Risk of Popular Supplements, From Vitamin D to Magnesium

• Dietary supplements have become popular among Americans.
• But too many supplements, including fish oil and vitamin D, can be harmful.
• A toxicologist shared the side effects of overdoing it with some of the most popular supplements.

Dietary supplements are big business. Surveys suggest that more than half of American adults take them, and the market is projected to be worth $200 billion by 2025.

But while we may think supplements are safe, even the most popular ones can be dangerous if we take too much or interact with other medications, Professor Rob Chilcott, head of toxicology at the University of Hertfordshire, UK, told Business Insider.

What’s more, supplements are not approved by the FDA like prescription drugs, so there is a risk that they could be contaminated or cut with other substances not mentioned on the package. A 2023 study, for example, found that 89% of 57 The dietary supplements analyzed did not accurately list the ingredients they contained on their labels.

Experts generally agree that it is best to get nutrients from food, but supplements can be helpful for people with certain deficiencies or whose diets are poor.

Chilcott shared the long-term risks of taking too much of some of the most popular supplements.

Magnesium

Magnesium is essential for muscle and nerve function and regulating blood sugar levels. The recommended daily amount for adults is between 310 and 420 milligrams depending on age and sex, or the equivalent of eating a large handful of almonds or eight small potatoes.

Magnesium overdose, which the Office of Dietary Supplements says has been seen in those who have taken more than 5,000 mg in a day, can cause drowsiness, loss of reflexes, facial flushing, and, in extreme cases, paralysis and death, according to Chilcott.

Consuming too much magnesium can also lead to extremely low levels of calcium, called hypocalcemia, which Chilcott says can “cause a host of health problems.” These include depression, seizures and arrhythmia, according to the Cleveland Clinic.

Chilcott said people who have poor kidney function or hypothyroidism are at particular risk of magnesium overdose.

Vitamin C

Vitamin C helps the immune system function and the body absorb iron. Chilcott said it is generally considered safe and that vitamin C overdose is extremely rare. Adults should consume between 75 and 90 mg per day and can take up to 2,000 mg of vitamin C per day before experiencing negative health effects. — which is about the same amount you would get from eating 28 oranges or 21 bell peppers.

Chilcott said taking more than 2,000 mg of magnesium per day can cause fatigue, kidney problems and vitamin B12 deficiencies.

He said people with gout, cirrhosis and certain kidney diseases should especially avoid high doses of vitamin C.

Vitamin D

The body needs vitamin D for the immune system, muscles and nerves to function, and it is also important for strong bones. People are recommended to consume 15 micrograms of vitamin D per day and no more than 100 mcg, according to the ODS, which is about the same amount you would get from 13.5 eggs or five cups of fortified dairy or plant-based milk.

You are unlikely to have symptoms from taking too much vitamin D if you take less than 250 mcg a day, according to the ODS.

Of all the supplements Chilcott talked about, he said this was the one with the greatest potential risk, but only at very high doses. “The known health benefits of taking a recommended dose far outweigh the risks,” he said.

According to Chilcott, Consuming too much vitamin D is dangerous because it increases calcium levels in the blood, which can cause conjunctivitis, pain, fever and chills, vomiting, and weight loss.

The main condition that increases susceptibility to vitamin D toxicity is kidney disease, he said.

BI previously reported on a man who died from vitamin D toxicity.

fish oils

Omega-3 fatty acids found in foods like fish are important for cellular health and have many functions in the heart, blood vessels, lungs, immune system and endocrine system, according to ODS.

The U.S. Food and Drug Administration says it’s safe to take up to 2 grams of fish oil supplements per day, which is equivalent to eating a three-ounce serving of cooked farmed salmon.

Chilcott said the main risk associated with fish oil is the contaminants the fish may have consumed while they were alive, rather than the supplements themselves. These toxins can include heavy metals such as mercury, lead, and cadmium.

The ODS says that methylmercury, a heavy metal, is removed from fish oil supplements during processing and purification, and a 2021 study found that the supplements they tested did not contain arsenic, cadmium, copper, iron, or mercury. However, the same study found that some of the supplements did contain lead.