What Are Supplements: Complete Beginner's Guide

Dietary supplements in three numbers

Three study figures show how common dietary supplements are, and how often they are not what the label says.

Study figures come from PubMed papers. Where a point is practice rather than a trial, we say so.

What this dietary supplements guide covers

What are supplements? The definition

Dietary supplements are commercially available products consumed as an addition to the usual diet (PMID 26442916).

They include vitamins, minerals, herbal and complementary products, protein, amino acids and performance products such as creatine (PMID 26465986, 29540367).

In the United States, supplements are sold as a category of food, not as drugs. Makers do not need approval before sale, and the FDA acts after a problem is found (PMID 30646238).

The IOC consensus sorts dietary supplements by purpose. They fix a micronutrient deficiency, give convenient energy, boost performance directly, or support heavy training (PMID 29540367).

Who takes dietary supplements

Use is rising. Among 29,216 US adults, any supplement use rose from 51.8% in 2011 to 2012 to 61.4% in 2021 to 2023 (PMID 41128907).

Stacking is rising faster. Use of four or more products went from 10.0% to 16.2% in the same period (PMID 41128907).

Athletes use more. A meta-analysis of 159 studies found elite athletes used dietary supplements far more than non elite athletes. Athletes also used more than the general population (PMID 26442916).

Men used protein and creatine more often than women; women used iron more often (PMID 26442916).

Types of dietary supplements

Do dietary supplements work?

Some do, most do not. The IOC consensus says nutrition makes a small contribution to elite performance, and dietary supplements a minor part of that (PMID 29540367).

Of the performance products, only a few have good evidence: caffeine, creatine, specific buffering agents and nitrate (PMID 29540367).

Responses vary widely between people because of genetics, the microbiome and habitual diet (PMID 29540367).

The biggest category, multivitamins, showed no mortality benefit in 390,124 adults followed up to 27 years (PMID 38922615).

The proven few: what the position stands say

Creatine. It raises muscle creatine and improves high intensity performance. Up to 30 g a day for 5 years was safe in healthy people (PMID 28615996).

Caffeine. 3 to 6 mg per kg improves performance in most but not all studies, with the most consistent benefit in aerobic endurance (PMID 33388079).

Beta alanine. 4 to 6 g a day for at least 2 to 4 weeks improves performance in efforts lasting 1 to 4 minutes (PMID 26175657).

Protein. Across 49 trials with 1,863 people, extra protein added 0.30 kg fat free mass and 2.49 kg to one rep max. Gains stopped above about 1.6 g per kg a day (PMID 28698222).

How dietary supplements are regulated

US law treats dietary supplements as food. The maker is responsible for safety and labelling, and no approval is needed before a product reaches the shelf (PMID 30646238).

The FDA steps in afterwards. From 2007 through 2016 it identified 776 adulterated dietary supplements from 146 companies (PMID 30646238).

Warnings do not always end it. 28 products were named in 2 or 3 warnings more than 6 months apart. 19 of them had new hidden ingredients each time (PMID 30646238).

For athletes, a tainted supplement can mean a doping violation. The IOC lists inadvertent ingestion of prohibited substances as a known risk (PMID 29540367).

Hidden drugs in dietary supplements

Most adulterated products were sold for sexual enhancement (45.5%), weight loss (40.9%) or muscle building (11.9%) (PMID 30646238).

The hidden ingredient matched the claim. Sildenafil was in 47.0% of sexual products and sibutramine in 84.9% of weight loss products. Synthetic steroids were in 89.1% of muscle products (PMID 30646238).

Ordinary products are not immune. Of 634 non hormonal dietary supplements bought in 13 countries, 14.8% contained anabolic steroids not on the label (PMID 14986195).

Products sold as SARMs ranged from no active ingredient at all to undeclared prohibited compounds. Measured doses did not match the packaging (PMID 32748554).

Are dietary supplements safe?

Mostly, with a measurable exception. US emergency departments see an estimated 23,005 visits a year for supplement adverse events, with 2,154 hospitalisations (PMID 26465986).

Young adults aged 20 to 34 are over represented. Weight loss or energy products caused 71.8% of visits for palpitations, chest pain or fast heart rate (PMID 26465986).

Herbal and complementary products accounted for 65.9% of single supplement visits; vitamins and minerals for 31.8% (PMID 26465986).

6 rules for judging dietary supplements

1. Fix the diet first. The IOC advises a full nutritional assessment before any supplement decision (PMID 29540367).

2. Check the proven list. Caffeine, creatine, buffers and nitrate have good evidence; most others do not (PMID 29540367).

3. Expect small effects. Protein added 0.30 kg fat free mass over months of lifting (PMID 28698222).

4. Distrust big promises. Sexual, weight loss and muscle products made up 98.3% of adulterated supplements (PMID 30646238).

5. Trial it in training. The IOC says test any performance supplement before using it in competition (PMID 29540367).

6. Count the bottles. Practice, not studied: more products means more chances of a hidden ingredient and less chance of knowing which one worked.

Verdict: 7 facts about dietary supplements

1. Most adults take them. 61.4% of US adults in 2021 to 2023 (PMID 41128907).

2. Few are proven for performance. Caffeine, creatine, buffers, nitrate (PMID 29540367).

3. Protein helps a little. +0.30 kg fat free mass, +2.49 kg strength (PMID 28698222).

4. Multivitamins did not extend life. No mortality benefit in 390,124 adults (PMID 38922615).

5. Nobody checks before sale. The FDA found 776 adulterated products after the fact (PMID 30646238).

6. Hidden steroids are common. 14.8% of ordinary supplements in one study (PMID 14986195).

7. Fat burners send people to the ER. 71.8% of heart symptom visits (PMID 26465986).