Do you need them?

What does the food-first principle say?

TÜBER 2022 states that dietary supplements contribute to nutrition but that none replaces an adequate and balanced diet and that the basic goal is to meet nutrient requirements from food first. It adds that supplements may be used where requirements cannot be met for various reasons. ^[1] Labels of dietary supplements in Türkiye have a parallel rule: Communiqué 2013/49 prohibits statements on the label, presentation and advertising of a dietary supplement that state, imply or stress that nutrients cannot be met by an adequate and balanced diet. ^[3]

As examples of nutritional inadequacy, TÜBER gives the following situations: following a low-energy diet, excluding one or more food groups from the diet, being unable to consume enough food because of loss of appetite, illness or socioeconomic reasons, or being unable to eat a balanced diet despite adequate energy intake. ^[1] This statement shows that the rationale for a supplement depends on a particular gap, not on the person.

What does the evidence say for the general population?

USPSTF evaluated the effect of individual nutrients, functionally related nutrient pairs and multivitamins on preventing cardiovascular disease and cancer in nonpregnant adults living in the community. It was determined with moderate certainty that the harms of beta-carotene supplementation outweigh the benefits and that vitamin E provides no net benefit; a recommendation against both (grade D) was given. For multivitamins and for single or paired nutrients other than beta-carotene and vitamin E, the balance of benefits and harms could not be determined because of lack of evidence (I statement). ^[2] This statement covers supplements used for prevention, not people with a deficiency.

The results of multivitamins in randomized trials are explained in a separate guide: on the page Is a multivitamin necessary?, the PHS II trial in male physicians, COSMOS and the mortality results of three US cohorts are given with their sources.

For whom is there an evidence-based rationale for a supplement?

Section 9.2.4 and Table 9.2 of TÜBER 2022 give these groups and the national programs run by the Ministry of Health as follows.

TÜBER gives two limiting notes in the same section: iron support is generally not recommended in postmenopausal women and adult men; smokers are advised to avoid beta-carotene support. ^[1] That is, belonging to a group does not mean a supplement is needed for every nutrient.

What does the international guideline say about vitamin D?

The Endocrine Society 2024 guideline recommends “empiric” supplementation (without testing, above the reference intake) for people with no established indication for vitamin D treatment or 25(OH)D testing in children and adolescents aged 1–18, in adults aged 75 and over, in pregnant women and in people with high-risk prediabetes; it recommends against empiric supplementation above the reference intake in healthy adults under 75. The guideline’s recommendations are at the “suggest” level, that is, conditional recommendations; the guideline also writes that the optimal empiric dose remains uncertain in these groups because doses in studies vary widely. ^[4] This statement is a different framework from TÜBER’s programs in Türkiye, and the two should be read side by side: one describes a national public health program, the other a clinical guideline for empiric supplementation.

Are there supplements with evidence for performance?

The IOC 2018 consensus statement says that supplements claimed to directly or indirectly improve performance are the largest group of products marketed to athletes but that only a few (caffeine, creatine, certain buffering agents and nitrate) have good evidence of benefit. The statement also says that response can vary widely from person to person and that a complete nutrition assessment should be done before supplement decisions. ^[5]

For creatine, the ISSN 2017 position stand states that the supplement increases intramuscular creatine level and is associated with improvements in high-intensity exercise performance; it also reports that short- and long-term use for up to 5 years is safe and well tolerated in healthy people. ^[6] For protein, ISSN 2017 states that a total protein intake of 1.4–2.0 g/kg/day is sufficient for increasing and maintaining muscle mass in most people who exercise; it says that physically active people can meet their daily protein requirement with whole foods and that supplements are a practical way to ensure adequate protein quality and amount. ^[7] These statements cover healthy people who exercise. Product-based results are in the guides Creatine and Protein powder, and the general framework for athletes is on the page Supplements for athletes.

Which questions structure the supplement decision?

In place of a personal recommendation, these are the questions that structure the decision, and each is covered with its sources in a separate place on this site:

1. Is there a documented deficiency or a defined risk group? The table above lists these groups according to TÜBER.
2. Can the requirement be met from food? The food-first principle considers a supplement for the part that cannot be met from food. ^[1]
3. What outcome is targeted, and what is its evidence grade? For prevention goals, general-population evidence is insufficient or negative (USPSTF); for performance goals, the evidence depends on the product (IOC).
4. Is total intake below the upper limit? Upper limits are for the daily total from all sources; details are in the guide Are supplements safe?.
5. Is there illness or medicine use? TÜBER requires that supplements be used under physician supervision in this case; interactions are on the page Drug interactions.

When is a test informative?

A blood test is meaningful to the extent that it can answer “how deficient” in a supplement decision; not every test has the same value for everyone. For vitamin D, the Endocrine Society 2024 guideline gives a conditional recommendation against routine 25(OH)D testing in people without an established indication; it states that there is no clinical trial evidence for routine screening in the healthy general population, in people with obesity or in people with dark skin. ^[4] Testing is therefore meaningful when there are symptoms, a risk group or a defined indication. The interpretation of ferritin, 25(OH)D and B12 results, laboratory thresholds, the conditions under which they are measured and misleading situations are explained with their sources in the relevant guides:

• What should ferritin be? — ferritin and iron stores
• What should vitamin D be? — 25(OH)D values and units
• What should B12 be? — B12 level and additional tests

Where next after this guide?

For what a supplement is, see What are supplements?; for how to read a label, How to read a label; for timing, When to take supplements. This guide does not recommend a personal product or dose; in pregnancy, childhood, chronic illness or medicine use, the supplement decision is made with a physician or pharmacist.