The limits of nutritional supplements: they don’t cure or prevent ailments, nor are they harmless

On the shelves of a pharmacy, every bottle makes a promise: “Energy and vitality.” “Immunity.” “Prostate comfort.” Boxes of pills – or “nutritional supplements” – guarantee that they can reduce “oxidative damage” while boosting “sexual desire” and “fat burn.”

A few feet away, on the shelves of a supermarket, the pattern is repeated: multivitamins, minerals and various combinations of herbal extracts are offered for “joint well-being” or to help the consumer achieve “detoxification” or “extra vitality.” However, the scientific community views all of these promises with suspicion, cautioning that there’s a lot of marketing at play, rather than actual effectiveness. These supplements don’t cure or prevent diseases… and they’re not harmless, either.

Nutrition experts warn of the limitations of these products and point out that – beyond those who suffer from specific diagnosed nutritional deficiencies – nutritional supplements lack effectiveness in treating conditions or preventing the appearance of ailments. In the worst cases, these concoctions can even pose certain risks to one’s health, if ingested without supervision, or if quantities higher than the maximum recommended amount are consumed.

In the eyes of the law, many of these supplements are classified as foodstuffs, not drugs. And, foods that are intended to complement (not replace) a normal balanced diet, these supplements include vitamins, minerals (such as calcium or magnesium) and probiotics. They can also be amino acids – such as glutamine – or compounds derived from plants, such as caffeine or ginseng. Unlike medicines, food supplements don’t require authorization for sale and can be dispensed in any location where food is sold, from a pharmacy to a supermarket. But Azahara Nieto – a dietician and nutritionist – warns that, no matter how natural they are or may seem, “they’re not harmless.” And furthermore, he emphasizes: “If your diet is complete, you don’t need supplementation.”

Experts note that it doesn’t make sense to resort to certain food supplements unless a nutritional deficiency is detected. “There are primary deficiencies, when a nutrient isn’t in the diet, as well as secondary deficiencies, in which a nutrient – despite being present in the diet – for whatever reason doesn’t metabolize well. It doesn’t end up [being absorbed] and must be provided through other means,” explains dietician Juan Revenga.

Obese people undergoing bariatric surgery, for example, require vitamin and mineral supplementation. Vitamin B12 supplements are also recommended for individuals who follow a strict vegetarian lifestyle. Another supplement that may be needed – according to Jordi Salas-Salvadó, professor of Nutrition at the Rovira i Virgili University of Tarragona – is folic acid in women who wish to become pregnant. “A folic acid supplement is recommended to prevent neural tube alterations in the baby.” A neural tube defect can cause problems in the nervous system, such as spina bifida. According to scientists, iron supplementation in pregnant women also serves to prevent premature birth or low birth weight in those who are at risk of deficiencies.

The weight of marketing

In practice, however, the phenomenon of dietary supplements goes beyond necessity. A survey published in the Spanish Journal of Human Nutrition and Dietetics revealed – after surveying 2,630 Spaniards – that 70% of the population studied had taken some form of supplement in the last year, whether food supplements, plant extracts, products for athletes or pills to lose weight. In the United States, a health survey reported that more than half of Americans had taken a dietary supplement in the previous month. The majority claim that they take them to improve their health, their sports performance, or to lose weight. “There’s a lot of marketing and a tendency to supplement poor management of daily nutrition with supplements. To compensate for this, we believe that the supplement makes up for the situation caused by our habits,” says Violeta Moizé, a dietitian and nutritionist at the Hospital Clínic of Barcelona.

But there are no miracles to be found in those pills. “They’re products that contain concentrated substances that we can find in food,” Revenga insists. This is particularly the case in Western countries, where there’s “a beastly food availability” – there are no shortages of any food. “These products are marketed because people want to be deceived. On those little boxes, it says ‘more energy, less fatigue, more vitality’ and that’s attractive to us. Pseudo-miraculous properties are transferred to these prfoducts,” the dietician sighs. But magic recipes don’t exist. “Vitamin D is related to the immune system, but taking more vitamin D won’t make us more immune to COVID. We can only have an immune system within [the boundaries of] our human nature – we won’t be superheroes,” he emphasizes.

According to scientific literature, beyond the few cases that have been identified and reviewed by health professionals, food supplements have a limited scope. The intake of vitamin and mineral supplements among healthy people doesn’t reduce the risk of diseases, nor are weight loss supplements an effective method against obesity. Nor do omega-3 fatty acids – which can help reduce triglycerides – have a clear and forceful impact on the prevention of heart ailments.

Last year, a U.S. Preventive Services Task Force (USPSTF) review of the role of dietary supplements in disease prevention concluded that “Vitamin and mineral supplementation was associated with little or no benefit in preventing cancer, cardiovascular disease and death, with the exception of a small benefit for cancer incidence with multivitamin use.”

Following its analysis, the USPSTF advised against the use of beta-carotene or vitamin E to prevent cardiovascular disease or cancer, concluding that the available evidence is insufficient to calculate the risk and benefit of taking other nutritional supplements to prevent these diseases. Regarding these conclusions, scientists from Northwestern University wrote an editorial in JAMA, in which they warned: “The most common reason why people report taking supplements is to improve or maintain general health. However, whole fruits and vegetables contain a blend of vitamins, phytochemicals, fiber, and other nutrients that likely act synergistically to provide health benefits. Isolated micronutrients may act differently in the body than when naturally packaged with a host of other dietary components.”

On the other hand, since these products are considered food rather than drugs, “they have no obligation to prove what they say they do,” Revenga warns. They don’t require a medical prescription, either. Any individual can consume them on their own… although these products are by no means risk-free.

The dangers of consuming excessive amounts of vitamins

To begin with, one of the dangers is the control of quantities. “If you eat healthy and take a multivitamin, maybe you’re overdoing it,” Revenga notes. The dietician points out that there are recommended maximum daily intakes for all nutrients and, if these limits are exceeded, one may experience “toxic or deleterious effects.”

“Many of these nutrients can limit the absorption of other nutrients,” he explains, or interfere with the activity of other organic functions. They can also cause adverse side effects. “If you consume too much phosphorus, you’ll limit [your body’s] calcium absorption. If you take too much iodine, thyroid function can be disrupted. If you take a lot of vitamin D, you can have diarrhea.”

Along these lines, Salas-Salvadó warns that “absorption and bioavailability isn’t the same as when you get your nutrients through food.” He offers another example: “With antioxidants – such as vitamin A, E, or selenium – if we eat a varied diet, we’re consuming various amounts of different antioxidants that are good for health. But if you go overboard and take large amounts [of the vitamins], this can have oxidizing effects. The important thing is to have a balanced diet and consume nutrients in normal physiological doses.”

Nutritionist Violeta Moizé also warns about the danger of “overmineralization.” “You can saturate other channels, because all these micronutrients are cofactors of reactions that occur within our bodies. They’re needed in certain quantities for a function to be carried out… [but], if you exceed the amount, you can saturate [your system].”

With nutritional supplements that incorporate plant extracts, experts draw attention to the lack of studies about their safety. Revenga criticizes the fact that manufactures advertise unproven benefits. “It’s the exotic component that serves the manufacturer on a sales level. It’s putting glitter on it,” he scoffs. In an article published in the International Journal of Environmental Research and Public Health, Polish researcher Regina Wierzejska points out how “recent years have witnessed the appearance of numerous preparations that include plants that have never previously been used in Western medicine. Their mechanisms of action have not been sufficiently investigated and described, while the labels usually fail to include information about the contraindications, which does not mean they do not exist. Herbal components, especially herbal mixes, may have a negative effect on the drug mechanisms of action, both by accelerating excretion from the body or by producing dangerously high concentrations in the blood.”

Adulterated supplements

Another threat is the illegal incorporation of substances that the manufacturer doesn’t identify on the box and the consumer ingests unknowingly. There are substances that can cause adverse effects, or interact with other drugs that the individual is taking. The Spanish Agency for Food Safety and Nutrition (AESAN) closely monitors what are deemed to be “pharmacologically active substances marketed as food supplements,” warning of their presence. This occurs, above all, with compounds that claim to increase sexual vigor, promote muscle development, or accelerate weight loss.

In a study that analyzed the adulteration of dietary supplements to improve sexual function, it was found that the majority contained phosphodiesterase inhibitors, such as sildenafil (present in Viagra). And, in several samples, there was even a dose of these substances well above the maximum approved amount recommended in drugs. “This is an adulteration that’s especially dangerous when a person takes medication, for example, to control blood pressure,” Revenga says. And the same thing happens, he adds, with “natural” slimming products, which incorporate antidiabetic active ingredients. Last year, the AESAN launched three alerts regarding the presence of active ingredients similar to those used in the manufacturing of Viagra in food supplements, along with another warning about an anti-obesity drug in a supplement that was presented as a “natural product.”

“The word ‘natural’ is a key that opens many doors. A snake bite or a volcanic eruption are also natural,” Revenga jokes. Experts urge that caution be exercised when it comes to the consumption of these substances. The nutritionist Azahara Nieto recommends that, before making any decision, people should “review their diet to see what they need… and not self-diagnose or self-prescribe anything.” It’s always best to consult with your family doctor or other health professional… and to be weary about miraculous promises.

“There’s a lot of marketing out there. Advertisements are made for things that are backed up by no evidence [and there’s] no mention about the unwanted effects they may have,” Salas-Salvadó affirms. In its recommendations, the AESAN warns that “natural does not mean safe, help for weight control only makes sense [when accompanied by] a healthy lifestyle, sports performance requires adequate training and a healthy diet… and no food supplement is useful when it comes to sexual relations.”

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