You get vitamins from three main sources: the food you eat, sunlight (for vitamin D), and supplements. For most people, a varied diet built around whole foods covers the majority of vitamin needs without any extra effort. But how your body absorbs, stores, and uses each vitamin varies widely, and understanding those differences helps you make smarter choices about what to eat and whether a supplement is worth it.
Food First: The Most Reliable Source
Whole foods remain the best way to get your vitamins because they deliver nutrients in combinations that help your body absorb them. A serving of spinach, for instance, gives you folate, vitamin K, and vitamin A precursors alongside fiber and minerals that work together during digestion. Supplements isolate single nutrients, which can be useful in specific situations but can’t replicate the full package food provides.
The practical strategy is simple: eat a wide variety of colorful fruits and vegetables, whole grains, lean proteins, dairy or fortified alternatives, nuts, and seeds. No single food covers everything. Organ meats and eggs are dense in B12 and fat-soluble vitamins. Citrus fruits and bell peppers are loaded with vitamin C. Fatty fish like salmon and mackerel deliver vitamin D and omega-3s. Fermented foods like cheese, yogurt, and natto provide vitamin K2. The more diverse your plate, the fewer gaps you’ll have.
How Your Body Absorbs Different Vitamins
Vitamins fall into two categories, and the distinction matters for how you eat them. Water-soluble vitamins (the B vitamins and vitamin C) dissolve in water and pass directly into your bloodstream during digestion. Your body doesn’t store them in meaningful amounts. Whatever you don’t use gets flushed out through urine, so you need a steady daily intake.
Fat-soluble vitamins (A, D, E, and K) work differently. They dissolve in fat and require bile acids and dietary fat for your body to absorb them properly. These vitamins get stored in your fatty tissues and liver, which means your body can draw on reserves during periods when your intake drops. It also means they can accumulate to harmful levels if you take too much over time.
The practical takeaway: when you eat foods rich in fat-soluble vitamins, pair them with some fat. A salad with olive oil dressing helps you absorb the vitamin K from leafy greens and the vitamin A precursors from carrots far better than eating those vegetables dry. Cooking vegetables in a small amount of oil works the same way. For water-soluble vitamins, consistency matters more than pairing. Eating fruits and vegetables daily keeps levels topped up since your body won’t hold onto yesterday’s surplus.
Getting Vitamin D From Sunlight
Vitamin D is unique because your skin manufactures it when exposed to ultraviolet B (UVB) rays from the sun. Exposing your bare arms and legs to midday sun (between 10 a.m. and 3 p.m.) for 5 to 30 minutes, twice a week, can be enough to meet your needs. But several factors shift that window considerably.
Skin pigmentation plays a major role. People with darker skin may need up to ten times longer in the sun to produce the same amount of vitamin D as someone with fair skin. Geography matters too. If you live at or above 40 degrees north latitude (roughly the line running through Boston, Madrid, or Beijing), UVB radiation is too weak for your skin to make vitamin D from November through early March. Move ten degrees farther north, to cities like Edmonton, and that “vitamin D winter” stretches from October to April.
During those months, or if you spend most of your time indoors, dietary sources and supplements become your primary options. Fatty fish, fortified milk, fortified cereals, and egg yolks all provide vitamin D, though it’s difficult to get enough from food alone if sun exposure is limited. This is one vitamin where supplementation often fills a genuine gap.
Vitamins Your Gut Bacteria Make
Your intestinal bacteria produce certain vitamins on their own, particularly vitamin K2. Different bacterial species in your gut synthesize different forms of this vitamin. However, research shows that the bioavailability of bacterially produced K2 is generally poor because most of it stays bound to bacterial membranes inside the gut rather than being absorbed into your bloodstream. Studies have confirmed that when dietary vitamin K intake drops, gut bacteria don’t compensate for the shortfall.
The bottom line is that while your microbiome contributes to vitamin K2 production, you can’t rely on it as your main source. Diet remains the principal way to get functionally available K2. Foods like hard cheeses, egg yolks, butter, and especially natto (a fermented soybean product) are the most practical sources.
When Supplements Make Sense
Most healthy adults eating a varied diet don’t need a daily multivitamin. But certain life stages and dietary patterns create gaps that food alone may not fill.
- Pregnancy: Folic acid supplementation before and during early pregnancy reduces the risk of neural tube defects. A standard prenatal vitamin covers this along with iron and other key nutrients. Taking additional supplements beyond a prenatal formula during pregnancy requires caution, since many have not been well tested for safety in pregnant or nursing women.
- Vegan and vegetarian diets: Vitamin B12 occurs naturally only in animal products. If you eat no meat, eggs, or dairy, you need a B12 supplement or reliable fortified foods. Vegans may also fall short on vitamin D, omega-3 fatty acids, and iron depending on their food choices.
- Older adults: The ability to absorb B12 from food declines with age, making supplementation or fortified foods important after 50. Vitamin D needs also increase because skin becomes less efficient at synthesis and time spent outdoors often drops. A specific combination of vitamins C and E, zinc, copper, lutein, and zeaxanthin (known as the AREDS formula) has been shown to slow vision loss in people with age-related macular degeneration.
- Limited sun exposure: If you live in a northern climate, work indoors, or have darker skin, a vitamin D supplement of 1,000 to 2,000 IU daily through the winter months is a common recommendation.
Avoiding Too Much of a Good Thing
Because fat-soluble vitamins accumulate in your body, it’s possible to overdose on them through high-dose supplements in a way that’s nearly impossible through food alone. Vitamin A toxicity can cause liver damage, nausea, and in severe cases, increased pressure in the skull. Excess vitamin D leads to dangerously high calcium levels. Even water-soluble vitamins aren’t risk-free at extreme doses. The European Food Safety Authority sets the upper tolerable intake for vitamin B6 at 25 milligrams per day, including for pregnant and lactating women. Exceeding that over time can cause nerve damage in the hands and feet.
The pattern is consistent: food sources almost never push you past safe limits, while supplements easily can. If you do supplement, stick to doses at or near the recommended daily value unless a healthcare provider has identified a specific deficiency.
Choosing a Quality Supplement
Dietary supplements in many countries aren’t required to prove their contents match their labels before going to market. Third-party certification helps close that gap. An independent organization tests the product to verify that what’s on the label is actually in the bottle and that the product is free from contaminants.
Four widely recognized seals to look for are USP Verified, NSF Certified Sport, Informed Sport, and BSCG Certified Drug Free. These certifications confirm that the product’s contents match the label and that manufacturing standards were followed. They do not, however, evaluate whether the supplement is effective or safe for your particular situation. They simply confirm you’re getting what you paid for, at the dose listed, without harmful extras.
Testing Your Vitamin Levels
If you suspect a deficiency, a blood test is the most direct way to confirm it. Vitamin B12 and folate are commonly checked when symptoms like unusual fatigue, weakness, numbness, or a specific type of anemia appear. Vitamin D levels are measured through a simple blood draw and are routinely ordered when someone reports bone pain, frequent illness, or has known risk factors for deficiency.
Interpreting results isn’t always straightforward. Inflammation in the body and certain medications can skew vitamin B levels, and different labs use slightly different reference ranges for what counts as “normal.” A single low reading doesn’t always mean you’re deficient, and a normal reading doesn’t always mean your levels are optimal. Your results are most useful when combined with your symptoms, diet history, and overall health picture rather than read in isolation.