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11 Vitamins That May Be Dangerous, Warn Experts

Millions of Americans take vitamins on a daily basis, but some don't provide the health benefits consumers might think. When taken incorrectly, vitamins can actually be harmful and there's also the debate on whether we need vitamins at all with some experts saying that a healthy balanced diet is enough. Megan Mescher-Cox, DO Diplomate, American Board of Internal Medicine, Lifestyle Medicine and Obesity Medicine Identity Medical Group/Dignity Health Medical Group, explains, "keep in mind that the supplement industry is a multi-billion dollar industry. Put frankly, the goal of the supplement industry is to sell supplements, not to keep you healthy and please keep in mind that if it sounds too good to be true, it probably is. I stress that supplements should be treated with the same vigilance as pharmaceuticals. Make certain to talk to your physician before introducing it into your body." 

She adds, "In fact, doing the same with foods would also be helpful. Multiple times daily I find myself counseling patients to stop taking supplements. Often they do no good and sometimes they can even be harmful. Moreover, even though we know about the dangers of megadosing some vitamins, we do not know yet about the long term effects of taking daily doses of many of these vitamins. Globally, we have a deficiency of fruits and vegetables in our diets – we do not have a supplement deficiency. For people that want to improve their health, focus on the basics: a diet rich in vegetables, fruits, legumes (beans, lentils, peas), whole grains with nuts and seeds, regular exercise, restorative sleep, minimizing stress and having a healthy social life. As I tell patients often: true health does not come in pill form. Read the tips below to find out the five vitamins Cox says can be damaging—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Vitamin A, D, E and K – the fat soluble vitamins.

vitamin a supplement

It's common for people to take fat soluble vitamins, but Cox explains why they're not always beneficial. "Vitamin A, D, E, and K are the fat soluble vitamins, which means that they are stored in human adipose tissue. Excess levels build up in the adipose tissue and can cause toxicity or non-specific symptoms related to the excess intake of vitamins. Although toxicity is possible, it is rare to see a person with toxicity. More often we see non-specific symptoms such as fatigue, difficulty concentrating or sleeping, or just not feeling right. It is not recommended to take vitamin A, E, or K vitamins unless directed by a physician and for vitamin D, if someone is taking a supplement to keep the Vitamin D3 supplement at or below 2000 IU daily unless directed by a physician."

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Wooden spoon of Calcium carbonate tablets above glass of milk

While it's important to maintain a healthy dose of calcium to keep bones strong, Cox explains why supplements might not be right for you. 

"Calcium supplements used to be widely taken – and recommended by the medical community– for bone health but later research proved that calcium supplementation to more cardiovascular events. Calcium supplementation has been widely used for bone health. Although supplementation has shown a decrease in overall fracture risk, it has not been shown to decrease the risk of hip fractures, which are the fractures that result in the most shortening of life. They come with risks as well. In 2010, a meta-analysis on calcium supplementation concluded that calcium supplementation is associated with an increased risk of myocardial infarction (heart attack). Of note, getting calcium from food was not associated with an increased risk of myocardial infarction. The United States Preventive Services TaskForce (USPSTF) actually recommends AGAINST supplementing calcium and vitamin D in post- menopausal women of average risk for osteoporosis.

There is also debate about the ideal level of calcium intake. The United States recommends getting at least 1200 mg daily whereas the United Kingdom recommends 700 mg and the World Health Organization recommends 500 mg daily. Many of us more educated in nutrition will advise going by the United Kingdom recommendation of at least 700 mg daily and to get it from food sources. Healthful foods that are rich in calcium include unsweetened plant milks, tofu that is made with a calcium binder (you can find this on the packaging), dark leafy greens such as kale, bok choy and collard greens, soy and navy beans."


Vitamin B6

Vitamin B6 pills forming the word 'B6' over turquoise background.

"Although vitamin B6 is a water soluble vitamin, taking too much can still result in dangers," Cox says. "People can experience neurologic symptoms such as numbness and tingling especially of the fingers and toes but sometimes other parts of the body. I have had multiple patients with neurologic symptoms and vitamin B6 levels well above normal and their symptoms go away when we stop supplementation. Sometimes the excess vitamin B6 is coming in even from a multivitamin. It is very unusual to see too much vitamin

B6 from foods so sticking to the food source is best."

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To support immune health, many people turn to zinc, but Cox reveals why that's not always a good idea. "Zinc supplements have been widely used to help prevent infection, especially during the COVID pandemic, but they can be harmful too. High doses of zinc intake can lead to depletion of copper levels. It can also lead to stomach upset, nausea, vomiting, and loss of taste. Zinc has been tied to immunity because it is necessary for optimal immune function but the key is to prevent deficiency. If someone really wants to take zinc, I recommend that they do not take it for more than a week at any one time or if they desire taking it long term, no more than 25 mg twice weekly at most. For immunity, the best thing we can do is to give the body what it needs: adequate rest, a healthful antioxidant rich diet, regular exercise and minimizing emotional stress. Herbs and spices, vegetables and fruits are high in antioxidants and also anti-inflammatory to help counter inflammation in the body."



Red pills of Iron supplements

"Iron supplementation should never be done without clear instruction from a healthcare professional. Iron is a pro-oxidant which means that it causes oxidative stress and DNA damage in the body," Cox warns. "Iron supplementation increases our risk for colon cancer, heart disease, neurodegenerative disorders amongst others. The body does not have a mechanism to get rid of excess iron so it is even more important to avoid excess iron consumption. If someone has known iron deficiency anemia and wants to improve iron intake thru food, chickpeas and pumpkin seeds as good sources and iron overdose from plant-based foods is extremely rare (please note that iron overdose is possible from animal foods as the type of iron found in animal foods is more readily absorbed in the human body). If someone is found to be iron deficient, it is also important that they work with their health care provider to identify the root cause of the deficiency as taking the supplement may mask an underlying problem."

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Is It Harmful For Children To Take Vitamins

A happy kid holding a vitamin.

If you're considering giving your child vitamins, Cox says, "The American Academy of Pediatrics stance is that healthy children receiving a normal, well-balanced diet do not need to supplement with vitamins (although they do note the importance of a vitamin D supplement of 400 IU daily for children under 1 and 600 IU daily for children over 1 year of age). Megadoses of vitamins, including A, C, or D can produce toxic symptoms in children. For children, iron can be especially dangerous unless specifically recommended by a healthcare provider. Iron toxicity can happen as the supplements can look like candy and be ingested in large amounts. This is the reason why many prenatal vitamins, which usually contain iron, do not contain iron when they come in the gummy form."

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Pregnancy and Vitamins

pregnancy supplements

It's always important to stay healthy and active, especially during pregnancy, but Cox explains the risks to avoid during pregnancy. "When pregnant, please do not take any vitamins or supplements without talking with your doctor first. Vitamin deficiencies and vitamin overdoses can affect the fetus more than adults and it is critical to discuss with your physician. The exception to this would be a prenatal vitamin which should be initiated as early as possible, ideally when one is trying to become pregnant."

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Can I Take Vitamins With A Chronic Disease

physician medicine doctor or pharmacist sitting at worktable, holding jar of pills in hands and writing prescription on special form.

If you have a chronic disease and want to take vitamins, Cox says, "Living with a chronic disease is unfortunately very common and with the disease, certain functions in the body are compromised. For instance, the liver and kidneys work to metabolize and eliminate most pharmaceuticals and supplements. If there is damage to one of these organs, or other organs, the expected blood concentrations of that pharmaceutical or supplement may be higher than expected. Sometimes patients are not aware of the degree of damage to their organs and it is critical to talk to a doctor before starting a supplement. Just as someone should not take a new pharmaceutical without their health care provider knowing, they should not start a supplement without talking to their doctor either."

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