What is a multivitamin?

In one line

A multivitamin is a supplement that combines many vitamins and minerals in one pill, with no fixed recipe, so every product is different.

What is a multivitamin?
The 'one pill' you always see in the supplement aisle
Every supplement aisle has 'multivitamins', with long lists of vitamin and mineral names on the label. What is inside, and how do you read the label? Does taking one really make you healthier? This post goes through it step by step.
In one line
A supplement that combines many vitamins and minerals
A multivitamin is a supplement that combines many vitamins and minerals in one pill. In Korean it is also called a 'combined vitamin'. It is sometimes written 'multivitamin/mineral' to show that minerals are included too.
Vitamins and minerals
Nutrients you need only in tiny amounts
Vitamins are substances the body needs to grow and work properly; humans need 13 of them. Minerals are elements the body needs, like calcium, iron and zinc. Both are needed in very small amounts, so together they are called 'micronutrients'.
No fixed recipe
Each product has different contents and amounts
There is no scientific or legal definition of a 'multivitamin'. So products differ widely in how many nutrients they contain and how much of each. Calcium, for example, is plentiful in some products and present only in small amounts in others.
Reading the label
'%DV' is the share of the daily value
US supplement labels list each nutrient and its amount per serving. The '%DV' next to it shows what percent of the daily value that amount is; 100% means the product holds a full daily value. However, the amount actually inside often differs from the amount on the label.
Why people take it
About one in three US adults
About one in three US adults takes a multivitamin. The reasons people most often give for taking supplements are 'to stay healthy' and 'to fill nutrient gaps in my diet'.
Food comes first
A varied diet is the best way to get vitamins
The best way to get enough vitamins is to eat a wide variety of foods. Supplements are another way to fill a gap when food falls short. For example, pregnant people take a vitamin called folic acid to prevent certain birth defects in the baby.
Doubling up
The same nutrient can go over the upper limit
The 'upper limit' is the daily amount above which the risk of harm goes up. A US National Institutes of Health expert panel named it a safety concern that people go over this limit by stacking a multivitamin with other supplements and fortified foods. Vitamins A, D, E and K in particular build up in the body.
Products with iron
Dangerous if a child swallows them
Iron-containing supplements can be deadly if a child swallows too many. That is why the US requires iron-containing supplement pills to carry the statement that accidental overdose is a leading cause of fatal poisoning in children under 6, along with a warning to keep them out of children's reach.
A common misconception
Does a multivitamin help you live longer?
No result showed that. Pooling trials in adults without nutrient shortages, multivitamins did little or nothing for heart disease and death, and lowered cancer only slightly (about 7%). A large study that followed people for more than 20 years also found that daily users did not have a lower risk of death.
Summary
Many nutrients in one pill, a different mix in each product
A multivitamin is a supplement that combines many vitamins and minerals in one pill; there is no fixed recipe, so every product differs. When adults without nutrient shortages took them, no result showed a longer life. Related terms: micronutrients, upper limit, %DV.