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Dietary supplements and multivitamins are a thriving multi-billion dollar industry, but studies show they have little, if any effect on the health of those who are not nutrient-deficient or pregnant.
In North America, experts valued the market size of dietary supplements at $52,874.7 million in 2021, with annual spending expected to increase by 5.6% until 2030.
According to a survey conducted between 2011–2014, 52% of adults take at least one dietary supplement every month, and 31% use a multivitamin-mineral supplement. The most common reason for taking supplements was “overall health and wellness to fill nutrient gaps in the diet.”
It also found that beta carotene supplementation among healthy individuals was linked to an increased risk of lung cancer.
Medical News Today spoke with five nutrition experts to understand more about how multivitamins affect health, and why they may not be the “superheroes” of self-care.
What are multivitamins?
“Strictly speaking, the term ‘multivitamins’ refers to supplements containing only vitamins,” Dr. Sarah Berry, chief scientist at ZOE, and reader in nutritional sciences at King’s College London, told MNT. “However, most supplements contain a mixture of vitamins, minerals and other nutrients such as omega-3 fatty acids.”
The first multivitamins emerged in the early
- basic or broad-spectrum — taken once per day, they contain all or most vitamins in quantities that do not exceed
daily values (DVs), recommended dietary allowances (RDA), and adequate intakes (AIs)
- high potency — containing vitamins and minerals that are substantially higher than DVs, RDAs and AIs, or even the
tolerable upper intake level (UL)
- specialized — combining several vitamins and minerals for a specific purpose, such as boosting energy, weight control, or improving immune function. Some of these products might contain amounts of nutrients substantially above the DV, RDA, AI, or even UL.
As multivitamins have no standard regulatory definition, their nutrient contents and quantities vary widely between products.
When asked about the most common misconceptions about multivitamins, Dr. Rachel Kopec, assistant professor of human nutrition at The Ohio State University, told MNT:
“One of the biggest misconceptions is the dose delivered. The bioavailability — the percentage of a given micronutrient dose that is actually absorbed into the bloodstream — from multivitamins can be quite low for fat-soluble micronutrients like vitamins A, D, E, K, and essential minerals such as iron and calcium, depending on how they are encapsulated, and what they are encapsulated with. For example, there is a risk for iron oxidizing vitamin A once dissolved in the stomach.”
To the same question, Dr. Berry noted that more does not always mean better.
She noted that “[s]ome of the mega-dose supplements sold are not only very expensive but have doses way beyond which our body needs or can even process, so most of it gets flushed down the toilet.”
Prof. Edward Giovannucci, professor of nutrition and wpidemiology at the Harvard T.H. Chan School of Public Health agreed with Dr. Berry that more does not always mean better, although he told MNT that multivitamins at around RDA levels might nevertheless help compensate for suboptimal diets.
He noted, however, that this does not mean that multivitamins should replace a good diet: “Another misconception may be that there is something special you can get from multivitamins that you can’t get from a good diet. A possible exception is vitamin D, which is low in the diet and we get most from the sun. So if we avoid the sun, we may not be getting enough from the diet.”
Dr. Phillip Calder, professor of nutritional immunology at the University of Southampton also explained for MNT that:
“Multivitamin supplements are not a replacement for eating a healthy diet and cannot be used to mitigate the effects of an unhealthy diet. They can be used to make up nutrient gaps if a person’s diet does not fully meet their requirements, but dietary strategies should come first.”
Dr. Berry noted that there is a lot of miscommunication about the health effects of supplements. This, she said, is due to two factors.
The first is the large variation between multivitamin products making them harder to study. The second is that individual micronutrients may not affect the body in the same way as when consumed as a part of a fruit or vegetable.
“The health effects of nutrients are largely extrapolated from studies using food interventions,” she explained. “However, the impact of a nutrient from a food is modulated by the other nutrients in the food as well as the complexity of the food matrix — the structure of the food.”
“Therefore, some of the claims that ‘x’ supplement will improve ‘y’ health outcome are not yet proven using the supplement alone and are often extrapolated from a dietary study where so much else is also coming into play,” she continued.
She added that many claims that multivitamin manufacturers make lack evidence — especially those targeting different ages, sex, and mental health profiles and those that promise to make one “look younger” or “more brainy.”
However, she also pointed out that some supplements with “bioactive” ingredients, such as certain polyphenols, may have more targeted effects on health.
From her research, known as the ZOE PREDICT studies, she noted that the effects of food on health depend not just on what we eat, but also on “who we are” and “how we eat.” She said:
“ZOE PREDICT has demonstrated the association between how much sleep we have, the time of day that we eat, and the order in which we eat our food, and various health outcomes. How we respond to food is also shaped by who we are, including our microbiome, age, sex, body composition, genes, and so much more, which explains why each and every one of us responds so differently to food and nutrients.”
Who should take multivitamins
Dr. Brian Lindshield, professor in the Department of Food, Nutrition, Dietetics, and Health at Kansas State University, told MNT that people who may develop a micronutrient deficiency should take multivitamins.
Accordding to him, “[t]aking a multivitamin can make up for consuming a micronutrient-poor diet.”
“It can help prevent micronutrient deficiency, which is important, but the reason that many people take them is they want the health benefits of a micronutrient-rich diet — such as chronic disease reduction — without having to consume the micronutrient-rich diet. But research has found that multivitamins — or single micronutrient supplements — have little to no benefit on chronic disease risk,” he noted.
Dr. Kopec added that older people should also consider taking multivitamins. “Eating is a social activity,” she said, “and in the U.S., many older adults live alone.”
“They also have physical mobility limitations restricting their ability to carry groceries or to cook, and can have dental disease or false teeth that make chewing difficult, etc. With age, we are also fighting biology, with reduced ability to absorb B12, and reduced stomach acid which limits iron and calcium uptake,” she continued.
“Together,” explained Dr. Kopec, “these factors put older adults at risk, and multivitamins can fill an important gap. Additionally, individuals following an exclusively plant-based diet, parents of picky children, and those with certain health conditions can also benefit from a general multivitamin.”
Prof. Giovannucci added that a multivitamin with folic acid may
He also noted that specific conditions might also make multivitamins an option. For example, those who are pregnant may need higher nutrient intake, as well as those with conditions that may reduce the body’s ability to absorb certain nutrients, such as celiac disease and ulcerative colitis.
Dr. Berry added that iron supplements might also be recommended for women, especially as over a quarter of females in the United Kingdom have iron deficiency anemia. She further noted that long-chain omega-3 supplements may benefit those who do not consume fish or who follow a vegetarian or vegan diet.
“This is because humans are unable to make omega-3 fatty acids, and we can only convert plant-based sources of omega 3 (linolenic acid) into the omega-3 fatty acids found in fish (eicosapentaenoic and docosahexaenoic acid),” she explained. “In people who do not have adequate intakes, an increase in omega-3 fatty acids found in oily fish has been shown to have favorable effects on many health outcomes, including cardiometabolic health outcomes.”
All of the experts agreed that consuming a well-balanced diet is key. Dr Giovanni said: “The most important things are limiting weight gain, some physical activity, not smoking, avoiding too much alcohol, and a good, balanced diet. The combined effect of these on health is massive.”
“Limiting the adverse effects of stress is important too. Multivitamins would be less helpful for people with a very good lifestyle, except possibly for extra vitamin D,” he explained.
The experts also cited getting good sleep and avoiding ultra-processed foods as important contributors to good health. Dr. Berry noted that “[w]e should also aim to limit ultra-processed foods and, where possible, eat foods in their original form. For example, opt for a whole orange rather than orange juice.”
Dr. Kopec recommends paying attention to food preparation and co-consumption to maximize micronutrient absorption. In particular, she recommended:
- eating fruits and vegetables with healthy fats, such as avocados, and opting for plant-based oils, to absorb fat-soluble vitamins
- cooking orange and deep green leafy vegetables together to improve provitamin vitamin A absorption
- soaking dry grains and legumes in cold water overnight before cooking to best absorb B vitamins and essential minerals.
“Finally, essential minerals are best absorbed from animal products i.e. iron is much more bioavailable from red meat, calcium from dairy products, etc. Just be sure to consume in appropriate portions. One serving of beef is [approximately] 3 ounces (oz), but I’ve never been to a restaurant that serves less than a 6 oz filet!”
– Dr. Rachel Kopec
“For exclusively plant-based eaters, it’s also important to incorporate vitamin B12, which is only found in animal products. Fortunately, in the U.S., it is easy to find B12-fortified nutritional yeast to meet this need — be sure to check the label for ‘cobalamin’ or ‘vitamin B12’ in the ingredients,” Dr, Kopec advised.
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