Multivitamins contain a combination of at least 3 vitamins or vitamins and minerals (and sometimes other ingredients as well).
Other names for these products are multivitamin/multiminerals or MVMs (if they contain both vitamins and minerals), multis, multiples, and sometimes just vitamins.
There is no standard for the nutrients or their levels in multivitamins.
Many are designed to be taken once a day and contain most or all of the familiar vitamins and minerals, generally at levels that are close to the recommended maximum amounts for each nutrient.
Megavitamins (also known as megadose multivitamins and orthomolecular therapy) contain very high doses (sometimes hundreds of times more than the daily requirement) of one or more vitamins or both vitamins and minerals.
(See also Overview of Dietary Supplements.)
Claims for Multivitamins and Megavitamins
Megavitamin companies claim that taking very high doses of vitamins with or without high doses of minerals will increase the amount of nutrients available to help the body stay healthy or achieve higher levels of health.
Proponents of multivitamins and megavitamin have identified several similar benefits of these products:
Promote good health by giving the body micronutrients it needs
Promote a healthy immune system
Support eye health as well as healthy hair and skin
Boost energy levels and feelings of well-being and decrease stress
Treat diseases caused or exacerbated by deficiencies in certain vitamins and minerals
Prevent or treat diseases that are more common in older adults, including diabetes, heart disease, high blood pressure, and declines in brain function.
Evidence for Multivitamins and Megavitamins
Multivitamins can help people get recommended levels of nutrients when foods alone are not providing enough vitamins and minerals.
Studies show that people who take multivitamins regularly are more likely to have adequate levels of needed vitamins and minerals than people who do not take these dietary supplements. But the risk of getting too much of certain vitamins and minerals is also higher in multivitamin users.
Studies have also shown that multivitamin users tend to have healthier lifestyles and diets than people who do not take these supplements. For this reason, it is difficult to tell whether the prevention of chronic diseases and the promotion of good health in multivitamin users is due to their use of these supplements or because they tend to have healthier diets and lifestyles.
Several large studies have found no clear evidence that vitamin supplements can prevent chronic diseases or death due to major chronic diseases in people who do not have any nutritional deficiencies.
Side Effects of Multivitamins and Megavitamins
Taking multivitamins that provide nutrients in amounts that are similar to recommended daily intakes should be safe for most healthy people. However, there are certain risks:
If the multivitamin or megavitamin capsule or pill is very large, older people may have difficulty with swallowing and be at risk of choking.
Drug Interactions with Multivitamins and Megavitamins
Megavitamin supplements can interact with several medications, depending on their ingredients.
Taking a large dose of vitamin C with oral contraceptives or hormone replacement therapy may increase estrogen levels.
Recommendations for Multivitamins and Megavitamins
Although multivitamins can help people get recommended levels of nutrients, it is unusual for people in high-resource countries not to get enough vitamins and minerals to meet their bodies' needs from foods alone. People should ask their doctor about risks for a vitamin or mineral deficiency.
Multivitamins and megavitamins are not recommended for people who do not have any nutrient deficiencies because the claimed health benefits have mostly not been confirmed in high-quality studies, and these benefits are often outweighed by the risks of taking large doses.
Multivitamins containing doses of vitamins and minerals that are similar to recommended daily intakes are probably safe for most people. But supplements, such as megavitamins, containing larger amounts than those recommended can have unwanted effects and can even be harmful.
