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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Vitamin Supplements: Are They for Everyone?

October 10, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Better take your vitamins — they're good for you!

When I was a kid, I remember hearing these words from my mother and in TV commercials. It seemed like good advice, yet not all my friends were taking vitamins, and they seemed healthy. That got me wondering: Are they really good for you? Which ones are best and how much is enough? Could they be harmful?

In recent years, recommendations to take various vitamins (and other supplements) are so commonplace that I often see patients who are taking six, eight or even more vitamins each day.

The term "vitamin" comes from "vita" (meaning life) and "amine" (a type of compound that includes some vitamins). There are 13 well-accepted vitamins (see below). Vitamins are not the same as essential minerals, which are also vital to life. Vitamins are compounds or molecules, while minerals are made up of a single element.

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Who Needs Them?

By definition, everyone needs vitamins. And yet, for many people — perhaps most people — taking a daily multivitamin is a harmless but, medically speaking, wasteful expense and effort. One notable study found that average, healthy people taking a multivitamin each day were no healthier and lived no longer than healthy people who took no vitamins.

Because vitamins are needed only in small amounts, most people get more than enough from what they eat. For some, however, getting supplemental vitamins is truly vital, either because of people's choice of foods or because they are unable to absorb and digest one or more vitamins.

Then again, taking too much of certain vitamins can actually be dangerous. The trick is sorting out who should take vitamin supplements to avoid illness and for whom it is unnecessary.


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Water Soluble vs. Fat Soluble Vitamins

Most experts and textbooks divide vitamins into those that dissolve readily in water and those that dissolve in fat. This is helpful because the body handles water and fat quite differently.

Water-soluble vitamins are readily absorbed from the intestine and used by the body; any extra tends to be removed quickly in the urine. Most must be replenished regularly from dietary sources.

Fat-soluble vitamins offer more of a challenge. Certain people have medical conditions that cause problems with absorbing fat-soluble vitamins. Despite adequate dietary intake, they need extra. On the flip side, fat-soluble vitamins are stored in body tissues (such as the liver) and released very slowly over time. As a result, taking too much can be dangerous.

The 13 major vitamins include the water-soluble vitamins (thiamin, riboflavin, niacin, B6, folic acid, B12, pantothenic acid, biotin and C) and the fat-soluble vitamins (A, D, E and K).

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Who Should Take What?

When there is clear evidence of a vitamin deficiency, treatment decisions are generally easy. But when it comes to routine use of vitamin supplements, experts have come to different conclusions. And people often ignore expert recommendations anyway, taking vitamins that no medical provider has suggested and not bothering to take ones that may have been suggested as a preventive measure.

There is reasonable scientific evidence to support the regular use of certain vitamins by:

  • Pregnant women — A daily prenatal vitamin is part of routine obstetric care. Probably the most important component is folic acid (or folate), which can markedly reduce the risk of certain birth defects (including neural tube defects). In fact, women of child-bearing age who might become pregnant are encouraged to take folic acid even before pregnancy. 
  • Perimenopausal women — Vitamin D (along with calcium) is recommended to prevent osteoporosis and other bone disease, particularly if dietary sources are not adequate.
  • People with heart and blood vessel disease — Folic acid may be recommended for people with high homocysteine levels. However, screening homocysteine levels and treating with folic acid to lower risk is unproven.
  • Vegetarians — A multivitamin is recommended because certain vitamins, such as B12, are available only from animal sources. Strict vegans are particularly at risk. Riboflavin (vitamin B2), vitamin D and vitamin A are also concerns for those avoiding meat or animal products. One daily multivitamin will provide enough supplementation for all of them.
  • Smokers and heavy alcohol drinkers — Extra vitamin C and folic acid may reduce the risk of disease among smokers and alcoholics. In addition, people who drink excess alcohol are more prone to thiamin (vitamin B1), pyridoxine (vitamin B6) and riboflavin deficiencies. A daily multivitamin provides inexpensive nutritional insurance.
  • The elderly — Because poor nutrition is common in this group, especially those who are sick and frail, vitamin deficiency is also common. A multivitamin is often recommended to prevent complications from deficiencies in vitamin D and B vitamins.

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Vitamins for Specific Conditions

Anyone with a specific vitamin deficiency should take measures to replenish it. Deficiencies may be detected when symptoms develop or when laboratory abnormalities are noticed in routine testing. Some of the more common vitamin deficiencies include:

  • Vitamin B12 — Low B12 may cause megaloblastic or "pernicious" anemia, difficulty sensing the position of the feet or legs, and, eventually, dementia. In children, it can cause growth problems. In pregnant women, B12 deficiency is a cause of birth defects. 
  • Folate (or folic acid, another B vitamin) — Too little can cause anemia. Low levels are also associated with increased homocysteine, a potential risk factor for heart and blood vessel disease.
  • Vitamin C — Deficiency is called scurvy, which affects many parts of the body, including bones, teeth and blood vessels. Symptoms include fatigue, weakness, rash, irritability and muscle aches. Severe and longstanding deficiency can lead to bleeding, poor wound healing and death.
  • Vitamin D — In children, deficiency of vitamin D causes rickets, a condition marked by deformed bone growth. In adults, the condition is called osteomalacia (literally, bone softening), which causes bone pain and weakened bones that fracture more easily than normal.
  • Vitamin B1 (thiamin) — In developed countries, this deficiency is most often is associated with alcoholism and poor nutrition. Symptoms include confusion, eye problems and imbalance. In developing nations, thiamin deficiency may cause heart failure and muscle weakness.

If you have any of these symptoms, talk to your doctor about their cause, including the possibility of a vitamin deficiency.

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Too Much of a Good Thing?

While intake of vitamins through diet or supplements is vital to life itself, there are limits. Consider the following potential consequences of long-term "megadose" vitamin therapy:

  • Vitamin A — Liver damage, blindness, bone fractures and death
  • Vitamin D — Kidney stones, kidney failure, weak muscles, bone pain, loss of appetite, vomiting and mental changes
  • Vitamin B3 (niacin) — A flushing sensation, diarrhea, vomiting and liver damage
  • Vitamin B6 — Nerve damage
  • Vitamin C — Headaches, diarrhea and kidney stones

Some vitamins may interact with medications you may be taking. An important example is vitamin K, which counteracts the blood thinner warfarin (Coumadin). If you are taking warfarin to prevent stroke, taking extra vitamin K could offset that benefit, increasing your risk of stroke.

In the absence of a specific disease or condition that warrants it, there is risk without clear benefit related to taking high doses of vitamins. Even "regular" doses of some supplements may impair health: Studies have noted that the use of beta carotene (a precursor of vitamin A) is associated with a higher risk of cardiovascular disease and some cancers.

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Vitamins for All?

Increasingly, experts are recommending that all adults take a multivitamin each day as "insurance" against vitamin deficiency. Folate also may lower risk of breast and colon cancer and birth defects. Vitamin D may lessen the risk of osteoporosis and osteomalacia.

For women of childbearing age who might become pregnant, experts recommend 400 to 800 micrograms per day of folic acid. A higher dose may be recommended if a previous child had a neural tube defect.

It's likely that ongoing research will spell out which vitamin supplements are most important and who should take them. Until then, things are likely to remain pretty confusing.

Consumers are deluged with recommendations to take lots of vitamins. Much of this promotion comes from people or companies trying to sell their products, or from studies that may be preliminary or even contradict other research.

It's enough to make your head spin — and there's no good vitamin you can take for that!

Do you really need to take your vitamins? Probably not, especially if you are healthy and already get at least five servings of fruits and vegetables each day.

But if you are concerned that your diet might not meet your vitamin needs, change your diet and take a single daily multivitamin. It should be inexpensive and contain 100% of the recommended daily allowance of the 13 major vitamins. While this might not be absolutely necessary, the minimal cost and risk might just be worth the peace of mind.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.


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