2. Vitamin E
Once thought to reduce the risk of cardiovascular disease, Alzheimer’s, cataracts, and cancer, vitamin E may actually increase some cancer risks. One study found an increased risk of cancer in men taking 400 IU daily (the recommended intake is 22 IU). Another study found the overall risk of death is higher in men and women who supplement with high doses of vitamin E than those who don’t. If you’re worried about your daily multi with vitamin E, Cox says you’re okay: “The amount of vitamin E in most multi-vitamins isn’t enough to cause this effect.”
Although some natural healers recommend supplements, iodine should only be taken under a doctor’s supervision. The mineral is most often associated with the thyroid gland, as it is a key component of the hormones produced there, says Maita. “Too little or too much iodine can cause an underactive thyroid, known as hypothyroidism,” says Maita, so it’s particularly important to make sure you’re not supplementing when you don’t need to. The best way to tell? Ask your doctor to measure your iodine levels in your urine, says Maitra, to determine if your levels are low before you take a supplement. And keep in mind that our food in this country is already supplemented with iodine, says Khara Lucius, ND, a naturopathic oncologist at Cancer Treatment Centers of America, which means iodine deficiency is rare.
This mineral helps form hemoglobin, a component of your blood that delivers oxygen from the lungs throughout the body. Iron is also necessary for normal cellular functioning and the synthesis of some hormones. However, you should only take it as a supplement when you have laboratory confirmation of a deficiency through your doctor, says Lucius. “That’s because iron overload due to excessive supplementation or dietary intake can damage the liver and possibly other organs, such as the pancreas and heart.” Maitra agrees, adding that too much iron can also cause liver inflammation and can oxidize in the body, causing cellular damage.
5. Vitamin B6
The eight B vitamins referred to as “the B complex” are crucial for optimal health, helping our bodies convert our food into fuel and promoting healthy skin, memory, pregnancies, and more. Since the B vitamins are present in many foods—particularly those that are a part of a healthy diet, such as fruits, veggies, whole grains, poultry, and fish—most of us get enough. And research shows that taking B6 supplements over a long period of time can actually cause serious problems. “Even though vitamin B6 is water soluble and safe at the recommended levels, too much can be toxic,” says Maita. “High doses have been shown to cause abnormal sensations in nerves called neuropathy.”