“VITAMINS” MAKE UP a massive category, but, in general, it helps to think of them as tiny general contractors that build and repair various things on and inside your body.

Your body needs small amounts of vitamins to function properly, says Mariana Dineen, a registered dietitian and founder of the virtual nutrition practice Elemento Health. Vitamins help fortify your immune system, build your muscles and bones, and much more.

“They are essential nutrients, meaning that our bodies can’t produce enough of them, so we need to get them through our diet,” she says. Vitamin-packed foods like fruits, vegetables, whole grains, and high-quality meats can help you get enough. In some cases, vitamin supplements are helpful, too.

Are Vitamins Different Than Supplements?

YES. ON A biological level, vitamins are organic compounds. Your body needs vitamins A, C, D, E, K, and the eight B vitamins: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9) and cyanocobalamin (B12).

These nutrients occur naturally in a wide variety of foods, like fruits and vegetables (A, C, and K), nuts (E), meat (B), and mushrooms (D). Your body also makes vitamin D from sunlight, and your gut bacteria make some vitamin K.

By comparison, vitamin supplements contain vitamins in a capsule, tablet, liquid, gummy, or powder form. (Or at least that’s the idea. More on that soon.)

Multivitamins, which some people use interchangeably with vitamins, contain a mix of vitamins, although many vitamin supplements also contain other substances, like minerals, herbs and botanicals, protein, fatty acids, or probiotics.

Are Vitamins Healthy?

YES, IN THE right amounts. If you don’t consume enough of certain vitamins, you can get seriously sick. Vitamin deficiencies can cause a wide range of health problems, like night blindness (vitamin A deficiency), fatigue (vitamin B deficiencies), swollen gums (vitamin C deficiency), weak bones (vitamin D deficiency), muscle problems (vitamin E deficiency), or excess bleeding (vitamin K deficiency).

Vitamins can become unhealthy if you take too much, which is more likely with supplements than food. Vitamin C and B vitamins are water soluble, so we pee out what we don’t need in a matter of days. Vitamins A, D, E, and K are fat soluble, so we can store extra in our tissues. It’s easier to overdo the fat-soluble vitamins because they build up in your fat stores. They can accumulate in your body to toxic levels, causing harmful side effects. It’s harder, but possible, to consume too much vitamin C and B vitamins.

“Supplements are meant to supplement an already balanced diet,” says Dezi Abeyta, RDN, a Men’s Health nutrition adviser and founder of Foodtalk Nutrition LLC. “I think most guys get it the other way around, where they’re thinking about supplementation versus thinking about how to create a foundation and making sure that their foods are nutrient dense, so that they contain the water-soluble and fat-soluble vitamins that your body needs.”

Foods also give you an array of helpful nutrients beyond vitamins.

“Vitamin supplements are not going to be able to provide that whole package that whole foods are going to give you: the fibers, the vitamins, the minerals, the antioxidants, this synergy that vitamin supplements are not able to provide,” says Dineen.

Are Vitamins Safe?

THEY CAN BE, but don’t just grab the first one you see and assume it’s fine. Vitamin supplements are not regulated by the Food and Drug Administration, so the onus is on companies to make the supplements safely. Do your homework and select a product verified by a third party like NSF.

“It is important to select supplements from brands with third-party testing or certifications to ensure purity, to ensure dosage accuracy, and even the absence of other harmful additives,” says Dineen.

If you take vitamin supplements, stick to the recommended dose. Every vitamin has a tolerable upper intake limit—the maximum dose you can consume safely. It’s easy to exceed the max if you take more than one supplement or eat foods and beverages with extra vitamins added, like energy drinks, which often contain high doses of B vitamins.

“Many vitamins and fortified foods contain some of the same ingredients, so using multiple products with overlapping ingredients can lead to unintentional overdosing,” says Dineen.

Make sure your healthcare provider knows that you’re taking vitamin supplements as well.

“Seeking professional advice, whether it’s from your registered dietitian or doctor is important, because it will ensure that the vitamin intake aligns with your personal needs, and that it’s going to avoid interactions with medications or other vitamins or other nutrients,” says Dineen.

Who Should Take Vitamins?

NOT EVERYONE NEEDS to take vitamin supplements. A recent study from the National Institutes of Health showed that on average, multivitamins didn’t protect people from an early death (they didn’t increase risk either).

However, vitamin supplements can be helpful if you are falling short of your nutritional requirements.

“They can be very healthy, and they can be essential for our wellbeing, but only if they are in the right amount and when used appropriately,” says Dineen. “They can be beneficial if they are used to fill a nutritional gap.”

Talk to your healthcare provider about a vitamin supplement if you have the following:

• Symptoms of a deficiency. A healthcare provider can order blood testing to reveal vitamin deficiencies. They can then recommend a supplement to help you boost your levels if needed.
• A limited diet. Vitamin supplements can help people with limited diets, such as vegetarian or vegan diets, get enough vitamins like B12.
• Gut problems. Sometimes people with digestive disorders that affect nutrient absorption, like Celiac disease, benefit from vitamin supplements, says Dineen.