Companies are increasingly adding vitamins and minerals to juices, sports drinks and bottled water, responding to a growing consumer demand for these products. Even though the amounts of added nutrients in these drinks are typically small, some nutrition scientists are concerned that through their overall diets, many people may be ingesting levels of vitamins and other nutrients that are not only unnecessary, but potentially harmful.
“You have vitamins and minerals that occur naturally in foods, and then you have people taking supplements, and then you have all these fortified foods,” said Mridul Datta, an assistant professor in the department of nutrition science at Purdue University. “It adds up to quite an excess. There’s the potential for people to get a lot more of these vitamins than they need.”
Today more than ever, studies show, the average person is exposed to unusually high levels of vitamins and minerals. Already, more than half of all adults in the United States take a multivitamin or dietary supplement. Bread, milk and other foods are often fortified with folic acid, niacin and vitamins A and D.
A study published in July found that many people are exceeding the safe limits of nutrient intakes established by the Institute of Medicine. And research shows that people who take dietary supplements are often the ones who need them the least.
Particularly concerning, experts say, is the explosion of beverages marketed specifically for their high levels of antioxidants, like Vitaminwater, POM Wonderful, Naked Juice and many others. The body requires antioxidants to neutralize free radicals that can damage cells and their DNA. But it also uses free radicals to fight off infections and cancer cells, experts say, and when antioxidants are present in excess, it can throw things out of balance.
A study published this month analyzed 46 beverages — both with and without sugar — sold in supermarkets alongside bottled water. It found that many of these drinks contained vitamins B6, B12, niacin and vitamin C in quantities “well in excess” of the average daily requirements for young adults.
Eighteen of these drinks contained more than triple the daily requirement for B6. Eleven had more than three times the requirement for B12. And a half dozen had more than three times the requirement for niacin or riboflavin. Some of these products promised improvements in energy and immune function, while others promoted “performance and emotional benefits related to nutrient formulations that go beyond conventional nutritional science,” the researchers said.
The most common nutrients added were vitamins that are already plentiful in the average person’s diet, so their widespread inclusion in these drinks is almost completely unnecessary, said Valerie Tarasuk, the lead author of the study and a nutrition science professor in the faculty of medicine at the University of Toronto.
“It’s very hard to figure out the logic the manufacturers are using to do this fortification,” she said. “There’s no way that the things that are being added are things that anybody needs or stands to benefit from.”
Sugary drinks were just as likely to be concentrated with vitamins as those that were sugar-free. Dr. Tarasuk said that as sugar has become the focus of public health concerns about beverage consumption, “this extreme micronutrient addition has fallen under the radar.”
In nature, there are checks and balances that prevent overconsumption of vitamins and antioxidants, she said. It is hard to ingest too much niacin, for example, by eating whole foods like mushrooms, fish or avocados, which are natural sources of niacin that come bundled with fiber, protein and fat. But someone can easily exceed the daily recommendation for niacin with a single bottle of “formula 50” Vitaminwater, which contains 120 percent of the daily value for it (along with 120 percent of the values for vitamins C, B6, B12 and pantothenic acid).
“You couldn’t possibly get that much from any natural foods,” Dr. Tarasuk said. “That’s concerning to me as a nutrition scientist because we don’t know what the effects of chronic exposure may be. With these products, we’ve embarked on a national experiment.”
A nationwide study carried out by the National Institutes of Health in 2012 found that Americans who take vitamins and supplements were already getting large amounts of nutrients from their food, and on top of that they had the lowest prevalence of vitamin deficiencies to begin with. The study found that supplement use put these people at increased risk of potentially excessive consumption of folic acid, calcium, iron, zinc, magnesium and vitamins A, C and B6.
Added vitamins may clearly aid some people, including women who are pregnant or lactating, or those with specific nutritional deficiencies. But for much of the general population today, there is no scientific justification for a high intake of vitamins and minerals, said Mara Z. Vitolins, a registered dietitian and professor of epidemiology and prevention at Wake Forest Baptist Medical Center.
When consumed in excess, some water-soluble vitamins like B and C are excreted in the urine. But fat soluble-vitamins – including A, D, E and K – accumulate in tissues, posing potential risks.
“These fat soluble vitamins are very stable,” she said. “They’re not released in the urine. If you are over-consuming them, you can raise your levels gradually over time and get into trouble with liver function. You have to be very careful with them.”
Data from clinical trials have highlighted clear risks from excess. A large study published in JAMA in 2009, for example, looked at clinical trial data on more than 6,000 heart disease patients who were treated daily with either B vitamins or placebo over a seven year period. The study found that those who were given folic acid and B12 had higher mortality and cancer rates.
In 2012, a review of 78 clinical trials involving 300,000 people that was published in the Cochrane Database found that antioxidant supplements like beta carotene, vitamin A and vitamin E actually increased mortality. A year later, the United States Preventive Services Task Force concluded that there was “limited evidence” that taking vitamins and minerals could prevent cancer and cardiovascular disease.
The task force noted that two clinical trials had found “small, borderline” reductions in cancer incidence in men who took multivitamins. But the group also said there was good evidence that high doses of antioxidants could cause harm.
The federal food fortification program in the United States began in the early 1900s with the goal of addressing urgent and established nutrient deficiencies. Research showed, for example, that women in their childbearing years were not getting enough folic acid. Since bread and cereal were staples of their diets, folic acid was added to these foods – and as a result the rate of neural tube defects in infants has fallen significantly.
Before 1920, iodine deficiencies were common in some parts of the country. A lack of iodine can lead to goiters, miscarriage, congenital abnormalities and severe learning disabilities. So the widespread fortification of salt with iodine was started in 1924. In the 1930s, vitamin D deficiency was linked to rickets. That discovery led in 1933 to the fortification of milk with vitamin D.
Other foods were enriched with additional nutrients – niacin and iron were added to flour, for example – in the decades that followed.
But in most if not all of these cases, there was a compelling scientific reason for doing so.
“The reason behind the fortification program was to bring our nutrient intake to a reasonable place, and it targeted nutrients that we were lacking,” Dr. Vitolins said.
Early on, fortification was limited to a few select foods, in part so the program would not create nutritional imbalances. In an attempt to prevent indiscriminate fortification, the Food and Drug Administration proposed restricting the number of foods that could be fortified to eight, and it specified which nutrients could be added.
But that proposal was shot down in the 1970s, and over the years Congress went on to restrict the F.D.A.’s authority over fortification and dietary supplements. This helped open the door to the eventual explosion of vitamin enhanced beverages and sports drinks, which today account for sales of more than $18 billion a year in the United States alone.