Never Buy Multivitamins With These 6 Ingredients, Doctors Say

If you feel your diet is falling short, the best thing to do is to make a diversified, healthy meal plan that fills in the nutritional gaps. That's because though one-third of all American adults currently take supplemental vitamins, research has returned mixed results about their efficacy. In some cases, taking a daily multivitamin with certain ingredients can even cause more harm than good, leading many doctors to advise against their use.

"In general, I wouldn't recommend taking over-the-counter (OTC) multivitamin supplements that do not target specific deficiencies or achieve particular objectives," says Thomas Pontinen, MD, a double-board certified physician and co-founder of MAPS Center for Pain Control. "The best approach to supplementation is to consult with a doctor to develop a customized regime based on your specific needs."

However, if you do plan to keep taking multivitamins, the next best thing is to review the ingredient list and ensure that you're not going overboard on any one thing. Wondering what to look for on the label? These are the top six ingredients to take notes of, doctors say.

RELATED: 12 Supplements You Should Never Take Together, Medical Experts Say.

Amber Robins, MD, a double board-certified family and lifestyle medicine doctor, says you should never buy multivitamins with excessive amounts of calcium.

"For some who have high calcium levels, adding more calcium in their diet may lead to having harmful side effects," Robins tells Best Life. "Kidney stones, constipation, and altered mental status are all symptoms of having elevated calcium levels."

According to medical experts from Mount Sinai, "any ingredient in a multiple vitamin supplement can be toxic in large amounts." However, they note that calcium is one of two ingredients—iron being the other—that comes with "the most serious risks."

For people without an iron deficiency, taking a multivitamin with added iron can cause potentially serious side effects.

"In healthy people, taking high doses of iron supplements (especially on an empty stomach) can cause an upset stomach, constipation, nausea, abdominal pain, vomiting, and diarrhea," says the National Institutes of Health (NIH). "Large amounts of iron might also cause more serious effects, including inflammation of the stomach lining and ulcers. High doses of iron can also decrease zinc absorption."

"Though iron can be important if you have iron deficiency anemia, everyone may not need it in their daily multivitamin if their blood count is normal," adds Robins.

RELATED: 5 Surprising Benefits of Taking Vitamin B-12 Every Day.

Pontinen says that like calcium, other metallic elements such as copper can be problematic when found in multivitamins in high doses.

"There are specific recommended intake amounts for these nutrients, and the human body relies on a careful balance of trace minerals to complete basic health functions," he explains. "Too much copper can make you feel sick and even harm the kidneys, liver, heart, and brain. Both minerals [calcium and copper] are crucial for life function, but I'd recommend avoiding them in supplements unless you know you need them."

Vitamin A serves a wide range of functions in the body. Namely, it can help you maintain healthy organs, a healthy immune system, reproductive system, and eyesight.

However, experts say that you should be able to get all of the vitamin A you need through your diet and that too much vitamin A can cause adverse effects in some.

"Pregnant women are especially advised to be wary of taking supplements with pure vitamin A, as too much intake of the vitamin has been shown to cause some problems in fetal development," Pontinen notes. "You may opt for beta-carotene instead, which is a precursor to vitamin A that the body has to process first."

RELATED: What Happens to Your Body If You Take Vitamins on an Empty Stomach.

Sugar is an inactive ingredient found in some multivitamins. "This can be included in pills and gummies. In order to avoid unnecessary extra sugar intake, it is helpful to try to take multivitamins that do not have sugar in them or have limited amounts," Robins says.

Pontinen recommends against products that contain sugar alcohols, too. "Sugar alcohols, like sorbitol and xylitol, are sometimes added to multivitamins to improve taste or texture. However, they can cause digestive issues like bloating and gas in some people, and some of the new sugar alcohols on the market haven't been researched enough to properly determine long-term safety," he says.

Finally, Pontinen recommends against multivitamins that contain dl-alpha-tocopherol, a synthetic form of vitamin E, commonly found in many multivitamin supplements.ae0fcc31ae342fd3a1346ebb1f342fcb

"While it shares the name vitamin E with other forms, like the natural RRR-alpha-tocopherol, it is absorbed far less efficiently by the body and may cause side effects like nausea and digestive issues," he says.

Best Life offers the most up-to-date information from top experts, new research, and health agencies, but our content is not meant to be a substitute for professional guidance. When it comes to the medication you're taking or any other health questions you have, always consult your healthcare provider directly.