Vitamin, mineral & supplement reference

Reviewed entry

Vitamin D3

How it works in the body: Fat-soluble D3 is absorbed with dietary fat, converted in the liver to 25-hydroxyvitamin D, then activated mainly in kidneys. It helps regulate calcium and phosphate absorption and bone mineralisation.
What it may improve: Correcting inadequate status and supporting bone health; benefits outside deficiency depend on the outcome and population.
When and with what: Food containing fat; morning or evening is a preference. Consider calcium intake from food.
Amount and context: Adult recommended intake is commonly 600 IU (15 µg) through age 70 and 800 IU (20 µg) after 70. A blood test can guide treatment when deficiency is suspected.
Higher-dose evidence and limits: Trials of 4,000 IU/day for diabetes prevention did not establish broad prevention. The adult upper limit is 4,000 IU/day unless supervised; more can cause high calcium.

Reviewed entry

How it works in the body: A cofactor in hundreds of enzyme reactions, including energy production, nerve signalling and muscle contraction. The gut absorbs it and the kidneys regulate excess.
What it may improve: Meeting needs supports normal function; sleep benefit from extra magnesium in people without deficiency is less certain.
When and with what: With food if it upsets the stomach. Glycinate and citrate are formulations; count elemental magnesium across both.
Amount and context: Adult dietary requirements vary by age and sex, roughly 310–420 mg/day from all sources. Supplement amount is a separate decision.
Higher-dose evidence and limits: The U.S. adult upper limit of 350 mg/day applies to supplemental magnesium, not food. Higher doses are used medically for specific conditions, with monitoring; they are not a proven general sleep upgrade.

Reviewed entry

How it works in the body: Absorbed in the small intestine and used by enzymes, immune signalling, wound repair and gene expression. The body has no specialised long-term zinc store.
What it may improve: Corrects low intake; zinc lozenges have been studied for shortening colds, with product and timing differences.
When and with what: Food can reduce nausea; separate from certain antibiotics. Consider copper status if a clinician prescribes extended high doses.
Amount and context: Adult recommended intake is about 8 mg/day for women and 11 mg/day for men.
Higher-dose evidence and limits: High-dose zinc is not a routine immune strategy. The adult upper limit is 40 mg/day from all sources; sustained excess can produce copper deficiency.

Reviewed entry

How it works in the body: A water-soluble antioxidant and enzyme cofactor required to make collagen and carnitine. It improves absorption of non-heme iron from plant foods.
What it may improve: Prevents deficiency and helps normal tissue repair; regular supplementation may modestly shorten colds in some studies but does not reliably prevent them in the general population.
When and with what: Any time; combine plant iron foods with citrus or capsicum. Food-first intake is practical.
Amount and context: Adult recommended intake is 75 mg/day for women and 90 mg/day for men; smokers need more.
Higher-dose evidence and limits: Gram-dose trials have not established a general longevity benefit. The adult upper limit is 2,000 mg/day; gastrointestinal upset and kidney-stone considerations matter.

Reviewed entry

How it works in the body: EPA and DHA incorporate into cell membranes and contribute to signalling molecules that regulate inflammation and lipid metabolism.
What it may improve: Fish intake and prescription formulations have different evidence. Specific high-dose prescription EPA can help selected cardiovascular-risk groups; triglycerides can fall at therapeutic doses.
When and with what: With a meal. Read the actual EPA and DHA content, not only total fish-oil milligrams.
Amount and context: There is no single universal EPA/DHA supplement dose for healthy adults; dietary fish guidance and individual goals differ.
Higher-dose evidence and limits: Prescription 4 g/day regimens are studied for high triglycerides and selected risks, but are not equivalent to over-the-counter capsules. Higher-dose trials also signal atrial-fibrillation risk in some groups.

Reviewed entry

How it works in the body: Muscle and brain cells convert creatine to phosphocreatine, a rapid reserve for regenerating ATP during short, intense effort.
What it may improve: Strongest evidence is for repeated high-intensity effort and resistance-training gains. Cognition findings are interesting but mixed.
When and with what: Daily consistency matters more than a clock time; take with food if preferred. Pair with progressive training and adequate protein.
Amount and context: Studies commonly use 3–5 g/day maintenance in adults. A loading phase is optional, not required for eventual saturation.
Higher-dose evidence and limits: Some studies use 20 g/day divided for 5–7 days to load stores faster; this is not evidence that chronic 20 g/day gives extra benefit. Discuss kidney disease or abnormal lab values with a clinician.

Reviewed entry

How it works in the body: Absorbed after stomach acid releases it from food and intrinsic factor enables uptake in the ileum. It supports red blood cells, myelin and DNA synthesis.
What it may improve: Correcting deficiency can reverse anaemia and prevent neurologic harm. Vegans and some older adults are at higher risk.
When and with what: Any time; oral, sublingual and injections serve different clinical situations. Metformin and acid-suppressing medicines can affect status.
Amount and context: Adult recommended intake is 2.4 µg/day; deficiency treatment often uses much larger oral doses or injections under clinical direction.
Higher-dose evidence and limits: Large doses are sometimes used because only a fraction is absorbed. There is no established upper limit, but extra B12 does not reliably boost energy when status is adequate.

Reviewed entry

How it works in the body: Heme and non-heme iron enter through the gut, travel on transferrin and support haemoglobin, oxygen transport and energy enzymes. Hepcidin regulates absorption.
What it may improve: Iron replacement helps iron-deficiency anaemia and may improve fatigue when deficiency is established. Too much iron can be harmful.
When and with what: Vitamin C-rich food can improve non-heme absorption. Tea, coffee, calcium and some medicines can interfere; dosing schedules should follow a clinician's plan.
Amount and context: As dietary reference points, adults 19–50 need about 8 mg/day (men) or 18 mg/day (women); pregnancy raises the need. Blood counts and ferritin should guide iron supplements rather than a universal pill dose.
Higher-dose evidence and limits: Therapeutic elemental iron doses are higher than dietary requirements and can cause gastrointestinal effects. There is no reason to take high-dose iron without a clear indication.