For most people eating a reasonably varied diet, a daily multivitamin isn’t necessary. But that doesn’t mean vitamins don’t matter. Your body absolutely requires 13 essential vitamins to function, and certain groups of people genuinely struggle to get enough from food alone. The real answer depends on who you are, what you eat, and what stage of life you’re in.
What Vitamins Actually Do in Your Body
Vitamins aren’t optional extras. They’re involved in nearly every process that keeps you alive. Vitamin D helps your body absorb calcium for bone strength. Vitamin C is essential for wound healing and iron absorption. The B vitamins help convert food into energy, form red blood cells, and maintain your nervous system. Vitamin K is the reason your blood clots when you get a cut. Vitamin A maintains your vision, skin, and immune defenses. Without adequate levels of any one of these, specific systems start to break down.
The 13 essential vitamins fall into two categories. Fat-soluble vitamins (A, D, E, and K) are stored in your body’s fat tissue and liver, so they build up over time. Water-soluble vitamins (C and the eight B vitamins) aren’t stored as efficiently. Your body uses what it needs and flushes the rest, which means you need a more consistent daily supply of them.
Most People Fall Short on Several Nutrients
Global dietary data paints a starker picture than many people expect. A 2024 modeling analysis published in The Lancet Global Health estimated that more than 5 billion people worldwide don’t consume enough iodine, vitamin E, or calcium from food alone. Over 4 billion fall short on iron, riboflavin, folate, and vitamin C. These numbers reflect intake from food without fortification or supplements, but they show how common nutritional gaps are even before you account for individual eating habits.
Women consistently have higher rates of inadequate intake than men for several nutrients, including iron, vitamin B12, calcium, folate, and selenium. Men tend to fall shorter on magnesium, vitamin B6, zinc, and vitamin C. Age matters too. Older adults absorb less B12 from food as stomach acid production declines, and they synthesize less vitamin D from sunlight.
Who Actually Needs Supplements
Some people can’t realistically meet their vitamin needs through food, no matter how well they eat. If you follow a vegan or strict vegetarian diet, vitamin B12 is your most critical gap. B12 occurs naturally only in animal products. Studies have found that roughly 52% of vegans have deficient B12 levels, compared to about 1% of omnivores. A European study comparing the groups found even higher rates: 92% of vegans and 77% of lacto-ovo vegetarians were B12 deficient, versus 11% of meat eaters. Your liver can store enough B12 to last a few years, so deficiency doesn’t show up immediately, but when it does, it can cause nerve damage, fatigue, and cognitive problems.
Pregnant women need more folate to support DNA production and fetal development, making a prenatal vitamin genuinely important. Infants born to vegan mothers who don’t supplement can show signs of B12 deficiency as early as four to seven months of age.
People with age-related macular degeneration may benefit from a specific combination of vitamins C and E, zinc, copper, lutein, and zeaxanthin, which research suggests can slow further vision loss. And anyone living in northern latitudes or spending most of their time indoors often needs supplemental vitamin D, since dietary sources alone rarely provide enough.
Multivitamins and Chronic Disease Prevention
If you’re taking a multivitamin hoping to prevent cancer or heart disease, the evidence is disappointing. The U.S. Preventive Services Task Force reviewed nine randomized controlled trials on multivitamin use and found inadequate evidence that supplementation prevents cardiovascular disease or cancer. That doesn’t mean vitamins are useless. It means that for people who aren’t deficient, adding a pill on top of adequate nutrition doesn’t appear to offer extra protection against major diseases.
The benefit of supplementation is correcting a shortfall, not supercharging a system that’s already working. If your diet provides enough vitamin C, taking 500 mg more won’t make your immune system stronger. Your body will simply excrete the excess.
Supplements Can Be as Absorbable as Food
There’s a common belief that vitamins from food are always better absorbed than those from supplements. The reality is more nuanced. Vitamins and minerals added to foods or taken as supplements are generally at least as bioavailable as those naturally present in food, and often more so. Certain supplemental forms are actually absorbed better than their food-bound counterparts. Methylfolate, for instance, is more bioavailable than the folic acid used in many fortified foods.
Plant-based foods can have lower bioavailability for some minerals because compounds like phytate and fiber bind to nutrients and reduce absorption. That said, whole foods deliver vitamins alongside fiber, antioxidants, and other compounds that work together in ways a pill can’t replicate. Supplements fill gaps. They don’t replace the full package that food provides.
Too Much Can Be Harmful
Fat-soluble vitamins accumulate in your body, and taking high doses over time can cause real damage. Chronic excess vitamin A leads to headaches, nausea, blurred vision, hair loss, dry skin, and in severe cases, liver disease. One documented case involved a patient who took high-dose vitamin A averaging 120 mg per day for eight years and developed liver disease that was initially unexplained.
Vitamin D toxicity causes calcium to build up in your kidneys, potentially leading to irreversible kidney damage, nausea, muscle weakness, and in extreme cases, coma. Vitamin E at doses above 400 IU daily has been linked to a higher risk of death from all causes. Even vitamin K, which rarely causes problems in adults, can trigger hemolytic anemia in infants and adolescents at excessive doses.
Water-soluble vitamins are safer in high amounts since your body excretes the surplus, but they’re not entirely risk-free either. The key point: more is not better, and mega-dosing without a diagnosed deficiency introduces risk with no proven upside.
How to Take Vitamins for Best Absorption
If you do take supplements, timing and pairing them with food makes a difference. Fat-soluble vitamins (A, D, E, and K) need dietary fat to be absorbed properly. Take them with a meal that includes some fat, even just a handful of nuts or avocado on toast.
Water-soluble vitamins like C and the B vitamins absorb best on an empty stomach with water. That creates a practical conflict with multivitamins, which contain both types. The best approach for a multivitamin is to take it with a meal, since the fat-soluble components need fat and your stomach produces acids during digestion that aid absorption overall. Taking a multivitamin on an empty stomach means the fat-soluble vitamins largely pass through without being absorbed.
Prenatal vitamins should also be taken with a meal. If you take calcium separately, calcium citrate can be taken with or without food, while calcium carbonate needs stomach acid, so it absorbs better during a meal.
The Practical Bottom Line
Vitamins are essential. Vitamin supplements are situational. If you eat a varied diet with fruits, vegetables, whole grains, and some animal products or fortified foods, you’re likely covering most of your needs. If you’re vegan, pregnant, over 65, rarely get sun exposure, or have a condition that limits nutrient absorption, targeted supplementation fills gaps that food alone can’t. A standard multivitamin is a reasonable insurance policy for people with inconsistent diets, but it’s not a substitute for eating well, and taking high doses without a specific reason adds risk without clear reward.