Dangerous Side Effects and Risks of 8 Popular Supplements

More than 50% of adults in the United States use dietary supplements. However, supplements aren’t regulated like medications, so it is essential to be aware of possible dangerous side effects to stay safe and healthy.

Jump to Key Takeaways.

1. Multivitamins: Don’t Replace a Balanced Diet

Multivitamins are the most popular supplement for every age group, but little evidence supports their use. Most experts agree that food is the best way to get your vitamins.

Some serious side effects of the vitamins found in multivitamins include:

• Beta carotene may increase lung cancer risk for people already at high risk (people who smoke and work around asbestos).
• Vitamin K in multivitamins may reduce the effectiveness of Warfarin, a blood-thinning medication.
• Iron and copper in multivitamins can contribute to iron or copper overload, and increase the risk of dementia, diabetes, and cardiovascular disease.
• Calcium and zinc can reduce the effectiveness of antibiotics.

2. Vitamin D: Toxic Calcium Levels

Vitamin D helps the body absorb calcium. Taking excessive amounts of vitamin D for months or more can lead to hypercalcemia (toxic calcium levels), leading to symptoms such as:

• Nausea
• Vomiting
• Muscle weakness
• Pain
• Loss of appetite
• Dehydration
• Kidney stones
• Neuropsychiatric disturbances

On the most extreme end of the spectrum, vitamin D toxicity can cause:

• Cardiac arrhythmias
• Kidney failure
• Calcification of soft tissues (such as heart valves and vessels)
• Death

Getting vitamin D naturally from sunlight or food, rather than supplements, doesn’t cause this complication.

3. Omega-3s: Immune and Bleeding Complications

Omega-3 fatty acids (often found in fish oil pills) can cause severe side effects when taken in high doses. These include:

• Reduced immune function due to the lowered inflammatory response caused by omega-3 fatty acids.
• Bleeding for extended periods due to reduced platelet aggregation, when blood cells clump together to form a blood clot.
• Increased risk for atrial fibrillation (irregular heart rhythm) among people with cardiovascular disease.

It’s vital to discuss fish oil dosage with your healthcare provider. Experts recommend taking two long-chain omega-3 fatty acids—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—in daily doses of no more than 5 grams (g).

4. Vitamin C: Kidney Stones and Drug Interactions

Vitamin C supplements are generally safe, and toxicity is rare because it’s a water-soluble vitamin (meaning that excess amounts are eliminated in your urine).

However, there is some evidence that high doses of vitamin C can increase the risk of kidney stones, especially for men and people already predisposed to kidney stones.

Vitamin C supplements can also cause dangerous interactions with certain medications. It’s critical to discuss adding vitamin C to your routine if you take any of the following medications:

• Chemotherapy
• Radiation
• Statins

5. Calcium: Hardening of the Arteries

Calcium supplements may increase the risk of atherosclerosis (hardening of the arteries), resulting in symptoms such as:

• Renal insufficiency
• Poor muscle tone
• Constipation
• Nausea
• Weight loss
• Fatigue
• Heart arrhythmias
• Higher risk of death from cardiovascular disease

Taking large amounts of calcium can lead to serious health complications. Although the research is somewhat mixed, scientists believe that taking high amounts of calcium may increase the risk of developing:

• Cardiovascular disease
• Kidney stones
• Prostate cancer

Experts recommend that adults 19–50 take no more than 2,500 mg of calcium per day, and for those 51 and over, the upper limit is reduced to 2,000 mg to avoid side effects.

6. Magnesium: Digestive Upset and Toxicity

Taking high doses of magnesium from supplements can cause uncomfortable gastrointestinal side effects, such as abdominal cramping, gas, and diarrhea.

When taken in doses over 5,000 milligrams (mg) per day, or by those with poor kidney function, magnesium can lead to toxicity, a rare but dangerous occurrence.

Symptoms of magnesium toxicity include:

• Low blood pressure and fainting
• Nausea
• Vomiting
• Flushed face
• Inability to urinate
• Depression
• Lethargy and muscle weakness
• Difficulty breathing
• Irregular heartbeat
• Cardiac arrest (heart attack)

Adults 19 and older should not take more than 350 mg of magnesium per day to avoid side effects and reduce the chance of toxicity.

7. Probiotics: Infection for Immunocompromised Individuals

Probiotics are live microorganisms that can have a positive effect on your health. Sometimes they’re called “good bacteria.”

When taking probiotics, some people can experience side effects, like gas, bloating, and an upset stomach.

However, those who are immunocompromised or severely ill should speak to a healthcare provider before using probiotics, as they can result in severe infections, such as:

• Bacteremia: A bacterial infection in the blood; also called blood poisoning or sepsis
• Fungemia: A fungal infection in the blood.

8. Iron: Dangerous Overdose Risks

Low doses of iron supplements can cause various digestive side effects, and very high doses can be dangerous.

Although rare, it is possible to overdose on iron supplements. Since 1997, the Food and Drug Administration (FDA) has required that any iron supplements sold in doses higher than 30 mg contain strong warning labels and single-pill packaging.

Iron overdose can cause:

• Blood loss
• Coma
• Convulsions
• Death
• Necrosis (tissue death) of the intestines
• Organ failure
• Shock

Key Takeaways

• Dietary supplements are not regulated in the same way as medications, and severe side effects are possible.
• High dosages of certain popular supplements can cause dangerous side effects and even death.
• Try to get your vitamins and minerals through food as much as possible.