Why they may do more harm than good

By | November 20, 2023

There are many important nutritional supplements that benefit people with certain deficiencies or certain health conditions. But research shows, and experts say, some synthetic vitamins could do more harm than good.

“Everyone is always looking for the magic pill that will give them good health, but supplements just aren’t the right fit because the benefits often don’t outweigh the risks,” says JoAnn Manson, chief of preventative medicine at Brigham and Women’s Hospital in Boston, Massachusetts.

This is not to say that some groups of people do not need supplementation with certain nutrients at certain times in their lives; Except most people don’t need to supplement with all the vitamins they think they need.

“In general, I don’t recommend using vitamin supplements unless there is a specific reason for it,” says Walter Willett, a professor of epidemiology and nutrition at the Harvard TH Chan School of Public Health.

This advice applies especially to fat-soluble vitamins.

Water soluble vs. fat soluble

Water-soluble and fat-soluble nutrients are absorbed differently by the body.

Water-soluble vitamins, which include vitamin C and all eight B vitamins, are quickly dissolved, processed and metabolized in the body and are not stored for later use.

“Excess amounts of water-soluble vitamins are excreted in urine,” explains Alice Lichtenstein, head of the cardiovascular nutrition team at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

On the other hand, fat-soluble nutrients—vitamins A, D, E, and K—are stored in the liver and fatty tissue throughout the body for future use. While this helps build up a supply of vitamin D during the summer sun to compensate for reduced sun exposure in the winter months, it also means that these vitamins can build up in potentially toxic levels.

For this reason, the National Academies of Sciences, Engineering, and Medicine provides safety guidelines for the Tolerable Upper Intake Value (UL) to indicate the maximum amount of certain vitamins that can be safely consumed without adverse health effects.

“Fat-soluble vitamins tend to have lower ULs compared to water-soluble vitamins, highlighting the need for caution when consuming,” explains Jen Messer, registered dietitian and president-elect of the New Hampshire Academy of Nutrition and Dietetics.

Among the four fat-soluble vitamins, experts say vitamins A and E are more cautious than others.

Concerns About Vitamin A

Vitamin A is important for vision, growth, reproduction and immune system health. When consumed at the recommended dosage – 900 micrograms daily for adult men and 700 micrograms daily for adult women – from natural food sources such as beef liver, sweet potatoes, spinach, carrots or pumpkin pie, vitamin A is considered safe and essential.

The maximum daily upper limit for vitamin A intake is 3,000 micrograms. However, it is important to note that these amounts include consumption or intake of vitamin A all Sources of vitamin A, including foods, supplements, and creams/lotions that contain retinol. (For context, consider that a single 3-ounce serving of seared beef liver contains 6,582 micrograms of the vitamin.)

Exceeding the UL is dangerous and “a single large dose of it can contribute to toxicity,” explains Yufang Lin, a family physician at the Cleveland Clinic’s Center for Integrative Medicine. Such toxicity can lead to problems such as joint pain, liver damage and birth defects.

“Vitamin A is essential for normal fetal development, but too much of it can harm both the mother and the developing fetus and cause an increased risk of birth defects of the eyes, heart, organs and central nervous system,” says Messer .

Even in small amounts and outside of pregnancy, “vitamin A supplements have been linked to skin irritation and an increased risk of bone fractures,” says Manson.

Research published earlier this year shows that vitamin A toxicity can also be caused by topical vitamin A (retinol), which is used to treat acne and psoriasis.

There have even been problems with the inclusion of vitamin A in multivitamins. “At one point, there were concerns about the amount of vitamin A in multivitamins and bone loss in older women,” explains Lichtenstein. She says that’s why some multivitamin brands now only contain vitamin A as an ingredient in the form of beta-carotene. (Studies show that beta-carotene is converted into vitamin A in the body, but carries fewer of the risks associated with other forms.)

Additionally, some studies show that vitamin A from a balanced diet could reduce the risk of certain cancers; The NIH Office of Dietary Supplements suggests that its supplement form may do this increase the risk of certain cancers due to vitamin A’s role in regulating cell growth and differentiation.

“Long-term, high-dose vitamin A use can also lead to liver disease, elevated blood lipids, bone and muscle pain, and vision problems,” says Kate Zeratsky, registered dietitian at the Mayo Clinic in Rochester, MN. “Early signs of vitamin A toxicity may include dry skin, nausea, headaches, fatigue, large liver, and hair loss, among others.”

Concerns About Vitamin E

Vitamin E is an even more controversial fat-soluble dietary supplement.

When naturally found in foods such as wheat germ oil, avocado, fish, seeds and nuts such as almonds, hazelnuts and peanuts, vitamin E is a powerful antioxidant that protects cells from the effects of free radicals and improves skin and eye health.

However, the Department of Nutrition at Harvard T.H. Chan School of Public Health notes that the safety profile of its synthetic form is controversial among scientists: “Due to occasional reports of negative health effects of vitamin E supplements, scientists have debated whether these Dietary supplements may be harmful and may even increase the risk of death.”

One of the controversial and confusing points about vitamin E is the fact that the nutrient has multiple forms – some of which are better studied than others.

“Vitamin E occurs naturally in eight chemical forms, whereas most vitamin E supplements are synthetic alpha-tocopherol,” explains Lin. It is this alpha-tocopherol form that appears to pose more risks than other forms of vitamin E. “This is an argument that it is better to consume foods rich in vitamin E than a synthetic supplement to take.”

Zeratsky agrees. “I believe there is a need to better understand how the different forms of vitamin E work and interact in our bodies,” she says.

There is also some confusion about how much vitamin E is safe to consume. The recommended daily allowance (RDA) of vitamin E for both adult men and women is 15 milligrams, but the daily upper limit for intake is 1,000 milligrams. The NIH Office of Dietary Supplements notes that “taking vitamin E supplements, even within these upper limits, could be harmful.”

In fact, clinical research shows that taking just 268 milligrams of vitamin E daily can increase the risk of prostate cancer in men by 17 percent. The form used in supplements has also been linked to lung cancer.

“And you don’t have to reach toxic levels to experience disadvantage,” Manson adds. “The randomized trials of vitamin E have documented problems even in moderate amounts.”

Higher doses of vitamin E supplementation can also impair blood clotting, which can lead to bleeding, says Jessika Rose, a bariatric nutritionist at the University of Maryland Upper Chesapeake Health.

Because of these and other issues, a study published by the American Heart Association shows that additional vitamin E supplementation is no longer recommended at the higher levels needed to protect against chronic diseases such as cancer, arthritis and cataracts.

“Ultimately it’s about weighing up the balance between potential risks and opportunities,” explains Messer.

Lack of regulation for dietary supplements

Another area of ​​concern among experts that impacts both water- and fat-soluble vitamins is that supplemental nutrients are not regulated by the U.S. Food and Drug Administration (FDA) under the same criteria as foods and medication.

This can lead to unsubstantiated claims and even labels that misrepresent the ingredients in each supplement bottle. “According to a recent independent analysis of 57 dietary supplements, 84 percent of them did not contain the claimed amount of ingredients, while 40 percent of the dietary supplements did not contain any of the claimed ingredients,” says Messer. “In addition, 12 percent of supplements contained undeclared ingredients, which is prohibited by the FDA.”

So it’s up to consumers to choose reputable supplement brands and buy products that have been tested and labeled by established third parties. “And be very wary of any supplement that claims it can treat a disease, as supplements are not allowed to make such claims,” says Lin.

It is also important to check daily dosage recommendations and upper limits of supplements and to ensure that a supplement you are taking will not interfere with another supplement. “Talk to your doctor or nutritionist to find out what specific nutrients you need,” suggests Rose.

“It is a common misconception that vitamin supplements are beneficial for everyone,” says Messer. “They may be beneficial for certain people in certain situations, but are not necessary everywhere, can be expensive and are not completely risk-free.”

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