Dietary supplements: a scientific review

By Ichrak Haddad•1/31/2026
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Table of Contents

What is a dietary supplement?

Product intended to complement the diet with nutrients or bioactive substances (vitamins, minerals, amino acids, extracts). Available as capsules, tablets, powders or liquids; not medicines.

  • Vitamins, minerals, omega‑3, amino acids, plants
  • Forms: capsules, powders, liquids

Why take them? Targets and populations

Indications: documented deficiencies, increased needs (pregnancy, older adults), specific sports goals or micronutritional support. Some preventive uses (vitamin D, calcium) are evidence‑supported; many wellness claims lack robust proof.

  • Documented deficiencies
  • Pregnancy, breastfeeding, older adults
  • Specific sports goals

Types of supplements

Nutrients (vitamins, minerals), fatty acids (omega‑3), proteins and creatine, plant extracts, probiotics and novel ingredients (peptides, nutrigenomics). Efficacy and safety vary widely by ingredient and product quality.

  • Vitamins and minerals
  • Proteins, creatine, BCAA
  • Plants, probiotics, innovations

Supplements in sports

Commonly used by recreational and competitive athletes. Strong evidence: creatine for strength/power, whey protein to meet protein needs; HMB and electrolytes in specific contexts. Watch for contaminants and banned substances.

  • Commonly used by recreational and competitive athletes
  • Strong evidence: creatine for strength/power, whey protein to meet protein needs
  • HMB and electrolytes in specific contexts
  • Watch for contaminants and banned substances

Market trends and innovations

Market growth, convenient formats (gummies, sprays), personalization (DNA, microbiome), postbiotics and micro‑encapsulation for better bioavailability. Viral marketing often outpaces scientific evidence.

  • Market growth, convenient formats, personalization, postbiotics, micro‑encapsulation
  • Viral marketing often ahead of scientific evidence

Scientific evidence: proofs and limits

Some interventions (vitamin D + calcium, creatine, omega‑3, proteins) have clinical trial support. Many plant extracts and formulations have limited or conflicting evidence; multivitamins do not increase longevity in well‑nourished populations.

  • Some interventions (vitamin D + calcium, creatine, omega‑3, proteins) have clinical trial support
  • Many plant extracts and formulations have limited or conflicting evidence
  • multivitamins do not increase longevity in well‑nourished populations

Risks, interactions and vigilance

Risks of overdose (fat‑soluble vitamins, iron), drug interactions (herbal extracts), contaminants and doping risk. Importance of certified products (Informed‑Choice, NSF) and prescribing based on clinical and biological assessment.

  • Risks of overdose (fat‑soluble vitamins, iron), drug interactions (herbal extracts), contaminants and doping risk
  • Importance of certified products (Informed‑Choice, NSF) and prescribing based on clinical and biological assessment

When and how to prescribe in practice

Clear indications: documented deficiency, increased needs (pregnancy, older adults), sports goals with deficits. Approach: dietary assessment, targeted labs, choose certified products, set clear objectives and regular follow‑up.

  • Clear indications: documented deficiency, increased needs (pregnancy, older adults), sports goals with deficits
  • Approach: dietary assessment, targeted labs, choose certified products, set clear objectives and regular follow‑up

Practical conclusion

Supplements can be useful in specific, documented contexts; they do not replace a balanced diet. The nutritionist’s role is central to assess, prescribe safely and monitor supplement use.

  • Supplements can be useful in specific, documented contexts
  • they do not replace a balanced diet
  • The nutritionist’s role is central to assess, prescribe safely and monitor supplement use

Scientific references

NIH Office of Dietary Supplements; ANSES – dietary supplements; FAO safety alerts; systematic reviews on creatine, omega‑3, vitamin D; market reports 2024–2025.

  • NIH Office of Dietary Supplements
  • ANSES – Dietary supplements
  • FAO – Safety alerts
  • Systematic reviews on creatine, omega‑3, vitamin D
  • Market reports 2024–2025