Why the timing matters at all

Most supplements are swallowed together, with breakfast, because that is when people remember. For the water-soluble vitamins it makes little difference. For the minerals it does.

Iron, calcium, zinc and magnesium compete for the same routes through the gut wall. Take them together and each gets in less well. The effect is large for iron. In Hallberg’s studies, calcium in the same meal cut the iron absorbed by around half.1 Tea did worse: in Morck’s work it cut iron absorption from a meal by nearly two thirds, and coffee by about 40%.2

The fat-soluble ones have the opposite problem. Vitamin D and fish oil need fat in the gut to be absorbed. When patients taking vitamin D moved it from an empty stomach to their largest meal, their blood levels rose by about half, with no change in dose.5

So the same bottle can do quite different amounts of good depending on when you open it. I see this most with iron: patients whose levels will not rise, taking their tablet with a cup of tea and a calcium pill.

How the map places each supplement

The day has four slots: morning on an empty stomach, the midday meal, late afternoon, and bedtime. Each is at least four hours from the next, which covers every separation below. Each supplement has a preferred slot and a fallback, and the map picks the arrangement that keeps every competing pair apart while moving as few things as possible from where they work best.

  • Iron: morning, before breakfast, with vitamin C or orange juice. Late afternoon, between meals, if the morning is taken.3,4
  • Vitamin D and fish oil: with the midday meal, assuming it has some fat in it. If your largest meal is dinner, take them then.
  • Calcium: with a meal, away from iron and zinc. Carbonate needs food; citrate does not. You absorb it best 500 mg or less at a time.7
  • Zinc: late afternoon, with a light snack. On an empty stomach it often brings on nausea.
  • Magnesium: bedtime, where it is out of everyone else’s way.
  • B-complex: with the midday meal. Some people sleep worse when they take it late.
  • Probiotics: with or just before breakfast, unless the label says otherwise.11

Where there are too many competing minerals for four slots, the map says so, and marks the card that has to share. That happens most often with levothyroxine, which takes the morning for itself.

Prescriptions worth checking against your supplements

I kept this list short on purpose. These are the eleven where the interaction is well documented, common, and changes what you should do. They are not scheduled themselves, because your prescriber has already decided when you take them. Some move the supplements around them, and some simply come with a warning.

  • Levothyroxine (Synthroid, Levoxyl) takes the morning alone. Iron, calcium and magnesium go at least four hours later.6,10
  • Bisphosphonates (Fosamax, Actonel, Boniva) need an empty stomach and plain water, then 30 minutes with nothing else, 60 for Boniva. Most are weekly or monthly, so this changes one morning.
  • Quinolone and tetracycline antibiotics (Cipro, Levaquin, doxycycline) are bound by iron, calcium, magnesium and zinc in the gut. Separate them by 2 hours before or 6 hours after.
  • Acid reducers (Prilosec, Nexium, Pepcid) lower the stomach acid that iron and calcium carbonate need. Used for years, PPIs can also lower magnesium and B12.8,9
  • Warfarin (Coumadin, Jantoven) does not change the schedule, but any change in what you take should go past your anticoagulation clinic first.
  • Thiazide diuretics (Microzide, and combination pills such as Hyzaar and Zestoretic) make the kidneys hold on to calcium. Add calcium and vitamin D, and the blood level is worth checking.
  • Statins (Lipitor, Zocor, Crestor, Pravachol) need no change to the schedule. Red yeast rice is the supplement to avoid, since it contains a natural statin.12 High-dose niacin adds to the risk of muscle injury,13 and St John’s wort lowers simvastatin levels.14 Simvastatin has a lower dose ceiling when taken with amlodipine, diltiazem or verapamil.16 Large amounts of grapefruit juice raise simvastatin and atorvastatin levels.15
  • Beta-blockers (Lopressor, Toprol, Tenormin, Coreg): calcium and aluminum or magnesium antacids can lower how much atenolol or propranolol is absorbed, so keep them 2 hours apart.18 Stopping one suddenly raises the risk of a heart event.17
  • ACE inhibitors and ARBs (Zestril, Vasotec, Cozaar, Diovan) raise blood potassium. Potassium supplements and potassium-based salt substitutes can push it too high.19
  • Calcium channel blockers (Norvasc, Cardizem, Calan, Procardia): St John’s wort can lower the level of verapamil, and probably of others in the class.20

If you take something that is not on the list, that does not mean it is safe with your supplements. It means it is a question for your pharmacist and/or primary care provider, who can see everything you take at once.

What this cannot tell you

It cannot tell you whether you need any of these. That is the more important question, and most people skip it. Iron in particular is for a deficiency shown on a blood test. In the large cohort studies I wrote about in my supplements article, iron was the supplement that looked worst. Taken without a reason, it is not a neutral act.

It also does not know your doses, the form of each product, or whether you have kidney disease, which changes the rules for magnesium and calcium entirely. If you do, take this schedule to your own doctor rather than following it.

If you are not sure whether your diet is short of something, the nutrient gap finder is a better first step than any bottle.

Questions people ask about this

What is the best time to take iron?

On an empty stomach, 30 to 60 minutes before breakfast, with water or a small glass of orange juice, and with no coffee, tea or milk from an hour before to two hours after. If that makes you sick, take it with a light meal without dairy. You absorb less, but more than from tablets you stop taking. Taking it every other day rather than daily can also mean more iron absorbed per tablet.

Can I take calcium and iron together?

No. Calcium in the same dose can cut the iron you absorb by half or more. Keep them at least four hours apart: iron in the morning before breakfast, and calcium with lunch or later in the day works for most people.

Should I take vitamin D in the morning or at night?

The clock matters less than the meal. Vitamin D is fat-soluble, and taking it with the largest meal of the day, one with some fat in it, raised blood levels by about half in one study. For most people that is lunch or dinner.

When is the best time to take magnesium?

Bedtime suits most people, and it keeps magnesium away from iron, zinc and calcium earlier in the day. Citrate and oxide loosen the stools; glycinate is gentler. Above 350 mg a day from supplements, diarrhea is the usual first sign of too much.

Can I take my supplements with levothyroxine?

Not at the same time. Levothyroxine goes first, alone, with water, 30 to 60 minutes before breakfast. Iron, calcium and magnesium need to be at least four hours later, because they bind the hormone in the gut and lower the dose you absorb. Coffee taken with it lowers absorption too.

Do I need to separate supplements from antibiotics?

For quinolones such as Cipro and Levaquin, and tetracyclines such as doxycycline, yes. Take each dose at least 2 hours before or 6 hours after iron, calcium, magnesium or zinc, which bind the antibiotic and can stop it working. For a short course it is often simplest to pause those supplements, with your prescriber’s agreement.

Is it fine to take all my vitamins at once?

For many combinations, yes. The water-soluble vitamins and fish oil rarely clash with anything. The problems come from the minerals (iron, calcium, zinc and magnesium) competing with each other, and from a few prescriptions that minerals bind to. Separate those and the rest can share a meal.

References

  1. Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hultén L. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 1991;53(1):112–119. doi:10.1093/ajcn/53.1.112 Calcium in the same meal roughly halves iron absorption: the reason iron and calcium are never in one slot.
  2. Morck TA, Lynch SR, Cook JD. Inhibition of food iron absorption by coffee. Am J Clin Nutr. 1983;37(3):416–420. doi:10.1093/ajcn/37.3.416 Coffee and tea with a meal reduce iron absorption; the source of the no-coffee, no-tea window.
  3. Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematol. 2017;4(11):e524–e533. doi:10.1016/S2352-3026(17)30182-5 Alternate-day morning dosing absorbs more iron per dose than daily dosing.
  4. Li N, Zhao G, Wu W, et al. The efficacy and safety of vitamin C for iron supplementation in adult patients with iron deficiency anemia: a randomized clinical trial. JAMA Netw Open. 2020;3(11):e2023644. doi:10.1001/jamanetworkopen.2020.23644 Adding vitamin C to iron tablets made little difference to recovery: why the map pairs them without promising much.
  5. Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 2010;25(4):928–930. doi:10.1002/jbmr.67 Moving the same dose of vitamin D to the largest meal raised blood levels by about half.
  6. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12):1670–1751. doi:10.1089/thy.2014.0028 Separating levothyroxine from iron and calcium by about four hours.
  7. National Institutes of Health, Office of Dietary Supplements. Calcium: fact sheet for health professionals. ods.od.nih.gov Carbonate versus citrate, and absorption falling above 500 mg per dose.
  8. US Food and Drug Administration. FDA Drug Safety Communication: low magnesium levels can be associated with long-term use of proton pump inhibitor drugs (PPIs). 2011. The basis for the long-term PPI and magnesium note.
  9. Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435–2442. doi:10.1001/jama.2013.280490 Two or more years of acid suppression and B12 deficiency.
  10. Benvenga S, Bartolone L, Pappalardo MA, et al. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid. 2008;18(3):293–301. doi:10.1089/thy.2007.0222 Coffee taken with levothyroxine lowers its absorption.
  11. Tompkins TA, Mainville I, Arcand Y. The impact of meals on a probiotic during transit through a model of the human upper gastrointestinal tract. Benef Microbes. 2011;2(4):295–303. doi:10.3920/BM2011.0022 Probiotic bacteria survived best when taken with or just before a meal.
  12. Gordon RY, Cooperman T, Obermeyer W, Becker DJ. Marked variability of monacolin levels in commercial red yeast rice products: buyer beware! Arch Intern Med. 2010;170(19):1722–1727. doi:10.1001/archinternmed.2010.382 Red yeast rice contains monacolin K, which is lovastatin, in amounts that vary widely between products.
  13. HPS2-THRIVE Collaborative Group. Effects of extended-release niacin with laropiprant in high-risk patients. N Engl J Med. 2014;371(3):203–212. doi:10.1056/NEJMoa1300955 Niacin added to a statin increased myopathy.
  14. Sugimoto K, Ohmori M, Tsuruoka S, et al. Different effects of St John’s wort on the pharmacokinetics of simvastatin and pravastatin. Clin Pharmacol Ther. 2001;70(6):518–524. St John’s wort lowered simvastatin levels but not pravastatin.
  15. Bailey DG, Dresser G, Arnold JMO. Grapefruit–medication interactions: forbidden fruit or avoidable consequences? CMAJ. 2013;185(4):309–316. doi:10.1503/cmaj.120951 Grapefruit raises simvastatin and atorvastatin levels.
  16. US Food and Drug Administration. FDA Drug Safety Communication: new restrictions, contraindications, and dose limitations for Zocor (simvastatin) to reduce the risk of muscle injury. 2011. Simvastatin dose limits alongside amlodipine, diltiazem and verapamil.
  17. Psaty BM, Koepsell TD, Wagner EH, LoGerfo JP, Inui TS. The relative risk of incident coronary heart disease associated with recently stopping the use of beta-blockers. JAMA. 1990;263(12):1653–1657. Stopping a beta-blocker was followed by more coronary events.
  18. Kirch W, Schäfer-Korting M, Axthelm T, Köhler H, Mutschler E. Interaction of atenolol with furosemide and calcium and aluminum salts. Clin Pharmacol Ther. 1981;30(4):429–435. Calcium and aluminum salts lowered atenolol absorption.
  19. Raebel MA. Hyperkalemia associated with use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. Cardiovasc Ther. 2012;30(3):e156–e166. doi:10.1111/j.1755-5922.2010.00258.x Raised potassium with ACE inhibitors and ARBs.
  20. Tannergren C, Engman H, Knutson L, et al. St John’s wort decreases the bioavailability of R- and S-verapamil through induction of the first-pass metabolism. Clin Pharmacol Ther. 2004;75(4):298–309. St John’s wort lowered verapamil levels.