Risk of Popular Supplements, From Vitamin D to Magnesium

• Dietary supplements have become popular among Americans.
• But too much supplements, including fish oil and vitamin D, can be harmful.
• A toxicologist has shared the side effects of excessive consumption of 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 expected to be worth $200 billion by 2025.

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

Additionally, supplements are not approved by the FDA like prescription drugs, so there is a risk that they may be contaminated or cut with other substances not listed on the packaging. A 2023 study, for example, found that 89% of 57 the food supplements tested did not precisely list the ingredients they contained on their labels.

In general, experts agree that it’s best to get nutrients from food, but supplements can be helpful for people with certain deficiencies or poor diets.

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 blood sugar regulation. The recommended daily intake for adults is between 310 and 420 milligrams depending on age and gender, the equivalent of eating a large handful of almonds or eight small potatoes.

Magnesium overdose, which according to the Dietary Supplement Office has been observed in those who took more than 5,000 mg per day, can cause drowsiness, loss of reflexes, facial flushing and, in cases extremes, paralysis and death, according to Chilcott.

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

Chilcott said people with 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 an overdose of vitamin C is extremely rare. Adults should consume 75 to 90 mg per day and can take up to 2,000 mg of vitamin C each day before experiencing negative health effects. — which is about the same amount you would get from eating 28 oranges or 21 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 functioning of the immune system, muscles and nerves, and it is also important for bone strength. People are advised 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 enriched dairy products or vegetable milk.

You’re unlikely to experience symptoms from taking too much vitamin D if you take less than 250 mcg per day, according to the ODS.

Of all the supplements Chilcott discussed, he said this one was potentially the riskiest, 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 blood calcium levels, which can lead to 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 has already reported on a man who died from vitamin D poisoning.

Fish oils

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

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

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

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