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Supplement Timing & Use Cheat Sheet

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Last updated September 2026

In one pass Taking a supplement is not done once you swallow it.

Educational content, not medical advice — consult a clinician.

Chapter 1

When to take each supplement

Taking a supplement is not done once you swallow it. When you take it directly affects how much you absorb and how many side effects you get. Common supplements fall into four groups by timing: with meals, on an empty stomach, by the clock, and any time.

With a meal that contains fat
Fat-soluble vitamins A, D, E and K: they need dietary fat to be absorbed.Fish oil ( and , two omega-3 fats): taking it with food cuts down on fishy burps.Coenzyme (the reduced form, ubiquinol): fat-soluble, so it is absorbed better with food.Curcumin: with meals, especially together with fat and black pepper.
On an empty stomach (1 hour before or 2 hours after a meal)
Iron: absorbed best on an empty stomach. If your stomach cannot take it, you can switch to taking it with food, though you will absorb somewhat less.Levothyroxine: must be taken on an empty stomach, 4 hours apart from calcium and iron; drink coffee no sooner than 1 hour after the pill.Some probiotics (acid-resistant strains): they pass through the stomach faster when it is empty.Collagen peptides: empty stomach or with food, no strict rule.
If there are children at home, remember one thing first: iron tablets are one of the most common causes of acute poisoning in children. If you suspect a child has swallowed iron tablets, do not wait at home for symptoms; contact poison control or go to the emergency department now.

In practice · Morning, bedtime and any time

Morning
B vitamins (B1, B2, B6, B12, folate): they take part in energy metabolism, and taking them in the morning does not disturb sleep.Coenzyme : some people find it mildly stimulating, and some report insomnia when they take it in the evening.Iron (if once a day): absorbed best on an empty stomach, 30–60 minutes before breakfast.Zinc (with breakfast if it makes you nauseous): high doses on an empty stomach can upset the stomach.
Evening or before bed
Magnesium (glycinate, threonate): often used to relax and to help sleep; the evidence for this is limited.Melatonin: 30–60 minutes before bed, at 0.3–1 mg (not 5–10 mg).Glycine: 3 g before bed; a small trial found better self-rated sleep quality.Ashwagandha: usually in the evening or split into two doses; it has a calming effect.Calcium (if once a day): bone turnover is active at night, but the evidence is weak; splitting the dose matters more.
Any time (just keep it the same each day)
Creatine: 3–5 g a day at any time; slightly better with carbohydrate or protein.Beta-alanine: split into doses of 0.8–1.6 g; taking it with meals reduces the skin tingling.Vitamin C: split doses; with meals if your stomach is sensitive.Electrolyte powder: during or after exercise, or as needed in hot weather.

Mechanism · Why fat-soluble vitamins need food

Vitamins A, D, E and K, along with fish oil, coenzyme and curcumin, are fat-soluble: they do not dissolve in water and have to dissolve in fat before the gut can absorb them. Taking a vitamin capsule on an empty stomach is like pouring oil onto a dry plate; the gut carries away much less of it.

One figure: Mulligan 2010 followed 17 bone-clinic patients whose vitamin D treatment was not working and had them take it with the largest meal of the day instead. After 2–3 months, their blood (the lab value that reflects the body's vitamin D stores) had risen by 56.7% on average. It was a before-and-after comparison with no control group, so trust the direction but do not copy the size. You also do not need much fat: an egg, a few slices of avocado or a spoon of olive oil in the meal is enough.

Water-soluble vitamins (the B group and C), on the other hand, do not need fat, but split doses work better than one big dose: the body can only absorb a limited amount at a time, and the rest leaves in the urine.

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Mechanism · Why some doses should be split

Many supplements are best split rather than taken all at once, for two reasons:

1. The absorption ceiling: calcium is absorbed best in doses of no more than about 500 mg of elemental calcium, so a larger daily amount is split into two.

Iron is the counterexample, so do not copy the rule: a large single dose is absorbed at a lower percentage, but splitting the same amount into two doses a day did not increase absorption, and it pushed up hepcidin, the hormone that blocks iron uptake, even further. In a small study of iron-deficient women (Stoffel 2017), taking iron every other day was absorbed at a higher percentage than taking it daily. So iron is usually taken at most once a day; whether to switch to every other day is a question for your doctor.

Zinc does not depend on splitting either: more than 40 mg a day over the long term (the adult tolerable upper intake level) interferes with copper absorption. That is about the daily total, and splitting it does not help.

2. Side-effect peaks: 4–6 g of Beta-alanine in one go almost always causes skin tingling (called paresthesia, and harmless), while 0.8–1.6 g four times a day is barely noticeable. High-dose vitamin C taken at once can cause diarrhea, which splitting avoids. More than 25 mg of zinc on an empty stomach can cause nausea, and split doses with food are easier.

The exception: creatine does not need splitting. 3–5 g once a day with a meal is fine, because the body has a dedicated transporter for it and no practical absorption ceiling.

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Chapter 2

Which to pair and which to separate

Supplements do not each go their own way. Some help each other when taken together; others compete for the same channel. These are the most common rivals.

Rivals to keep apart
Calcium and iron: calcium inhibits iron absorption, so take them at least 2 hours apart.Calcium and zinc: high-dose calcium inhibits zinc absorption.Zinc and copper: long-term zinc (>25 mg/day) makes the gut wall produce more of a protein called metallothionein, which binds copper and eventually causes copper deficiency. Long-term zinc should come with 1–2 mg of copper.Zinc and iron: at high doses they compete, most noticeably when liquid preparations are taken on an empty stomach.Iron and tea or coffee: their tannins inhibit the absorption of non-heme iron (the iron in plants and supplements). A cup of black tea with a meal can cut that meal's absorption by 79–94%, so keep them 2 hours apart.Iron and milk or calcium supplements: the same applies.Levothyroxine and calcium or iron: keep them 4 hours apart; have coffee and breakfast no sooner than 1 hour after the pill.Vitamin E and anticoagulants (warfarin): vitamin E has a mild anticoagulant effect and raises bleeding risk.
Inhibitors in food
Non-heme iron with tea, coffee or cocoa (tannins)Non-heme iron with high-calcium foods (milk, cheese)Non-heme iron with high-phytate foods (whole grains, legumes; fermenting or soaking lowers phytate)

Mechanism · Which pairs help each other

Pairs that help each other
Iron and vitamin C: vitamin C reduces ferric iron to the more absorbable ferrous form, clearly raising absorption.Vitamin D and magnesium: magnesium is a cofactor for both of vitamin D's hydroxylations (a hydroxyl group is added in the liver and again in the kidney to make the active form), so without enough magnesium vitamin D cannot be fully activated.Vitamin D and : by the mechanism, proteins activated by K2 help deposit calcium in bone and keep it away from vessel walls; evidence on outcomes in people is limited.Vitamin D and calcium: vitamin D promotes calcium absorption, but take no more than 500 mg of calcium at a time.Curcumin and piperine: piperine blocks the liver's breakdown of curcumin, and in a pharmacokinetic study in human volunteers it raised bioavailability 20-fold (Shoba 1998). More in the blood does not mean a 20-fold stronger effect.Beta-alanine and creatine: they work on different energy systems and do not compete.Folate and B12: partners in one-carbon metabolism. If you are short of B12 and take large doses of folic acid alone, the anemia that B12 deficiency causes gets corrected, which makes the deficiency harder to spot while nerve damage continues (textbook knowledge).
Enhancers in food
Fat-soluble vitamins with any food that contains fatCurcumin with fat and black pepperLycopene with fat (tomato scrambled with egg is the classic)

Mechanism · Why long-term zinc needs copper

Zinc makes the cells of the gut wall produce more metallothionein, a protein that binds copper even more tightly than zinc. So during long-term zinc supplementation it traps the copper from food as well, and that copper is shed with the gut cells rather than absorbed.

Short-term zinc (a few weeks) is mostly fine; long-term, high-dose zinc can cause copper deficiency, which shows up as anemia, a low white cell count and nerve damage. The US tolerable upper intake level for zinc (40 mg a day for adults) is set on exactly that effect on copper (NIH ODS).

In practice: if you take zinc long-term (for acne or immune support, say), ask a doctor whether to add a little copper, or have ceruloplasmin (a lab value that reflects the body's copper level) checked regularly.

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Evidence · How tea and coffee block iron

The tannins (a family of polyphenols) in tea and coffee bind non-heme iron into insoluble complexes, so the iron cannot be absorbed. Compared with the same meal taken with water, a cup of black tea with the meal can lower non-heme iron absorption from that meal by 79–94% (Hurrell 1999; the earlier Disler 1975 also saw tea inhibit iron absorption).

Note: this affects only non-heme iron (the iron in plants and iron supplements), not heme iron (the iron in meat). So tea with a steak is fine; tea with spinach, tofu and an iron tablet does make a difference.

In practice: no tea or coffee within 2 hours either side of an iron tablet, and a glass of orange juice (vitamin C) with it works best.

Chapter 3

Dose & form cheat sheet

This is the chapter people consult most: the usual doses, the better forms and the points to watch for common supplements. The doses come from the US National Institutes of Health Office of Dietary Supplements (NIH ODS), the position stands of the International Society of Sports Nutrition (ISSN), and the trials cited in each supplement's own story.

A few general rules for choosing a form:
Minerals: chelated forms (glycinate, citrate, picolinate) usually absorb better and upset the stomach less than inorganic salts (oxide, sulfate).Vitamins: for most vitamins, natural versus synthetic makes little difference. For vitamin D, choose rather than D2. Methylfolate is often said to be better for people with gene variants; the evidence for this is limited.Herbs: look for standardized extracts (such as KSM-66 or Sensoril) rather than just whole-herb powder.
Also keep two kinds of numbers apart: the recommended amount that prevents deficiency, and the dose trials use as treatment. Without a deficiency, you should not take a treatment dose long-term.

In practice · Doses and forms of common supplements

Supplement	Usual dose	Better form	Key caution
Creatine	3–5 g/day	Monohydrate (Creapure)	No loading phase needed; any time of day; safe for people with normal kidney function
Vitamin D3	1000–4000 IU/day	D3 (cholecalciferol)	With a fatty meal; a 25(OH)D of ≥ 50 nmol/L is enough for most people (NIH ODS)
Magnesium	200–400 mg/day	Glycinate, citrate	Supplemental magnesium above 350 mg/day exceeds the tolerable upper intake level (UL) and should be used under medical guidance; oxide is poorly absorbed; caution with kidney impairment
Fish oil EPA+DHA	1–3 g/day	Triglyceride form (TG) is often considered better than ethyl ester (EE); IFOS certified	Read the actual EPA+DHA on the label, not the total weight
Coenzyme Q10	100–200 mg/day	Reduced form (ubiquinol)	With a fatty meal; worth considering for people on statins
Iron (treatment)	60–120 mg every other day	Ferrous sulfate, ferrous bisglycinate	Empty stomach plus vitamin C; alternate days absorb better than daily
Zinc	8–25 mg/day	Picolinate, glycinate	With meals if it causes nausea; add copper for long-term use
Calcium	500–1000 mg/day	Citrate (can be taken on an empty stomach)	≤ 500 mg per dose; keep apart from iron
Vitamin C	100–500 mg/day	Ascorbic acid	Split doses; over 1 g may cause diarrhea
B vitamins	At the RDA	Methyl B12, methylfolate	Vegans must take B12; people on long-term metformin should have B12 checked
Beta-alanine	3.2–6.4 g/day	Plain powder is fine	Split into 0.8–1.6 g doses; the tingling is harmless
Curcumin	500–1500 mg/day	C3 Complex with piperine	With meals; caution with bile duct obstruction or anticoagulants
Ashwagandha	300–600 mg/day	KSM-66 (5% withanolides)	In the evening; know the red flags of liver injury; not in pregnancy
Melatonin	0.3–1 mg	Sublingual or immediate-release	30–60 minutes before bed; more is not better
Glycine	3 g at bedtime	Glycine powder	Cheap and safe; better self-rated sleep quality in small trials
NAC	600–1200 mg/day	NAC capsules	For an acetaminophen (paracetamol) overdose, hospitals use it as the antidote; capsules at home cannot replace the emergency department; caution with G6PD deficiency
HMB	3 g/day	HMB-Ca or HMB-FA	Split doses; very little benefit for young people, small-trial signals in older adults and people on bed rest
TMG (betaine)	1.5–3 g/day	Anhydrous betaine	For people with high homocysteine; take B12 and folate as well

Abbreviations in the table: and are the two omega-3 fatty acids in fish oil; is the Recommended Dietary Allowance (mostly US figures); is the tolerable upper intake level; is N-acetylcysteine; is a breakdown product of leucine; G6PD deficiency is the inherited condition also known as favism.

Evidence · Recommended amounts versus treatment doses

Keep a few concepts apart when you read the numbers in the table:

Recommended Dietary Allowance (): the amount that prevents deficiency disease. For example, the US RDA of vitamin C for adult men is 90 mg, which is set to prevent scurvy. Some argue that higher doses bring extra benefits for immunity and iron absorption; the evidence for this is limited.

Treatment or functional doses: the amounts trials use to reach a specific effect, for example:
Vitamin D deficiency: a loading phase and then maintenance, with the doses set by a doctor from your lab results.Iron deficiency: taking iron every other day gives more total absorption than taking it daily (Stoffel 2017); the dose and length are set by a doctor from your labs.High : check B12 and folate first; in healthy volunteers, a few grams a day of betaine () lowers fasting homocysteine, by about 20% at most at 6 g a day, but it may worsen blood lipids (Olthof 2005).As an add-on for depression: curcumin has only small trials behind it (such as Lopresti 2014), with no agreed dose or form.
Tolerable upper intake level (): above this, taken long-term, risk starts to rise. The US figures, for example: 4000 a day for vitamin D, 45 mg a day for iron (food plus supplements), and 40 mg a day for zinc.

The principle: without a deficiency, do not use treatment doses. Supplementing within the recommended range is insurance; a treatment dose is an intervention and should have a reason and monitoring.

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Chapter 4

Risky supplement and drug combinations

If you take prescription drugs, you need to know these before adding supplements. Some combinations only lower absorption; others can be clinically dangerous. For a more systematic treatment see Drug–Nutrient Interactions; this is the quick reference.

Warfarin (an oral anticoagulant)
Vitamin K: keep your intake steady and do not suddenly eat much more or much less, because vitamin K changes warfarin's anticoagulant effect.Vitamin E, fish oil and ginkgo: raise the risk of bleeding.St John's wort: speeds up the breakdown of warfarin and weakens its effect.Cranberry juice: may strengthen warfarin's effect (case reports).
Blood-pressure drugs and diuretics
Potassium: a potassium-sparing diuretic (spironolactone) plus an ACE inhibitor or blood-pressure drug, plus a potassium supplement, carries a risk of high blood potassium (hyperkalemia).Magnesium: thiazide and loop diuretics increase magnesium loss in the urine.Licorice (glycyrrhizin): weakens blood-pressure drugs and causes low potassium.
Antidepressants (, )
St John's wort: risk of serotonin syndrome ( syndrome, an emergency caused by too much serotonin); never combine it with an SSRI.5-hydroxytryptophan (): the same risk.: in theory raises the risk of serotonin syndrome.
Two more groups: combinations involving statins, contraceptives, and iron with antibiotics; and combinations such as levothyroxine, metformin and proton pump inhibitors that only lower absorption slowly.

Safety · Statins, contraceptives and iron

Statins (simvastatin, atorvastatin and others)
Coenzyme : statins block a key enzyme of cholesterol synthesis (HMG-CoA reductase) and in doing so also reduce the body's CoQ10 production. But show that taking CoQ10 does not reliably relieve muscle pain.Grapefruit juice: blocks the gut-wall enzyme () that breaks down some statins, such as simvastatin, raising their blood levels and the risk of muscle damage.Red yeast rice: contains monacolin K, which is lovastatin; taking it with a statin amounts to a double dose, with a risk of muscle damage.
Contraceptives and hormones
St John's wort: speeds up estrogen breakdown and may make contraception fail.Folate: contraceptives may lower folate levels, so take it before trying to conceive.
Iron and other drugs
Tetracycline and quinolone antibiotics: they bind iron and both are absorbed less; keep them 2–4 hours apart.Levothyroxine: iron binds it in the gut; keep them 4 hours apart.Levodopa: iron lowers its absorption.

In practice · Combinations that only lower absorption

These three are not acute dangers. They are the slow drift of a nutrient or drug level over months of use, and keeping doses apart plus regular rechecks keeps them in hand.

Levothyroxine
Calcium, iron, aluminum and magnesium bind levothyroxine in the gut and reduce its absorption; keep them 4 hours apart.Coffee clearly reduces its absorption.Food: take the tablet on an empty stomach and wait 30–60 minutes before eating.Soy and high-fiber foods may reduce absorption.
Metformin
Vitamin B12: low B12 becomes more common after long-term use (>4 years). In DPPOS at 5 years, B12 deficiency (≤ 203 pg/mL) was 4.3% versus 2.3% in the placebo group, and deficiency plus borderline-low levels together were 19.1% versus 9.5%. Have B12 checked regularly and supplement when needed.Folate: metformin may also affect folate levels.
Proton pump inhibitors (, acid-suppressing drugs such as omeprazole)
Vitamin B12: stomach acid helps release B12 from food proteins, so long-term PPI use raises the risk of B12 deficiency.Magnesium: the US Food and Drug Administration (FDA) has warned that long-term PPI use can cause low magnesium.Calcium and iron: stomach acid helps absorb them, and long-term PPI use may affect both.

In practice · What to stop 2 weeks before surgery

If you are having surgery, the anesthetist will usually ask you to stop supplements that raise bleeding risk or interact with anesthetic drugs:

Stop 2 weeks before: fish oil (high-dose and ), vitamin E (>400 ), ginkgo, allicin (high-dose garlic extract), ginger (high doses), danshen, dong quai and other herbs used to promote blood flow.

Stop 1 week before: St John's wort (it affects how several anesthetic drugs are broken down).

No need to stop: vitamin D, B vitamins, magnesium, calcium (unless your doctor says otherwise) and creatine.

You must tell the anesthetist: every supplement you take, including the natural ones.

Chapter 5

What athletes should buy first

More supplements are not better. Rank them by your goal and spend on the things with the strongest evidence; sports nutrition experts commonly sort training supplements into tiers by strength of evidence.

Tier 1: the foundation (almost everyone)
Creatine, 3–5 g a day: multiple randomized trials agree, so the certainty of evidence is high; used for muscle gain, strength and recovery.Vitamin D: if you get little sun, or your is <50 nmol/L.Omega-3 (fish oil): if you eat fatty fish fewer than 2–3 times a week.Protein: 1.6–2.2 g/kg a day (food first, with protein powder if food falls short).
Not recommended (weak evidence or negative results)
Branched-chain amino acids (): no use once your protein intake is adequate.Glutamine: no extra benefit for healthy people who train.Testosterone boosters (tongkat ali, fenugreek and the like): weak evidence.L-carnitine: does not work for fat loss.Most fat burners: the only ingredient that does anything is often the caffeine.
The order to follow: get training, nutrition and sleep right first, then consider Tier 1. Once Tier 1 is in place, consider Tier 2, chosen by goal. Tier 3 is the icing. Skipping the foundation to buy Tier 3 is the most common waste.

In practice · Choosing from Tiers 2 and 3

Tier 2: chosen by goal
Strength and muscle gain: creatine (Tier 1) plus caffeine (3–6 mg per kg of body weight before training), then Beta-alanine (if you train at high intensity for 1–4 minutes) and (if you are cutting or are an older adult).Endurance: caffeine plus electrolytes (sodium, potassium, magnesium) plus carbohydrate (carbohydrate is nutrition, not a supplement); Beta-alanine for events lasting 1–4 minutes.Fat loss: caffeine plus protein (to stay full); note that most so-called fat-loss supplements have weak evidence.Recovery: creatine, protein, and sleep (sleep is not a supplement, but it matters most); tart cherry juice has weak evidence.
Tier 3: marginal or early evidence
Citrulline, 6–8 g a dose: for the pump and blood flow; the certainty of evidence is low, with only a few small crossover trials. (betaine), 2.5 g a day: a small difference in strength; the certainty of evidence is low.Taurine, 1–6 g a day: fluid balance in cells and performance; early evidence only.Ashwagandha: worth considering when stress is high or sleep is poor.

Evidence · The priority order for training supplements

The order below is this story's own summary, drawn from the evidence for each supplement, including the International Society of Sports Nutrition (ISSN) position stands on individual supplements: creatine (Kreider 2017), Beta-alanine (Trexler 2015) and (Wilson 2013). It is not a single ranking issued by any one document. Certainty of evidence is given in four levels: high, moderate, low and very low.

1. A training plan plus enough protein: the foundation.
2. Creatine, 5 g a day: high (multiple randomized trials agree; almost every training population).
3. Caffeine: high (multiple randomized trials; an acute effect).
4. Beta-alanine: moderate (randomized trials, mainly for high intensity lasting 1–4 minutes).
5. HMB, 3 g a day: low to moderate (small randomized trials; cutting, older adults, bed rest).
6. Citrulline: low (a few small crossover trials; pump and blood flow).
7. (betaine), 2.5 g a day: low (small trials; a small difference in strength).
8. Everything else: low or very low.

The core logic of the order: pull the big levers first, then fill the small gaps. For most people, the first three items already capture most of what supplements can offer.

Chapter 6

Pregnancy, children, chronic illness

General advice does not apply to everyone. For the groups below, supplement choices need extra care: some things are a must, others are strictly off-limits.

Pregnancy or trying to conceive
Avoid: vitamin A (the retinol form above 10,000 a day can cause birth defects); ashwagandha; red yeast rice; high-dose caffeine (>200 mg/day); St John's wort; most herbal products.Note: choose a low-mercury fish oil, and do not take cod liver oil (too much vitamin A).
Children and teenagers
Avoid: adult-dose supplements; melatonin (unless a doctor directs it); creatine (data in teenagers are limited, though the ISSN considers it safe for under-18s under supervision).Note: iron supplements are one of the most common causes of acute poisoning in children. The dose falls into three bands: < 20 mg/kg elemental iron is usually non-toxic, 20–60 mg/kg is mild-to-moderate poisoning, and > 60 mg/kg can be fatal. At 40 mg/kg or more, or once there are clear symptoms, the child must be taken to hospital. If you suspect a child has swallowed iron tablets, do not wait at home for symptoms: contact poison control or go to the emergency department now. Keep them stored out of reach and locked away.
Remember: supplements are not safe just because they are natural. They are pharmacologically active and, like drugs, have side effects and interactions. If you have a chronic condition or take medication, tell your doctor or pharmacist before adding any supplement.

In practice · What each group should take

Pregnancy or trying to conceive
Must take: folic acid 400–800 mcg a day (from 1 month before conception to 12 weeks of pregnancy, to prevent neural tube defects); vitamin D 600 a day (the US Recommended Dietary Allowance); iron (if screening shows a deficiency); 200–300 mg a day.
Breastfeeding
Continue folate, vitamin D and iron (if deficient); DHA passes to the baby through breast milk.Limit caffeine (<300 mg/day, and watch whether the baby is fussy).Avoid herbs (ashwagandha, St John's wort and others).
Children and teenagers
Vitamin D 400 IU a day (the American Academy of Pediatrics, AAP, recommendation, starting from birth).Iron: for exclusively breastfed babies, pay attention to iron sources from 4–6 months, earlier for premature babies, and follow the pediatrician.
People taking anticoagulants or antiplatelet drugs: see the chapter Risky supplement and drug combinations in this story.

Older adults (65 and over)
Vitamin D (supplement if deficient; linked to fall prevention); B12 (absorption declines, so check it regularly); calcium (if diet falls short); magnesium.Creatine 3–5 g a day (studied for sarcopenia, strength and cognition). 3 g a day (to preserve muscle during bed rest or after surgery; supported by small randomized trials).Protein (PROT-AGE recommendations): 1.0–1.2 g/kg/day if healthy, at least 1.2 g/kg/day with regular exercise, and 1.2–1.5 g/kg/day with an acute or chronic illness. Older adults need more than younger ones because of anabolic resistance: the same protein triggers a weaker muscle-building response in older muscle. People with chronic kidney disease who are not yet on dialysis are the exception and follow the amount their kidney doctor sets.Note: when taking several medicines at once, check for interactions between drugs and supplements.

Safety · Cautions for chronic conditions

With a chronic disease, the risk is not whether you take supplements but whether a supplement collides with a drug you already take, or adds load to an organ that is already struggling.

Chronic kidney disease: avoid high-protein, high-potassium, high-magnesium and high-phosphorus supplements; vitamin D needs a doctor's monitoring.Liver disease: avoid red yeast rice, kava and high-dose niacin; ashwagandha has case reports of liver injury.Diabetes: chromium, alpha-lipoic acid and cinnamon may strengthen glucose-lowering drugs, so watch for low blood sugar; berberine's mechanism overlaps with metformin's.Autoimmune disease: avoid supplements that stimulate the immune system (echinacea, beta-glucans, high-dose zinc); ashwagandha carries a theoretical risk.Gout: avoid high-dose niacin (>1 g/day); vitamin C may lower uric acid slightly, but the evidence is inconsistent.

Background · This is not medical advice

This story is education to help you understand the principles of using supplements; it is not medical advice.

The doses come from published research and guidelines from authoritative bodies, but the right dose for you depends on your age, weight, health, diet, medicines and genes.If you have any illness, take any medicine, or are pregnant, breastfeeding or trying to conceive, you must talk with a doctor or registered dietitian before adding supplements.Supplements cannot replace a balanced diet, regular exercise, enough sleep and necessary medical care.If a supplement claims to cure everything, to be natural with no side effects or to work instantly, it is most likely marketing.Tell your doctor about any adverse reaction; you can also report it through FDA MedWatch in the US or China's National Medical Products Administration (NMPA).
Where this story starts from: know what to do, and know why. Understanding the mechanism matters more than memorizing doses, and knowing when not to supplement matters more than knowing what to take.

References · 13

Kreider, R. B., et al. (2017). International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 14, 18. Position stand: short- and long-term creatine supplementation, up to 30 g/day for 5 years, is safe and well tolerated in healthy individuals and in a number of patient populations from infants to the elderly; the stand adds that significant health benefits may come from ensuring a habitual low-dose creatine intake (e.g., 3 g/day) throughout the lifespan (abstract, PMID 28615996). 10.1186/s12970-017-0173-z
Trexler, E. T., Smith-Ryan, A. E., Stout, J. R., et al. (2015). International society of sports nutrition position stand: Beta-Alanine. Journal of the International Society of Sports Nutrition, 12, 30. 10.1186/s12970-015-0090-y
US Preventive Services Task Force. (2022). Vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer: recommendation statement. JAMA, 327(23), 2326–2333. 10.1001/jama.2022.8970
Hurrell, R. F., Reddy, M., & Cook, J. D. (1999). Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. British Journal of Nutrition, 81(4), 289-295. Black tea reduced non-heme iron absorption 79-94% vs a water-control bread meal; peppermint 84%, cocoa 71%, camomile 47%. Dose-dependent with total polyphenols. Green tea was not tested. 10.1017/S0007114599000537
Hewlings, S. J., & Kalman, D. S. (2017). Curcumin: a review of its effects on human health. Foods, 6(10), 92. 10.3390/foods6100092
Shoba, G., et al. (1998). Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers. Planta Medica, 64(4), 353–356. Pharmacokinetic study, not a clinical-outcome trial (kind changed from rct to mechanism on 2026-09-24). Rats: curcumin 2 g/kg with piperine 20 mg/kg raised bioavailability by 154%. Healthy human volunteers: 2 g curcumin alone gave undetectable or very low serum levels; adding 20 mg piperine produced much higher concentrations from 0.25 to 1 h after the dose, a 2000% increase in bioavailability, with no adverse effects. The abstract gives neither the number of volunteers nor whether the human comparison was randomized (abstract, PMID 9619120). 10.1055/s-2006-957450
Prescott, L. F., Park, J., Ballantyne, A., Adriaenssens, P., & Proudfoot, A. T. (1977). Treatment of paracetamol (acetaminophen) poisoning with N-acetylcysteine. The Lancet, 2(8035), 432-434. 15 patients with paracetamol poisoning given IV N-acetylcysteine 300 mg/kg over 20 h, with no control group: liver-function tests stayed normal or only slightly disturbed in 11 of the 12 treated within 10 h; severe liver damage developed in the other one and in all 3 treated more than 10 h after ingestion (abstract, PMID 70646). 10.1016/S0140-6736(77)90612-2
Olthof, M. R., van Vliet, T., Boelsma, E., & Verhoef, P. (2003). Low dose betaine supplementation leads to immediate and long term lowering of plasma homocysteine in healthy men and women. The Journal of Nutrition, 133(12), 4135-4138. 10.1093/jn/133.12.4135
Wilson, J. M., Fitschen, P. J., Campbell, B., et al. (2013). International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB). Journal of the International Society of Sports Nutrition, 10, 6. Position points: HMB can enhance recovery by attenuating exercise-induced muscle damage; take it close to the workout, ideally for 2 weeks before an exercise bout; 38 mg/kg body mass daily; HMB-FA may raise plasma HMB more than HMB-Ca, but research is too limited to say one form is superior; chronic use is safe. The text puts dietary sources in perspective: over 600 g of protein would be needed to supply the 60 g of leucine that yields the typical 3 g/day HMB dose. Equivalent doses of HMB-FA (0.8 g) vs HMB-Ca (1.0 g) gave double the peak plasma level in a quarter of the time (30 vs 120 min); suggested timing 30-60 min before exercise for HMB-FA and 60-120 min for HMB-Ca. Its two tables summarise HMB studies only; there is no table ranking supplements. Several authors report industry funding (abstract, PMID 23374455; full text, PMC3568064). 10.1186/1550-2783-10-6
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