Supplements — an evidence-first decision guide

Nutrition and lifestyle first. Supplements are considered for a confirmed deficiency, a clear risk group or a well-supported indication, with expected benefit, dose, safety and follow-up made explicit.

Evidence guide

• Creatine monohydrate — One of the best-supported performance supplements when combined with resistance training. Adults doing progressive resistance training; particularly useful when preserving or gaining strength and lean mass matters. Water-weight gain is common. Seek clinical advice with kidney disease, pregnancy or complex medication use.
• Protein powder — Convenient food, not a special drug; useful when normal meals do not cover a suitable protein intake. People who struggle to meet protein needs, including some older adults, athletes and people with low appetite. Choose a product compatible with allergies and digestion. Individual advice may be needed in advanced kidney disease.
• Psyllium husk — A food-derived soluble fibre with useful evidence for constipation and modest LDL-cholesterol reduction. Adults with low fibre intake, constipation or a defined goal to modestly reduce LDL cholesterol. Increase gradually, take with enough fluid and separate from medicines when advised; investigate alarm symptoms.
• Folic acid — Proven prevention for neural-tube defects before conception and in early pregnancy. People who could become pregnant, beginning before conception and continuing in early pregnancy according to local guidance. Avoid unsupervised high doses; check vitamin B12 context when clinically relevant.
• Vitamin B12 — Essential and highly useful for predictable low-intake or malabsorption risk and confirmed deficiency. Vegans, people with relevant malabsorption, some older adults, and users of medicines that can impair status. Investigate symptoms rather than masking them; route and dose depend on cause and severity.
• Iron — Effective for confirmed iron deficiency; inappropriate routine use can cause harm. People with confirmed deficiency or a clinician-defined high-risk situation. Gastrointestinal effects, overdose risk and iron overload matter; keep away from children.
• Iodine — Essential, but supplementation is mainly a diet- and life-stage decision rather than a universal habit. People with low iodine intake and selected pregnancy/lactation contexts according to national guidance. Excess can disturb thyroid function; thyroid disease needs individual advice.
• Vitamin D — Correct deficiency and follow Swiss population guidance; do not turn routine testing into a universal rule. People covered by national supplementation guidance, those with a defined deficiency or a specific clinical risk. Chronic high doses can cause hypercalcaemia. Vitamin K2 is not automatically required.
• Omega-3 (EPA/DHA) — Food first; targeted use depends on diet, pregnancy context or a defined triglyceride indication. People with low oily-fish intake; selected pregnancy contexts; patients treated for high triglycerides under clinical guidance. High doses can increase bleeding or atrial-fibrillation concerns in some contexts; product oxidation and dose accuracy matter.
• Zinc — Useful for confirmed deficiency; zinc lozenges may modestly shorten a cold when started early, but do not prevent colds reliably. People with deficiency risk; adults considering a short, early lozenge course for a common cold. Long-term high doses can cause copper deficiency; intranasal zinc should be avoided.
• Calcium — Calcium is essential; a calcium pill is useful mainly to close a demonstrated dietary gap or as part of a defined clinical plan. People whose diet cannot meet needs and patients with an individually defined bone-health plan. Constipation, kidney-stone context and interactions matter; avoid unnecessary large bolus doses.
• Magnesium — Correct a true deficiency; blanket claims for sleep, cramps, blood pressure or glucose control are stronger than the evidence. People with low intake, relevant losses, malabsorption or medicines that affect magnesium; other uses require a specific goal. Diarrhoea is common; kidney impairment can make accumulation dangerous. Separate from interacting medicines.
• Vitamin K2 — Plausible biology and surrogate-marker studies have not established routine K2 supplementation for cardiovascular or fracture prevention. No general healthy-adult group has a proven routine indication; clinical use requires an individual reason. Vitamin K can materially interfere with vitamin-K-antagonist anticoagulation.
• Multivitamins — Can cover selected intake gaps, but do not reliably prevent cardiovascular disease, cancer or death in healthy replete adults. Only when a dietary assessment identifies multiple predictable gaps or a clinician recommends a specific formulation. Formulations vary; excess vitamin A, B6, iron or other ingredients can matter.
• Vitamin C — Essential nutrient, but routine high-dose supplementation does not prevent colds for most people. People with low intake or deficiency; selected extreme-exercise contexts may differ. High doses commonly cause gastrointestinal symptoms and can be relevant in kidney-stone risk.