Vitamins—Are They Really “One Size Fits All?”

From the Lecture Series: Nutrition Made Clear

By Roberta H. Anding, M.S., Baylor College of Medicine and Texas Children’s Hospital

The idea of eating healthy seems to change as often as the seasons. Concerns over fats, sugars, undercooked red meat, carbohydrates, and many others have made news at one time or another. However, vitamins have always remained a constant recommendation. How do vitamins benefit us, and are they a “one size fits all” dosage?

spoon with pills,
(Image: ronstik/Shutterstock)

Even in ancient history, people understood that there was some connection between nutrition, the food that we eat, and health. For example, the ancient Egyptians wrote about the fact that liver could be used to cure night blindness. Although they didn’t understand at the time, it’s because the liver contains vitamin A and they were treating a vitamin A deficiency.

A portrait of Scottish doctor James Lind (1716–1794)
James Lind, a Scottish doctor, discovered that citrus fruit can cure scurvy and that scurvy is a deficiency of vitamin C. Painting by Sir George Chalmers. (Image: Sir George Chalmers/Public domain)

Nutrition entered the scientific era in 1747 when ship’s surgeon James Lind conducted what is considered to be the first modern medical experiment. He discovered that citrus fruit can cure scurvy and that scurvy is a deficiency of vitamin C—although vitamin C wasn’t discovered until 1920. Lind did a controlled experiment where he fed citrus fruit to sailors suffering from early signs of scurvy. He compared that to vinegar and also to a weak acid. He thought maybe it was acid that was deficient in scurvy. It turns out that the sailors who received the citrus fruit did much better and were cured of their symptoms of scurvy.

This is a transcript from the video series Nutrition Made Clear. Watch it now, on Wondrium.

What is a vitamin?

In the early 1900s, chemists were busy identifying various substances that would cure nutritional diseases. It was Polish biochemist Kazimierz Funk who proposed the name vitamine, which was a combination of the words vital and amine. However, later it was learned that not all vitamins contained a chemical group called an amine. Therefore, that final “e” was dropped and we’re left with the word vitamin.

Photo of Polish biochemist Kazimierz Funk scanned from Wielka Encyklopedia Powszechna PWN, Warsaw, Poland, 1964, vol. 4, page 55/
Polish biochemist Kazimierz Funk proposed the name vitamine, which was a combination of the words vital and amine. (Image: Unknown photographer/Public domain)

Specifically, vitamins are those nutritional substances that are essential to health in tiny amounts, but which an organism cannot manufacture in sufficient quantities for themselves. Therefore, we have to get vitamins from food by definition. Of course, which substances are vitamins depends on the species. Human beings, for example, need to get vitamin C from food but most other mammals can make vitamin C toward themselves.

Vitamins are also defined by what they do. Most vitamins are actually a group of compounds or chemicals that all have the same biological activity. The majority of vitamins are cofactors for enzymes, which means they help biochemical reactions occur. Some vitamins, like vitamin D, also have some hormone-like properties.

Learn more about where to find credible sources of information on nutrition

Vitamin Classifications

We also classify vitamins based on their solubility. Water-soluble vitamins—vitamins C and the B vitamins—are soluble in water and will be quickly excreted in the urine. If you eat more than your body needs over a short time, you’ll just get rid of the extra. However, vitamins A, D, E, and K are all fat-soluble vitamins. That means that they are stored long-term in the fat of your body. This also means that to be deficient in this vitamin, you have to have a deficiency in your nutrition, usually over a long period of time.

Do We Need Vitamins?

This brings us to our first big vitamin myth—that routine vitamin supplementation or taking a daily vitamin is important for everyone’s health and wellbeing. There is no evidence for any health benefit of routine supplementation. This is, admittedly, a very difficult question to answer if you want to know if there are long-term health advantages to vitamins over decades. Those studies are very difficult to do.

A Swedish study looked at hundreds of thousands of people from different clinical trials. They found no correlation between those who routinely supplemented with vitamins and health outcomes.

However, observational studies have been done. The biggest is a Swedish study that looked at hundreds of thousands of people that had enrolled in various clinical trials. They found no correlation between those who routinely supplemented with vitamins and health outcomes. In fact, there was a slightly increased risk of death among those who supplemented. No one interprets this study as establishing cause and effect. It could be—and is probably true—that people who are taking vitamins are doing so because maybe they’re not as healthy, to begin with, and that’s why their outcomes weren’t as good.

But, if we look at all the research that we have, experimental or observational, there is no evidence to back the claim that routine supplementation is important for health. For most people, eating a balanced diet is enough. Further, studies that show health advantage or a good outcome based on nutrition are only able to link those advantages to eating healthy foods—not to taking supplements. Therefore, we come back to the conclusion, based on the evidence, that the best thing to do is to have a healthy diet full of fruits, vegetables, and variety.

We come back to the conclusion, based on the evidence, that the best thing to do is to have a healthy diet full of fruits, vegetables, and variety. Click To Tweet

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Specific Situations

There are many special situations to consider. When routine supplementation is referred to, we’re talking about in a healthy person with no medical conditions. What about sub-populations? Let’s, for example, first go to children. Children certainly do have increased nutritional needs because they’re growing. Should we routinely give children vitamin supplements? It’s probably still the best recommendation, based on the evidence, that what’s most helpful for growing kids is that they have a healthy diet. In fact, you should get children in the habit of eating lots of fruits, vegetables, and a generally varied and healthy diet, even from a young age.

However, it can be difficult to get them to eat their vegetables and to get them to eat a variety of things. If your children do have a restrictive diet despite your best efforts, it is reasonable to consider supplementation as nutritional insurance.

Pregnant women looking at vitamin supplements
Prenatal vitamins are routinely recommended for pregnant women and women who are trying to get pregnant. (Image: Syda Productions/Shutterstock)

Pregnancy is another situation in which there are increased nutritional demands. Pregnant women have incredibly high nutritional demands. It is routinely recommended for pregnancy—and for women who are planning on possibly becoming pregnant—to take a prenatal vitamin because you need to boost your nutritional reserves before you know that you are pregnant. Specifically, folic acid is important, as mentioned earlier. Supplementing with folic acid reduces neural tube defects like spina bifida.

Vegetarians also have special nutritional needs because they have chosen to narrow the range of foods that they will eat. You can get everything you need from a vegetarian or vegan diet, but you have to know what you’re doing and you have to be very careful. Vitamin B12 specifically can be a problem because a lot of the B12 in our diets comes from animal sources. If you are choosing to eat a vegetarian or vegan diet, be careful that you’re eating foods that contain a lot of B12. You may have to have your B12 levels checked and supplement if necessary.

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Specific Vitamins

Vitamin D insufficiency and deficiency is, increasingly, being recognized in Western and developed countries. As many as two-thirds of the population in recent studies are vitamin D insufficient—not the kind of deficiency that would cause rickets, but not getting as much vitamin D as they should.

Most of our vitamin D does come from exposure to sunlight. The vitamin D gets manufactured in reaction to exposure to the sun. For the average person, 15 minutes of sunlight exposure per day is sufficient to meet your vitamin D needs. However, that’s an average person. This will vary based on your latitude, where you are in the world. People in Florida, for example, don’t need as much sun exposure as those living in Alaska.

It also depends on your pigmentation, how dark-skinned you are. The darker your skin, the more sunlight you need. There is also the time of year—people tend to become relatively insufficient in vitamin D during the winter months and have more vitamin D during the summer months. Therefore, for more people than we had previously thought, it may be necessary to supplement vitamin D if you’re not getting enough from sunlight and fortified foods.

Calcium is another special situation. Adult women, especially those approaching menopause, may need to supplement calcium and vitamin D to optimize bone density and prevent osteoporosis. Osteoporosis is a relative decrease in the calcium content of bones. Once women go through menopause, they steadily lose bone content; it’s important to build up as much bone density as possible before menopause. The ways to do that are with supplementing calcium, perhaps vitamin D, and of course, with weight-bearing exercise. That’s important as well.

Blood sample with requisition form for vitamin B12 test
As you age, a primary care doctor will check routinely to make sure your vitamin B12 levels are sufficient. (Image: Jarun Ontakrai/Shutterstock)

Vitamin B12 is another one that deserves special consideration. As we age, we have a decreased capacity to absorb vitamin B12 just from our food. B12 can’t be passively absorbed like most nutrients in food; it needs to be actively carried into our blood system from the food. That system can decrease as we age. Many people become relatively or absolutely vitamin B12 deficient as they get older. A primary care doctor will check your levels routinely to make sure your vitamin B12 levels are sufficient.

If they are on the low side, oral supplementation is enough for most people to replenish B12 supplies. However, if the ability to absorb the B12 has decreased too much, you may need monthly vitamin B12 injections to keep your levels up in the normal range.

Learn more about some of the myths associated with B-vitamin nutrition


While vitamins are, by definition, essential to nutrition to prevent deficiencies and improve many medical outcomes, we need to avoid the myth that if some vitamins are good, then more must be better. This has led some to recommend very high doses, called megadoses of vitamins. However, there is no theoretical reason, nor is there any evidence, to support the safety or the health effectiveness of megadosing. It is not recommended.

We need to avoid the myth that if some vitamins are good, then more must be better. Click To Tweet

Many water-soluble vitamins, such as vitamin C, will be simply excreted in your urine if you try to megadose. It is not as dangerous as the fat-soluble vitamins, but it is a waste of time and money. High doses of vitamin E, for example, which is a fat-soluble vitamin, have been shown to correlate with an increased risk of heart disease. Aside from the notion of overdosing toxicity, regularly supplementing with high doses of certain vitamins actually correlates with an increased risk of certain diseases.

The best advice is to keep it simple. Don’t get overwhelmed with the complexity of all the different types of nutritional advice that people are willing to give. A few simple rules are enough. Eat a variety of foods, plenty of fruits, and vegetables. For most people in most situations, you will be fine. You will be in perfect health in terms of your nutrition.

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Common Questions About Whether Vitamins Really Work

Q: Should you take a multivitamin?

The evidence for multivitamins is mixed. They contain much filler and things the body does not need even as a supplement. As a replacement for not eating well, they are largely derived synthetically; real food is real medicine. However, some studies have suggested that a 35 percent decrease in heart disease in women but not men, was due to multivitamin use.

Q: Are vitamin supplements dangerous?

Daily vitamin intake of vitamin supplements in otherwise healthy people is not advised. There have been links between iron, vitamin A, and vitamin E supplements and increased risk of death, heart failure, and weakened bones.

Q: Do vitamins damage the liver?

Vitamin A is most commonly given to people with liver disease and can help; however, it can also damage the liver in large doses.

Q: Are vitamins eliminated from the body in urine?

Fat-soluble vitamins such as D can be stored while water-soluble vitamins are not stored and any excess will be eliminated via your urine.

This article was updated on June 1, 2020

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