Any ingredient in a multivitamin supplement can be toxic in large quantities, but the most serious risk comes from iron or calcium. High or toxic doses of calcium, vitamin D, and vitamin A can cause nausea, diarrhea, and stomach cramps. Excess selenium can lead to hair loss, gastrointestinal disorders, fatigue, and mild nerve damage. Just because supplements are safe in moderation doesn't mean that more is better.
Combining several supplements or taking doses higher than recommended may increase the risk that they could cause harm. Once the human body uses the vitamins and minerals it needs, the rest is excreted or stored. Manufacturers can add vitamins, minerals and other supplement ingredients to the foods you eat, especially breakfast cereals and beverages. As a result, you may be consuming more of these ingredients than you think, and more may not be better.
Taking more than you need costs more and may also increase the risk of side effects. For example, too much vitamin A can cause headaches and liver damage, reduce bone strength, and cause birth defects. Too much iron causes nausea and vomiting and can damage the liver and other organs. David Jenkins also said that, when taken in moderation, most vitamin and mineral supplements cause no harm.
Popular supplements include vitamins D and B12; minerals such as calcium and iron; herbs such as echinacea and garlic; and products such as glucosamine, probiotics, and fish oils. You're more likely to have side effects from dietary supplements if you take them in high doses or instead of prescription drugs, or if you take many different supplements. In addition to vitamins, dietary supplements may contain minerals, herbs or other botanical ingredients, amino acids, enzymes, and many other ingredients. Also, be careful when giving supplements to a child unless recommended by their health care provider. The federal government can take legal action against companies and websites that sell dietary supplements when companies make false or misleading statements about their products, if they promote them as treatments or cures for diseases, or if their products are not safe.
Even if none of the supplements separately exceeds the maximum limit for a given nutrient, combining several pills can result in doses higher than recommended. Some dietary supplements can help you get adequate amounts of essential nutrients if you don't eat a variety of nutritious foods. If you think you've had an adverse reaction to a dietary supplement, tell your healthcare provider. However, some studies show no evidence that many popular supplements have real health benefits, leading many scientists to change some of their recommendations. The only way to know for sure if a supplement contains the amounts of vitamins listed on the label is if it has been tested by an independent third party such as ConsumerLab. The FDA has established good manufacturing practices (GMP) that companies must follow to help ensure the identity, purity, concentration and composition of their dietary supplements.
Some supplements may increase the risk of bleeding or if taken before surgery may change the response to anesthesia. Johanna Dwyer DSC RD senior nutrition scientist in the Office of Dietary Supplements at the National Institutes of Health professor of medicine (nutrition) and community health at the Tufts University School of Medicine also noted that some supplements can interfere with laboratory tests especially high doses of biotin (often found in hair and nail supplements).It is important to remember that just because supplements are safe in moderation doesn't mean that more is better. Be careful when giving supplements to a child unless recommended by their health care provider as well as when taking multiple dietary supplements at once.
