Because I’m a dietetic intern, people are constantly asking me for advice. Anybody who hears that I’m in the nutrition field, whether it be on the train, in a grocery store, or that one uncle you talk to once a decade at Thanksgiving dinner, has some sort of question about nutrition. Some of those frequently asked questions are “should I take a multivitamin?” and “how do you feel about _____ supplement?” This is a difficult question to answer without knowing the person’s background. Many people believe that there is a more-is-better approach when taking a supplement, without knowing that most people can actually meet their nutrient requirements through food alone.
It is important to remember that multivitamins are not meant to replace, but instead to supplement nutrients that may be inadequate despite a healthy diet. Guidelines are shaped like a bell curve, so recommendations are simply based off of the middle amount of nutrient most people need. Some people naturally need more nutrients for optimal health depending on the stage of life. For example, pregnant women or women of childbearing age need more folate. Folic acid/folate is beneficial in all populations, but it is especially important in early pregnancy. Women with inadequate folate consumption are at higher risk for conceiving infants with birth defects. Another vulnerable population who may require additional nutrient supplementation includes men and women over age 60. As we age, we may need higher amounts of certain nutrients. For example, seniors absorb vitamin B12 less efficiently and also often have a blunted sense of taste and smell, which may cause lower food and nutrient consumption, making supplementation more necessary.
Increased vitamin consumption is not always better, and in some cases, an excess of certain vitamins may actually cause illness, disease, or even death. Fat-soluble vitamins such as A, D, E, and K can build up in the body and cause toxicity. Many multivitamins contain phosphorous, which most Americans already consume too much of. Similarly, a high amount of magnesium or vitamin C may causes diarrhea and very high doses of niacin can cause liver damage.
Certain vitamins can either decrease or increase bioavailability when paired together. For example, the combination of vitamin C and iron, and vitamin D and calcium, complement each other by increasing the amount of nutrients that can be absorbed in the body. For individuals taking prescription medications, a multivitamin may be harmful because many vitamins and minerals interfere with the effectiveness of certain medications and vice versa. For example, vitamin K interacts with blood clotting medications, such as Coumadin, and can render the medication ineffective if the wrong amount of vitamin K is eaten. Additionally, lifestyle factors may have a negative effect on supplementation. For example, smoking when taking a beta-carotene supplement may increase the risk of lung cancer.
Lastly, and possibly the most important point: The FDA does not regulate supplements, so there tend to be inconsistencies between the supplement and Recommended Daily Allowance (RDA). Supplement manufacturers are not required to create formulas that follow these guidelines. Some multivitamins may give high doses of certain nutrients and low of others, depending on price and availability. Often times, they will use large doses of inexpensive nutrients, possibly in non-bioavailable forms, and make it seem as if it is a potent vitamin. Likewise, nutrients that are expensive or difficult to include in sufficient amounts are omitted or included only in miniscule amounts. Take calcium, for example. Supplements are most commonly in the form of either calcium carbonate, with 40% elemental calcium, or calcium citrate, which has 21% elemental calcium. Supplement manufacturers can use either type and call it a calcium supplement. However, let’s say they add 300 mg of calcium citrate. It may seem as if you’re getting 300mg of calcium, however you’re really only getting 21% of that, which is only 63mg. It’s important to note that the effectiveness of the supplement is not regulated.
The 2010 Dietary Guidelines state that nutrients should come primarily from foods which also contain fiber and other beneficial substances missing from pills. Many vitamins are also better absorbed when eaten throughout the day in small doses, from food, versus consuming it in one sitting. Michael Pollan made the suggestion in his book In Defense of Food that it is possibly not just the isolated nutrient, but the combination of nutrients in a particular food that provides the health benefit. So, multivitamins may be beneficial in normal, healthy individuals if taking a credible supplement under the guidance of a health care provider. However, they can be expensive and may be ineffective for significantly improving health, which is the main purpose of taking supplements in the first place! My recommendation from now on will be just to eat real food and let nature do its job.