Dietary supplements: a scientific review

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.

Why take them? Targets and populations

• 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.

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

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.

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

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.

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

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.

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