Millions of people purchase dietary supplements, hoping to improve their health, correct nutritional shortfalls, or even prevent chronic diseases.
You might ask your doctor, “What supplements should I take?” If you’re interested in or already taking a supplement, what you should be asking is why you’re taking it and whether you truly need it, a Cleveland Clinic expert recommends.
“I get questions all the time about supplements, and I also have patients who are taking a lot of supplements,” says Cleveland Clinic dietitian Julia Zumpano, RDN, LD. “We spend a good amount of time going through all the supplements they’re on and why they’re on them. I feel it is important to educate them on the safe and effective use of supplements and helping them decide whether or not they need them. It’s a hot topic, for sure.”
Do You Really Need Supplements?
Zumpano recommends obtaining nutrients from dietary sources as much as possible rather than from supplements. By choosing the right foods, you’ll gain a bounty of nutrients that work synergistically in your body to promote health, whereas an isolated nutrient in pill form may not offer the same benefit.
That doesn’t mean taking supplements is bad—sometimes, it might be a necessary nutrient shortcut. So, who needs supplements?
Some older adults and people with digestive disorders may have difficulty absorbing sufficient nutrients and may require a supplement. People engaged in more intensive exercise training or individuals recovering from illness or surgery may require nutrients in quantities that only supplements can provide.
Some people fail to consume enough nutritious foods due to factors like poor dental health and swallowing or chewing difficulties. Others have busy schedules that prevent them from eating a balanced diet.
“If you’re eating all food groups and you’re focused on balanced meals and healthy choices, you should be able to meet your day-to-day needs,” Zumpano says. “But do Americans eat a balanced diet and are Americans meeting all their nutrient needs? Most likely not.”
Common Supplements: What the Evidence Says
Here’s a look at some commonly used dietary supplements and what you should know about them.
Multivitamins
Most multivitamins contain the recommended dietary allowance (RDA) of essential vitamins and minerals—vitamins A, B-complex vitamins, C, D, E and K, as well as minerals like calcium, magnesium, iron, and zinc. Some products marketed specifically for men include ingredients like added zinc for immune health or selenium to support prostate health, whereas multivitamins for women may contain more calcium, iron, and folic acid.
Overall, studies of multivitamins’ effects on chronic disease prevention have produced conflicting results. The Physicians’ Health Study II, which involved 14,641 male health professionals, ages 50 and older, found that use of a daily multivitamin for an average of more than 11 years was associated with a slight reduction in overall cancer risk but offered no protection against cardiovascular disease. Similarly, the COSMOS study found no benefit from two years of daily multivitamin use in terms of preventing cancer or cardiovascular disease. However, a subsequent analysis of the COSMOS data found that taking the multivitamin was linked to a modest slowing of biological aging (Nature Medicine, March 9, 2026), and three sub-studies of COSMOS trial participants suggested that multivitamin use may help improve cognition.
Vitamin D
This vitamin plays a key role in bone health and muscle and immune function. Vitamin D shortfalls are common, partly because dietary sources of vitamin D are limited. Furthermore, while most people can obtain the vitamin D they need by getting 10 to 15 minutes of sun exposure (without sunscreen) three times a week, concerns about skin cancer may prevent others from meeting this goal.
The RDA for vitamin D—600 to 800 international units (IU) a day—is widely considered to be too low, so some experts recommend taking 1,000 to 2,000 IU of supplemental vitamin D (preferably D3) daily. Taking it with your largest meal can help improve absorption. A large study found that daily vitamin D supplementation (2,000 IU) did not significantly reduce the risk of heart disease and cancer. However, a more recent study, TARGET-D, found that among 630 adults (average age 63) with heart disease, nearly four years of taking carefully personalized doses based on serial blood testing to achieve blood vitamin D levels of 40 to 80 nanograms per milliliter was associated with a significantly reduced risk of heart attack. Slightly more than half of the participants required more than 5,000 IU of vitamin D each day to achieve these blood levels.
“The TARGET-D trial revealed that adults with established heart disease using a treat-to-target approach cut the risk of heart attack in half, but that has to do with testing levels and treating based on the value,” Zumpano says. “I think that’s key.”
Calcium
Men ages 70 and younger and women ages 50 and younger should get at least 1,000 milligrams (mg) of calcium a day, while men ages 71 and older and women ages 51 and older should aim for 1,200 mg daily.
Zumpano recommends getting calcium from foods (e.g., milk, yogurt) because some studies have linked calcium supplements with an increased risk of cardiovascular events (although other studies have found no such risk): “If you’re not eating dairy, we would recommend a calcium supplement, but I recommend foods first because of this question hovering around calcium supplements.”
If you need a supplement, limit the calcium dose to no more than 500 to 600 mg at a time to maximize your absorption. Note that calcium carbonate provides more elemental calcium (40%) versus calcium citrate (24%), so you’ll need to take more calcium citrate to gain the same amount you would get from calcium carbonate products. Calcium carbonate requires stomach acid for proper absorption; take it with food to maximize absorption.
Vitamin B12
Research has linked vitamin B12 deficiency with cognitive dysfunction, and B12 shortfalls may cause fatigue, muscle weakness, and other neurological symptoms. Older adults, vegetarians, and people with stomach and intestinal disorders face a greater risk of B12 deficiency.
If you can’t get the RDA of vitamin B12 (2.4 micrograms) from fish, fortified cereals, milk, and beef and organ meats, your healthcare provider may recommend supplements. For most people, taking supplemental vitamin B12 is safe (the vitamin is water-soluble, so any amounts you don’t need are excreted in urine). However, “B12 supplements can interfere with certain medications if you take too much,” Zumpano says. “It’s less risky because it’s water-soluble, but that doesn’t mean it has no risk at all.”
Fish oil
Diets rich in the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can have some beneficial effects on brain health and have been shown to lower triglycerides and modestly reduce blood pressure. However, the evidence that omega-3 fish oil supplements can prevent major cardiovascular events is inconclusive. So, the American Heart Association recommends eating at least two 3-ounce servings of fatty fish (e.g., mackerel, herring, tuna, trout) each week. Also, eat flaxseed, chia seeds, walnuts, and soybeans regularly. These plant foods are rich in alpha-linolenic acid, which your body can convert in small amounts to EPA and DHA.
Fish oil supplements can increase the risk of bleeding, especially if you take blood-thinning medications. Moreover, research has linked omega-3 supplements (especially higher doses) with an increased risk of atrial fibrillation, a common irregular heart rhythm and a major stroke risk factor. “In our clinic, we have decreased how frequently we recommend fish oil,” Zumpano says. “If you have a risk for an arrhythmia, we usually recommend not taking a fish oil supplement.”
Iron
Iron supplements may be necessary if you eat a plant-based diet, but Zumpano does not recommend taking them unless you need to correct a deficiency identified on blood testing. You can get sufficient iron from foods such as lean meats, seafood, spinach, beans, and lentils. The RDA for iron is 8 mg a day for men ages 19 to 50 and all adults ages 51 and older, and 18 mg a day for women ages 19 to 50. Be aware that taking too much iron can cause gastrointestinal side effects such as upset stomach, constipation, diarrhea, nausea, and abdominal pain.
Magnesium
Found in dietary sources like pumpkin and chia seeds, almonds, and spinach, this mineral plays a vital role in many physiological processes in your body. The RDA for magnesium is 420 mg a day for men and 320 mg daily for women. Low magnesium levels are more common in older adults, individuals with Type 2 diabetes, and those with poor diets or malabsorption issues in the gut.
One of the most popular magnesium supplements, magnesium glycinate, can help with sleep, migraines, anxiety, muscle tension, and restless legs syndrome. Another popular form, magnesium citrate, is well known for its laxative effects, and it also may relieve migraines and help with muscle soreness.
Fiber
Fiber in foods like whole grains, berries, and other fruits, beans, peas, and lentils can help to remove cholesterol from the body, lower blood sugar, and improve digestion. Plus, these foods are nutrient-dense, so Zumpano recommends prioritizing them to meet your daily fiber needs. However, since the average American diet provides only about 13 grams of fiber per day (below recommended levels), fiber supplements like psyllium can help cover any shortfalls. Choose a supplement that is minimally processed, with no artificial colors/dyes or added sweeteners, Zumpano advises. But getting enough fiber from whole foods is best because fiber-rich foods are nutrient-rich and provide additional benefits, whereas a supplement does not.
Probiotics
These supplements contain beneficial bacteria that some data suggest can boost immune function, reduce inflammation, and possibly improve cholesterol levels. Depending on the strain of bacteria used, probiotic supplements may provide some relief for individuals with digestive disorders like irritable bowel syndrome, ulcerative colitis, acute infectious diarrhea, and diarrhea associated with antibiotic use. “I don’t suggest them in a supplement form often, but I do encourage dietary sources such as yogurt, kefir, sauerkraut, kimchi, fermented foods, and miso,” Zumpano says. “Post-antibiotic use, I may recommend a broad-spectrum probiotic. If someone has traveler’s diarrhea or constipation, there are different strains that can help with those, so that’s where I might recommend a specific probiotic strain.”
How to Choose Safe, Effective Supplements
If you decide to use a dietary supplement, it’s best to purchase it from a large national manufacturer that’s invested in maintaining a good reputation. Carefully review the labels of any products you purchase, and note the nutrient content, RDA, the percent daily value, and the number of pills per serving.
Also, supplements do not face the same regulatory oversight and standardized quality controls as prescription pharmaceuticals, so look for labels bearing the symbols of independent organizations that test supplements for their quality, purity, and content. Among those organizations:
A simple tip for how to choose supplements is to avoid products that make exaggerated or misleading health claims—if it sounds too good to be true, it probably is.
Interactions and Risks of Dietary Supplements
When it comes to dietary supplement safety, understand that along with the benefits they can offer, supplements can be associated with certain risks and side effects, especially if you take them in excess—for example, the bleeding and arrhythmia risks associated with fish oil supplements, and the gastrointestinal side effects of excessive iron supplementation.
Moreover, beware of potential supplement and medication interactions. For instance, high doses of fish oil and vitamin E supplements (among others) have some blood-thinning properties, and they can potentially augment the anticoagulant effects of drugs like warfarin (Coumadin) and increase the risk of bleeding.
Practical Tips for Supplement Use
So, in lieu of the potential for side effects and medication interactions, keep a record of the supplements and medications you take, and talk to your healthcare provider about your supplement use. Ask yourself and/or your healthcare provider these questions about any dietary supplement you’re taking or considering:
- Why are you taking it?
- Do you really need it?
- Have you been tested and confirmed to have a deficiency in that particular nutrient?
- Can it interact with any medications you take?
- Are you taking the proper dosage?
- Are you taking it properly—with or without food?
- Has the supplement undergone third-party testing?
Importantly, be sure you understand what a dietary supplement can and cannot do for you, Zumpano advises.
“We know that a supplement can’t prevent a chronic disease, but it can help you feel better, prevent or correct a deficiency, and help your body work more efficiently,” she adds. “Just educate yourself and ask a lot of questions. It’s important to understand why you’re taking it.”
