What Are Some Examples of Dietary Supplements?

Dietary supplements span a surprisingly wide range of products, from the familiar multivitamin tablet to herbal extracts, fish oil capsules, protein powders, and newer compounds marketed for aging. In the United States alone, the category legally includes vitamins, minerals, herbs, amino acids, enzymes, and various concentrates or extracts intended to supplement the diet. The definition was broadened in 1994 by federal legislation, and the boundary between supplements and drugs has been blurry ever since. What follows is a practical walk through the major categories, what each type is actually used for, and what the research says about the most popular examples.

What Counts as a Dietary Supplement

The 1994 Dietary Supplement Health and Education Act (DSHEA) expanded the legal definition of a dietary supplement and loosened restrictions on the health claims manufacturers could put on labels.¹ Unlike prescription drugs or even food additives, supplements do not need premarket approval from the FDA. Instead, the FDA monitors them after they hit shelves, and if a product turns out to be harmful, the agency bears the burden of proving it unsafe before pulling it.² This framework means the supplement aisle is essentially self-policing at the point of sale, which has real consequences for quality and safety that show up later in the article.

Vitamins

Vitamins are the most recognizable category. They include both water-soluble types (the B-complex family, vitamin C) and fat-soluble ones (A, D, E, K). Fat-soluble vitamins are stored in body tissue rather than flushed out quickly, which is why overdoing them can cause trouble: excess vitamin A can lead to headaches, blurred vision, and even bone-density loss; too much vitamin D can cause joint pain and kidney problems; and high-dose vitamin E has been linked to increased bleeding risk.³ Water-soluble vitamins are generally safer in excess because the body excretes what it doesn’t need, though that doesn’t mean mega-dosing is beneficial.

Vitamin D and Calcium

Vitamin D is one of the most widely supplemented nutrients, often paired with calcium for bone health. Research consistently shows that the pairing matters: calcium with vitamin D supplementation improves bone mineral density, but vitamin D alone does not appear to have the same effect.⁴ A trial in adults 65 and older found that the calcium-plus-D group gained bone density at the hip, spine, and total body compared to placebo, and had fewer nonvertebral fractures over three years.⁵ The takeaway is practical: if you’re supplementing for bone health, vitamin D by itself is probably not enough.

Vitamin B12

B12 is essential for nerve function and red blood cell production, and most people eating animal products get plenty from food. But two groups are at elevated risk of deficiency: older adults (whose ability to absorb B12 from food declines with age) and people eating plant-based diets, since B12 is found almost exclusively in animal-derived foods.⁶ Estimates of B12 deficiency in older populations range widely, from about 2% to 35% depending on the age group and region studied.⁷ The deficiency often develops without obvious symptoms, but if it progresses, it can contribute to cardiovascular problems and neurological damage. Supplementation or adequate intake through fortified foods and dairy can prevent that progression.⁸

Essential Minerals

Mineral supplements fill gaps that diet sometimes leaves open. Iron, magnesium, calcium, and zinc are the ones most commonly sold on their own or in combination formulas.

Iron

Iron supplements, usually in the form of ferrous sulfate, are a standard treatment for iron-deficiency anemia. They work, but they’re notorious for digestive side effects. A meta-analysis of randomized trials found that ferrous sulfate roughly doubled the odds of gastrointestinal complaints compared to placebo, and roughly tripled the odds compared to intravenous iron.⁹ Nausea, constipation, and stomach pain are common enough that many people abandon iron supplements before their deficiency resolves. Alternative forms of iron (ferrous gluconate, iron bisglycinate) and lower-dose strategies are sometimes used to reduce these effects, though the evidence on which formulation is gentlest is still debated.

Magnesium

Magnesium plays a role in hundreds of enzymatic reactions, including muscle contraction, nerve signaling, and blood-pressure regulation. Experimental and clinical evidence shows that magnesium deficiency contributes to elevated blood pressure, while supplementation produces modest but consistent blood-pressure-lowering effects.¹⁰ Magnesium supplements come in many forms: magnesium citrate, oxide, glycinate, threonate, and others. The differences are mainly about how well each is absorbed and which side effects it tends to cause. Magnesium oxide, for instance, is cheap but poorly absorbed, and high doses act as a laxative. Magnesium glycinate tends to be gentler on the stomach.

Fish Oil and Omega-3 Fatty Acids

Fish oil capsules are one of the best-selling supplement categories worldwide. They supply omega-3 fatty acids, primarily EPA and DHA, which have anti-inflammatory, blood-lipid-lowering, and blood-thinning properties. Lab and clinical research suggest that fish oil supplementation may reduce the risk of cardiovascular events, and it shows potential benefits for people with hypertension, coronary heart disease, arrhythmias, or heart failure.¹¹ The picture isn’t clean, though. Several large trials in patients with existing coronary artery disease or prior heart attacks failed to show a meaningful benefit on major cardiovascular endpoints, raising questions about whether the earlier optimism was warranted.¹² The honest summary is that fish oil probably helps some people with specific cardiovascular risk profiles, but it’s not the universal heart protectant it was once marketed as.

Herbal and Botanical Supplements

This is where the supplement world gets especially diverse. Herbal products include everything from traditional remedies like turmeric and ashwagandha to extracts with documented drug interactions like St. John’s wort. The evidence ranges from reasonably solid to barely there, depending on the plant.

St. John’s Wort

St. John’s wort is probably the most-studied herbal supplement for mood. Clinical evidence shows it is more effective than placebo and roughly as effective as older tricyclic antidepressants for mild-to-moderate depression.¹³ But the reason it deserves its own section isn’t efficacy, it’s drug interactions. St. John’s wort affects the liver enzymes responsible for breaking down many medications, including antidepressants like SSRIs.¹⁴ Lab testing has confirmed that the extract’s constituents can potently inhibit several cytochrome P450 enzymes that metabolize a wide range of drugs.¹⁵ That means it can change how your body processes everything from birth control pills to blood thinners to organ-transplant drugs. If you’re on any prescription medication and considering St. John’s wort, a conversation with a pharmacist isn’t optional.

Turmeric and Curcumin

Curcumin, the active compound in turmeric, has become a mainstream supplement for joint pain and inflammation. Clinical trials in people with osteoarthritis have found that curcumin improves pain, physical function, and quality of life, with patients also reporting they use fewer conventional painkillers while taking it.¹⁶ Animal studies and clinical evidence consistently show anti-inflammatory and analgesic effects, and the side-effect profile appears to be milder than many conventional painkillers.¹⁷ The catch is bioavailability: curcumin on its own is poorly absorbed. Most supplements now include piperine (from black pepper) or use special formulations to improve uptake. Whether those enhanced versions deliver enough curcumin to match what was used in trials is hard to verify from a label.

Ashwagandha

Ashwagandha (Withania somnifera) has moved from Ayurvedic tradition into the mainstream as a stress-relief supplement. A meta-analysis found that ashwagandha supplementation significantly reduced perceived stress scores and lowered cortisol levels after about eight weeks of treatment.¹⁸ Individual trials back this up: one placebo-controlled study found a roughly 23% drop in cortisol in the ashwagandha group over time, compared to essentially no change in placebo.¹⁹ Another randomized trial showed greater reductions in morning cortisol alongside increases in serotonin compared to placebo.²⁰ The effects are real but moderate. Ashwagandha isn’t a replacement for therapy or medication in someone with clinical anxiety, but for everyday stress it has more research support than most adaptogens.

Sports and Performance Supplements

Protein powders and creatine sit at the performance end of the supplement spectrum. They’re aimed at people who exercise regularly and want to recover faster or build more muscle.

Whey Protein

Whey protein is the most popular protein supplement, derived from dairy during cheese production. A double-blind placebo-controlled study found that participants supplementing with whey protein around their workouts saw greater increases in muscle circumference, strength, and exercise volume compared to placebo, even when their total protein intake from food was lower.²¹ The researchers noted that the timing and composition of protein intake seemed to matter more than the total amount. That’s consistent with broader sports nutrition evidence: getting protein close to a training session appears to give a slight edge for muscle building, though the effect is modest and most people eating a protein-rich diet won’t notice a dramatic difference from adding a shake.

Creatine

Creatine monohydrate is one of the most extensively researched performance supplements. It works by increasing the body’s stores of phosphocreatine, which helps regenerate the energy molecule ATP during short, high-intensity efforts like sprinting or heavy lifting. Beyond muscle performance, creatine has attracted interest for cognitive effects: a systematic review of randomized trials examined its impact on mental tasks in healthy people.²² The evidence for cognitive benefits is still in its early stages, but the direction of findings has been encouraging enough to sustain ongoing research. For its primary use in strength and power sports, creatine monohydrate has an unusually strong evidence base and an excellent safety profile at standard doses.

Collagen

Collagen supplements, usually sold as hydrolyzed collagen peptides, are marketed for skin health and joint support. The research here is more promising than many skeptics expect. A review of the literature found that hydrolyzed collagen supplementation was associated with decreased wrinkle formation, increased skin elasticity and hydration, and higher collagen density in the skin. On the orthopedic side, the same review reported improvements in bone strength, joint stiffness and mobility, and reduced pain.²³ The mechanism isn’t fully understood — your body breaks ingested collagen into amino acids and peptides, and it’s debated how much of that raw material ends up being reassembled into collagen in your skin or joints versus being used for other purposes. Still, the clinical signal is consistent enough across multiple trials to suggest something real is happening.

Melatonin

Melatonin is technically a hormone, not a nutrient, but it’s sold over the counter in most countries as a dietary supplement for sleep. It’s used both as a sleep-onset aid and as a circadian rhythm regulator in hospital and clinical settings.²⁴ One of the most common mistakes people make with melatonin is taking too much too late. A dose-response meta-analysis found that melatonin’s effect on reducing the time it takes to fall asleep and increasing total sleep time peaks at about 4 mg per day, and that taking it roughly three hours before the desired bedtime is more effective than the common practice of taking it 30 minutes before bed.²⁵ Research in pediatric populations with neuropsychiatric conditions found similar optimal dosing, with the greatest benefits appearing between 2 and 4 mg, again taken well before bedtime.²⁶ If you’ve tried melatonin at 10 mg right before bed and found it useless, the dose and timing may have been the problem, not the supplement itself.

Probiotics

Probiotic supplements contain live microorganisms, usually strains of Lactobacillus or Bifidobacterium, intended to support gut health. The proposed mechanisms are broad: probiotics may help restore a healthier balance of gut bacteria, modulate the immune system, and even influence neurological function through the gut-brain axis.²⁷ The challenge with probiotics is that “probiotic” is a category, not a single product. Different strains do different things. A strain with evidence for preventing antibiotic-associated diarrhea may do nothing for irritable bowel syndrome, and vice versa. Buying a generic probiotic off the shelf and expecting targeted results is a bit like walking into a pharmacy and grabbing any random prescription bottle. The specificity matters, and most labels don’t make it easy to match the strains in the bottle to the condition you’re trying to address.

NAD+ Precursors

Nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) are newer supplements that have gained attention in the longevity and anti-aging community. Both are precursors to NAD+, a molecule involved in energy metabolism and DNA repair that declines with age. Supplementing with either NMN or NR has been shown to raise NAD+ levels.²⁸ The idea is that boosting NAD+ could slow or partially reverse some aspects of physiological decline associated with aging.²⁹ The animal data is intriguing, but the human evidence is still thin. Most human trials have been small and short, and while they confirm that blood NAD+ levels go up, whether that translates into meaningful health improvements over years remains an open question. These supplements are expensive, and the science is at the “promising hypothesis” stage rather than the “proven benefit” stage.

Quality and Safety Concerns That Cut Across Categories

Because supplements skip premarket approval, quality varies widely. Independent testing has found heavy metals, undeclared pharmaceutical ingredients, stimulants, and other contaminants in commercial products.³⁰ The problem isn’t limited to shady brands — even products from mainstream retailers have occasionally failed third-party testing for label accuracy or purity. Multiple companies now offer third-party certification programs to fill this gap, but each program has its own testing standards, and it’s difficult for consumers to assess whether a given certification actually reduces the risk enough to trust the product.³¹ Looking for seals from established testing organizations (NSF International, USP, Informed Sport) is the most practical step you can take, but it’s worth understanding that certification means the product was tested and met certain standards — it doesn’t guarantee the supplement will work for your intended purpose.

The Placebo Problem in Supplement Research

One complication worth mentioning is how hard it is to study supplements rigorously. Placebo effects are powerful in supplement research, especially for subjective outcomes like pain, stress, or sleep quality. A study examining sham supplements for weight loss found that participants who believed they were taking a real supplement experienced measurable changes, and raised the concern that placebo-controlled supplement trials may overestimate the real effect of the active ingredient because even the placebo pill creates expectations that “no pill at all” does not.³² This doesn’t mean all supplement benefits are placebo, but it does mean that the glowing personal testimonials you read online should be taken with a grain of salt. The gold standard remains well-designed randomized trials, and for many popular supplements, those trials are either small, few in number, or contradictory.

1
Journal of Public Policy & Marketing. Drugs or Dietary Supplements: FDA’s Enforcement of DSHEA ↩︎
2
The Journal of Nutrition. Twenty Years of the Dietary Supplement Health and Education Act—How Should Dietary Supplements Be Regulated? ↩︎
3
PubMed Central. Fat-soluble vitamins in food supplements: do the labels follow the recommended doses? ↩︎
4
PubMed Central. Vitamin D and Calcium in Osteoporosis, and the Role of Bone Turnover Markers: A Narrative Review of Recent Data from RCTs ↩︎
5
PubMed. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older ↩︎
6
PubMed Central. The importance of vitamin B12 for individuals choosing plant-based diets ↩︎
7
PubMed Central. Intake of vitamin B12 in relation to vitamin B12 status in groups susceptible to deficiency: a systematic review ↩︎
8
PubMed Central. Exploring Vitamin B12 Supplementation in the Vegan Population: A Scoping Review of the Evidence ↩︎
9
PubMed Central. Ferrous Sulfate Supplementation Causes Significant Gastrointestinal Side-Effects in Adults: A Systematic Review and Meta-Analysis ↩︎
10
PubMed. Magnesium and blood pressure regulation: systemic and renal mechanisms ↩︎
11
PubMed Central. The Effects of Fish Oil on Cardiovascular Diseases: Systematical Evaluation and Recent Advance ↩︎
12
European Heart Journal. Fish oil and omega-3 fatty acids in cardiovascular disease: do they really work? ↩︎
13
PubMed. St John’s wort: a systematic review of adverse effects and drug interactions for the consultation psychiatrist ↩︎
14
PubMed Central. The Effects of St. John’s Wort and its Interactions with SSRI’s ↩︎
15
The Journal of Pharmacology and Experimental Therapeutics. Inhibition of Human Cytochrome P450 Enzymes by Constituents of St. John’s Wort, an Herbal Preparation Used in the Treatment of Depression ↩︎
16
PubMed Central. The spice for joint inflammation: anti-inflammatory role of curcumin in treating osteoarthritis ↩︎
17
PubMed. Curcumin in turmeric: Basic and clinical evidence for a potential role in analgesia ↩︎
18
PubMed Central. Effects of Ashwagandha Supplements on Cortisol, Stress, and Anxiety Levels in Adults: A Systematic Review and Meta-Analysis ↩︎
19
PubMed Central. An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract ↩︎
20
PubMed Central. A standardized Ashwagandha root extract alleviates stress, anxiety, and improves quality of life in healthy adults by modulating stress hormones: Results from a randomized, double-blind, placebo-controlled study ↩︎
21
PubMed Central. Effects of whey protein supplementation prior to, and following, resistance exercise on body composition and training responses: A randomized double-blind placebo-controlled study ↩︎
22
PubMed Central. Effects of creatine supplementation on cognitive function of healthy individuals: A systematic review of randomized controlled trials ↩︎
23
PubMed Central. Collagen supplementation in skin and orthopedic diseases: A review of the literature ↩︎
24
PubMed Central. Melatonin dose and timing: Do we have it right? ↩︎
25
PubMed. Optimizing the Time and Dose of Melatonin as a Sleep-Promoting Drug: A Systematic Review of Randomized Controlled Trials and Dose-Response Meta-Analysis ↩︎
26
PubMed. Optimizing timing and dose of exogenous melatonin administration in neuropsychiatric pediatric populations: a meta-analysis on sleep outcomes ↩︎
27
PubMed Central. Effects of probiotics on gut microbiota: mechanisms of intestinal immunomodulation and neuromodulation ↩︎
28
Food Frontiers. An Updated Review on the Mechanisms, Pre‐Clinical and Clinical Comparisons of Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR) ↩︎
29
PubMed Central. NAD+ Precursors Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR): Potential Dietary Contribution to Health ↩︎
30
PubMed. Contamination and adulteration of food supplements: Risk perception and regulatory awareness in recreational athletes ↩︎
31
PubMed. Essential Features of Third-Party Certification Programs for Dietary Supplements: A Consensus Statement ↩︎
32
PubMed Central. Expectancy, self-efficacy, and placebo effect of a sham supplement for weight loss in obese subjects ↩︎