive, can lead to osteoporosis.

Dairy foods, green vegetables, fish, beans, nuts, and fruits are rich in calcium. Some foods are also fortified with calcium to help us achieve optimal levels.

Exercise, vitamins D and K, magnesium, and phosphorus help the body absorb calcium and increase bone mass. Other factors that affect calcium absorption include age, diseases (like Crohn’s and celiac), and medications.

Many forms of calcium are available in supplement form, and they differ according to their content, how well they are absorbed, and their cost. The two most common are calcium citrate and calcium carbonate.

The RDA of calcium we need depends on age and gender:

• Adults 19 to 50—1000 milligrams (mg)
• Men 51 to 70—1000 mg
• Women 51 to 70—1200 mg
• Adults 71 and over—1200 mg
• Pregnant and breastfeeding women—1000 mg

According to the Harvard T.H. Chan School of Public Health, the UL for calcium is 2,500 mg daily from food and supplements. They also note that those over fifty shouldn’t take more than 2,000 mg of calcium daily from supplements as it can increase the risk of constipation, kidney stones, and prostate cancer.

Too Much Calcium

Too much calcium results in a condition called hypercalcemia—symptoms of which include:

• Fatigue and weakness
• Vomiting and nausea
• Shortness of breath
• Chest pain
• Heart palpitations and irregular heart rate

Mrs. Kindler also notes the potential dangers of excess calcium.

“Calcium is important not to over supplement because calcium can deposit itself into your arteries and joints—and that’s not a good thing. It also can interfere with the absorption of many other nutrients.”

Interactions

Calcium supplements can interact or interfere with certain medications, and some reduce calcium levels in the body. If you are on medication, consult with your prescribing physician before taking calcium supplements to ensure you are doing it safely.

Iron

Iron is a mineral needed for growth and development. Iron is also an essential component required to make blood. Our bodies need it to make hemoglobin, a protein in red blood cells that helps carry oxygen throughout the body. Iron is also necessary to produce myoglobin, a protein that brings oxygen to the muscles. Iron also helps resist fatigue and supports cognitive function.

The body does not make iron, so we need it from our diet. Iron from supplements comes in various forms, but according to the NIH, the most common are:

• Ferrous sulfate
• Ferrous gluconate
• Ferric citrate
• Ferric sulfate

Iron is available in several multivitamins and other supplements or on its own. Iron can be particularly dangerous for children, and iron overdose is a leading cause of death from poisoning in children under six years of age. Always keep iron supplements safely out of children’s reach.

The iron you need depends on your age, gender, and diet. Vegetarians and vegans who eat a plant-based diet need almost two times (1.8 times) the RDA of iron than meat eaters. The iron from meat, called heme iron, is more bioavailable than the nonheme iron from plant foods. Meat, seafood, and poultry also help the absorption of nonheme iron.

Stephanie McBurnett is a registered dietician, nutritionist, and nutrition educator for the Physicians Committee for Responsible Medicine, a non-profit organization of more than 17,000 physicians dedicated to prevention and empowering patients to take control of their health.

She says iron is probably the most risky to overdo and that men and postmenopausal women only need about eight milligrams daily. So those taking a multivitamin, eating foods high in iron, like meat products, beans, and leafy greens—and supplementing with iron—can quickly push the upper limits and have serious side effects.

“It’s really interesting because the symptoms of having too much iron are very much like the symptoms of having too little iron. So, high iron symptoms are weakness, fatigue, risk of infection, darkened skin, abdominal discomfort—which will probably come from constipation, because too much iron can make you constipated. And long term, they’ve seen an increased cancer risk, especially colon cancer, with high intakes of iron.”

Another consideration is eliminating iron when levels get too high. Mrs. McBurnett points out that blood loss is the only way to eliminate excess iron. For menstruating women, this usually isn’t a problem, but for men, it is a little more complicated. She explains that if their levels are high, they may have to give blood over several months to get their levels back down.

Too Much Iron

It is rare to get too much iron from our diet. However, more than 25 mg of iron from supplements can interfere with the body’s absorption of zinc. High doses of iron from supplements can cause gastrointestinal problems and lead to symptoms including abdominal pain, nausea, vomiting, constipation, and diarrhea. Taking iron supplements with food can help mitigate these effects.

The NIH states that excess consumption of iron supplements of more than 20 mg per kilogram of body weight (approximately 1,365 mg of iron for a 150-pound person) can lead to corrosive necrosis of the intestine, which can cause a variety of complications, including bleeding, shock, tissue damage, and organ failure. It notes that these symptoms can occur, especially if the iron is taken alone and not with food.

Extremely high doses of iron can cause convulsions, coma, organ failure, and death, but these levels would be in the hundreds of thousands of milligrams.

The upper limits of iron for various groups are:

• Birth to 13—40 mg
• 14 and older—45 mg
• Pregnant and breastfeeding women—45 mg

Things to Consider

Vitamin and mineral consumption is a complex topic with multiple factors to consider. Although not an exhaustive list, here are some things to think about:

• The Food and Drug Administration (FDA) does not regulate supplements in the United States, so research the quality and efficacy of the products you use.
• Certain health conditions can affect the absorption of vitamins and minerals (e.g., Crohn’s disease, celiac disease, and ulcerative colitis).
• Medications can affect your vitamin and mineral levels.
• How much you exercise can also affect vitamin and mineral levels.
• Keep track of all the supplements you take to ensure you are not taking too much of one or various types.
• The amount of sunlight you are exposed to (where you live on the planet) affects vitamin D levels.
• In many places, the soil is depleted of vital minerals and nutrients, so no matter how well you eat, you may not be getting adequate vitamins and minerals.
• Consider your likes and dislikes when it comes to food. For example, if you don’t like fish, you may need to take an omega-3 supplement.
• You may be taking vitamin and mineral supplements but not absorbing them efficiently for various reasons. Test your levels occasionally to ensure you are getting enough or not getting too much.
• If you are unwell and unable to determine why, consider excess vitamins or minerals as a potential cause if any symptoms match those above.
• Eat a healthy, varied diet regardless of the supplements you take, as food always provides a much broader array of health benefits.

Mrs. McBurnett agrees, saying the FDA tells us we shouldn’t replace the vitamins from supplements with those we get from a regular, balanced diet.

“There’s so much more in foods than in supplements. You’re just getting one isolated nutrient, vitamin or mineral—but by eating foods, you’re getting fiber, you’re getting micronutrients, macronutrients, you’re getting phytonutrients—especially when you’re eating fruits and veggies.”

Final Thoughts

Given the abundance of supplements on the market, it’s easy to feel overwhelmed about what to take and at what dosage. To ensure you’re getting the right amount of vitamins and minerals and not overdoing it—especially when taking medications or with health conditions—consider working with a dietician, nutritionist, or functional medicine practitioner who can provide expert guidance.

As Mrs. McBurnett points out, “When it comes to vitamins and minerals, more is not always better.”