Most people take a multivitamin as nutritional insurance, filling gaps that even a reasonably healthy diet can leave behind. National survey data paints a striking picture of how common those gaps are: 94.3% of Americans don’t meet the daily requirement for vitamin D from food alone, 88.5% fall short on vitamin E, and 52.2% on magnesium. A daily multivitamin won’t replace a balanced diet, but for many people it covers the shortfall between what they eat and what their body actually needs.
The Nutrient Gaps in a Typical Diet
You might assume that nutrient deficiencies are a problem for people who eat poorly, but the numbers tell a different story. NHANES data from over 16,000 Americans found widespread inadequacies across multiple vitamins and minerals, even among people who eat a varied diet. The gap is especially large for vitamin D, which is found naturally in very few foods and depends heavily on sun exposure. Vitamin E, concentrated in nuts, seeds, and certain oils, is another nutrient most people simply don’t get enough of from meals alone.
A multivitamin addresses these common shortfalls in a single daily dose. It’s not about megadosing individual nutrients. It’s about bringing your baseline intake closer to recommended levels across the board, particularly for nutrients that are hard to get consistently from food.
Who Benefits Most
While many adults can benefit from a basic multivitamin, certain groups have a stronger nutritional case for one.
People on plant-based diets face specific challenges. Vitamin B12 cannot be obtained naturally without animal foods, so vegans need a supplement or consistently fortified foods. Zinc and iron are present in plant sources like beans, lentils, and whole grains, but they’re absorbed less efficiently from plants than from animal products. A multivitamin formulated for plant-based eaters can help close these gaps without requiring you to track every nutrient individually.
Women who are pregnant or planning to become pregnant have one of the most well-supported reasons to take a multivitamin. Folic acid, a B vitamin included in prenatal formulas, reduces the risk of neural tube defects (serious birth defects of the brain and spine) by more than 70%. The U.S. Preventive Services Task Force specifically recommends that women who are planning or capable of becoming pregnant take 400 to 800 micrograms of folic acid daily. This is one area where the evidence is unambiguous.
Older adults also tend to absorb certain nutrients less efficiently, particularly B12 and vitamin D. People who have had weight-loss surgery, those with digestive conditions that impair absorption, and anyone on a long-term calorie-restricted diet are similarly at higher risk for deficiencies that a multivitamin can help prevent.
What the Evidence Says About Cognition
One of the more compelling recent findings comes from the COSMOS trial, a large, rigorous study that tested daily multivitamin use against a placebo over three years. In the cognitive sub-study (COSMOS-Mind), researchers estimated that taking a daily multivitamin slowed cognitive aging by roughly 60%, equivalent to 1.8 years of preserved brain function over the study period. A separate arm of the trial (COSMOS-Web) found that the multivitamin group showed memory performance equivalent to being 3.1 years younger than the placebo group.
These results don’t mean a multivitamin prevents dementia, and they need to be replicated in larger, longer studies. But for a low-cost, low-risk daily habit, the cognitive signal is notable, particularly for older adults concerned about age-related memory decline.
What Multivitamins Don’t Do
A multivitamin is not a shield against serious chronic disease. A large meta-analysis published in a journal of the American Heart Association found no association between multivitamin use and cardiovascular death, stroke mortality, or stroke incidence. A small initial signal suggesting lower risk of coronary heart disease disappeared when researchers looked only at the most rigorous randomized controlled trials. The USPSTF has concluded there is insufficient evidence that multivitamins prevent cardiovascular disease or cancer in healthy adults.
There are also specific safety considerations. The USPSTF has warned that beta-carotene supplementation, sometimes included in multivitamin formulas, may increase the risk of lung cancer in people who smoke or have smoked, and may raise cardiovascular mortality risk. If you smoke or have a history of smoking, check labels and avoid formulas that include beta-carotene.
The takeaway: a multivitamin works best as a nutritional safety net, not a substitute for diet, exercise, or medical treatment.
How to Get the Most From Your Multivitamin
Timing and food pairing matter more than most people realize. Vitamins A, D, E, and K are fat-soluble, meaning your body absorbs them far more effectively when you take them alongside a meal that contains some fat. Even a small amount works: a handful of nuts, half an avocado, or eggs at breakfast. Taking your multivitamin on an empty stomach can significantly reduce how much of these nutrients your body actually uses.
If your multivitamin contains iron (many formulas designed for women do), be aware that iron can cause mild nausea when taken without food. Taking it with a meal that includes some vitamin C, like fruit or tomatoes, improves iron absorption while reducing stomach discomfort.
Choosing a Quality Product
Dietary supplements in the U.S. aren’t tested for accuracy or purity before they hit store shelves, which means quality varies widely between brands. One reliable signal is the USP Verified Mark. Products carrying this label have been independently tested to confirm they contain the ingredients listed on the label in the declared amounts, don’t contain harmful levels of contaminants like lead or mercury, will actually break down and release into the body within a specified time, and were manufactured under controlled, sanitary conditions that meet FDA standards.
NSF International offers a similar certification program. Either mark gives you reasonable confidence that what’s on the label matches what’s in the tablet. Without third-party verification, you’re relying entirely on the manufacturer’s word.
A Practical Way to Think About It
A multivitamin makes the most sense if you fall into one or more of these categories:
- Your diet has consistent gaps. You eat limited variety, skip meals often, or avoid entire food groups.
- You follow a plant-based diet. B12, zinc, and iron are harder to get and absorb without animal products.
- You’re pregnant or planning to be. Folic acid supplementation has one of the strongest evidence bases in all of nutrition.
- You’re over 50. Nutrient absorption declines with age, and the cognitive data from the COSMOS trial adds another reason to consider it.
- You have a condition affecting absorption. Digestive disorders, prior bariatric surgery, or certain medications can impair how well your body extracts nutrients from food.
For most people, a standard once-daily formula that stays close to 100% of the daily value for each nutrient (rather than megadose formulas offering 500% or more) is the safest and most useful approach. More is not better with fat-soluble vitamins, which can accumulate in the body over time. A well-chosen multivitamin fills the cracks in your diet without pushing any single nutrient into risky territory.