And some of these supplements are sold the form of extra strong “mega-doses”—tens or hundreds of times higher than recommended daily amounts—which can increase the chances of taking too much.
“Mega-dose vitamins or dietary supplements may be harmful to consumers,” Rui Hai Liu, a professor in the Department of Food Science at Cornell University, told Newsweek.
People with deficiencies of certain vitamins or minerals may benefit from taking relatively high doses of a given supplement for a limited period of time, although it is important to consult with a health care provider before implementing any supplementation protocols.
But in general, Liu said: “Do not take mega-dose vitamins or dietary supplements.”
Supplements are not intended to replace a healthy and varied diet. And experts such as Liu recommend that people get their vitamins and antioxidants from foods, not from dietary supplements, to the extent that this is possible.
Can you take too many vitamins?
Consuming large doses of certain single-nutrient supplements or multi-vitamins may have potentially adverse health effects, depending on what is being taken. Compounds that may be particularly problematic when taken in very high doses, include vitamins A, D, C and B6.
“There are always possibilities of acute and long-term adverse effects when supplementing any substance, including vitamins,” Seattle-based registered dietitian nutritionist, Ginger Hultin—owner of Ginger Hultin Nutrition and author of the Meal Prep for Weight Loss 101 e-book—told Newsweek.
“It’s important to know that taking a dietary supplement is generally safe when taken in the right doses, for the right reasons. It’s definitely worth working with a professional like a registered dietitian or primary care physician who can help you navigate the complexity,” she said.
There are two main groups of vitamins: fat-soluble and water-soluble. The body absorbs the former—which do not dissolve in water—like it does dietary fats, storing them for long periods. The fat-soluble vitamins are A, D, E and K.
The latter group, on the other hand, dissolve in water and are readily absorbed into the tissues of the body. The water-soluble vitamins are vitamin C, plus the B vitamins—B1, B2, B3, B5, B6, B7, B9 and B12.
The body only uses the vitamins and minerals that it needs so excess amounts will be excreted or, perhaps, pose a risk for toxicity. Because fat-soluble vitamins are stored in the body, their toxic potential is higher because excess intakes can build up more easily over time.
In general, taking high doses of water-soluble vitamins is less likely to cause health issues than with fat-soluble vitamins because they are not stored. But sometimes taking megadoses of some water soluble vitamins can also be problematic.
“Fat-soluble vitamins can definitely become toxic at high levels but so can water-soluble vitamins,” Hultin said. “A lot of people say, ‘It’s just expensive pee’—indicating that high doses of water-soluble vitamins aren’t having real effects in the body—but that’s not true.”
For example, very high doses of the water-soluble vitamin C—an antioxidant that plays a role in immune function—can lead to a variety of problems such as diarrhea, nausea, abdominal cramps, and other gastrointestinal issues. The recommended daily intake (RDI) for vitamin C is 90 milligrams for men and 75 milligrams for women, according to the National Institutes of Health.
Meanwhile, taking high doses of vitamin B6 over long periods of time can cause serious health issues, including neurological problems, skin lesions and nausea. The recommended B6 RDI for men and women is 1.3 milligrams. Research indicates that problems can occur when individuals consume anywhere from 1 to 6 grams per day.
When it comes to the fat-soluble vitamins, regularly consuming high quantities of vitamin A can lead to a very rare condition known as hypervitaminosis A, the symptoms of which include nausea, vomiting, increased pressure on the brain, abdominal pain, drowsiness and irritability. In extreme cases, hypervitaminosis A can even result in coma or death.
“Vitamin A is important for eye health and infant development, but excessive intake during pregnancy can cause birth defects,” Hultin said.
Vitamin D toxicity, known as hypervitaminosis D, is also very rare but potentially dangerous. It is characterized by a build up of calcium in the blood that can result in nausea, vomiting, weakness, weight loss, irregular heartbeats, bone pain, organ damage—and in extreme cases, stupor and coma.
“Like any substance, too much of one thing has the potential to cause problems. The same goes with vitamins and minerals,” Hultin said. “I point my clients to the doses set for their age, sex, and life stage by not exceeding the recommended daily allowances.
“In general, vitamins can be beneficial for overall health and wellness. Be smart about which brands you choose and don’t take more than the recommended amount on the label. If you ever have questions about vitamins, talk with your health care provider or registered dietitian nutritionist.”
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