When to Take Supplements: A Sourced Chart

Quick answer

Official sources give timing notes for some supplements, not one schedule. Calcium is absorbed best in amounts of 500 mg or less at a time, iron and calcium can interfere with each other, vitamin D is absorbed better with fat, and the levothyroxine label lists calcium and iron among products that can lower its absorption.^1,2,3,4

Key facts

NIH says calcium is absorbed best in amounts of 500 mg or less at one time, and that carbonate is absorbed best with food.¹
Experts suggest taking individual calcium and iron supplements at different times of the day, although the interference has not been definitively established.²
Coffee taken with an iron dose cut absorption by 54% in one study, and a breakfast with coffee and orange juice cut it by 66%.⁵
A single 200 mg dose of vitamin C was fully absorbed in one study, while single doses of 500 mg or more were absorbed less completely.⁶
Most of these notes concern food, amounts or spacing; the one clock-time result we found, for iron, just missed statistical significance.⁵
The levothyroxine label lists calcium carbonate and iron among products to keep apart from the medicine, so spacing is a question for a pharmacist.^4,7

When to take supplements: a chart of what the sources say

There is no official schedule that covers supplements as a group. The chart gathers the timing notes we found, with the kind of source beside each, so you can see which are fact-sheet statements and which are single studies.^1,2

Timing notes by supplement^{1,2,3,5,6,8,9,10,11,12,13,14,15,16,17,18,19}
Supplement	What the sources say about timing	Kind of source
Calcium	Absorbed best in amounts of 500 mg or less at one time; carbonate with food, citrate with or without	NIH fact sheet
Iron	High doses on an empty stomach are the most likely to upset it; calcium and iron are best taken at different times; coffee with a dose cut absorption by 54%	NIH fact sheet and one study
Zinc	Iron at 25 mg or more taken at the same time can lower zinc absorption	NIH fact sheet
Magnesium	The share absorbed is higher when taken in several small amounts than in one large amount	One study
Vitamin D	Absorbed better with a meal or snack that includes some fat	NIH fact sheet
Vitamin B12	The absorbing protein saturates at about 1.5 to 2 mcg per meal, so the share absorbed falls as the amount rises	NIH fact sheet and a review
Vitamin C	A single 200 mg dose was fully absorbed, while 500 mg or more was absorbed less completely; vitamin C at the same meal helps absorption of plant iron	One controlled study and an NIH fact sheet
Folic acid	About 85% absorbed with food, nearly 100% without	NIH fact sheet
Omega-3 fish oil	Absorption of EPA from ordinary fish oil rose from 69% to 90% with a high-fat meal	One study
Probiotics	Bacteria survived best with a meal or 30 minutes before one in a laboratory model, not in people	Laboratory model
Protein	The ISSN suggests spreading protein across the day in servings every 3 to 4 hours; a meta-analysis found no significant extra strength or size from protein within an hour of exercise	Position stand and meta-analysis
Creatine	Trials that gave it just before or just after training found similar results	Randomized trials

What time of day do studies point to?

Time of day is rarely tested. Most notes in the chart concern food, amounts or spacing between products, not the clock.^5,9

In a study of 34 women with low iron stores, a 100 mg dose taken in the afternoon was absorbed 37% less than the same dose taken in the morning, a difference that just missed statistical significance.⁵

That iron result missed statistical significance, so it is a hint, not a rule. Beyond it, the sources we read leave morning or evening to routine, which makes the label's directions and a pharmacist the tie-breakers.⁵

When to take supplements for best absorption

Three ideas explain most of the chart, and each has its own source.^1,2

Fat in the meal helps fat-soluble nutrients such as vitamin D, vitamin E and omega-3 fats, with fat-soluble vitamin K absorbed like dietary fat.^3,14,20,21
The share absorbed falls as a single amount rises for calcium, vitamin B12, magnesium and vitamin C, which is why NIH suggests smaller amounts for calcium.^1,6,11,22
Some minerals compete: iron at 25 mg or more with zinc, and calcium with iron. Our guide to taking several supplements at once covers pairs.^2,8

Eating foods that contain vitamin C at the same meal as plant sources of iron helps the body absorb more of that iron.^12,23

When to take supplements when intermittent fasting

No source we read tested supplement timing around fasting windows, so there is no finding to report either way. What the sources do say can be read against an eating window: fat-soluble vitamins are absorbed better with a meal that contains fat, calcium carbonate is absorbed best with food, high doses of iron may upset an empty stomach, and folic acid is absorbed more fully without food.^1,3,13,24

Those are notes about food, not about fasting, and the gap is not a finding either way. A pharmacist or registered dietitian is the person to ask how your products fit your eating pattern.²⁵

When to take supplements after levothyroxine

Levothyroxine is a prescription thyroid medicine. Its label lists calcium carbonate and iron among products that can lower how much of the medicine is absorbed. How far apart to take them depends on the medicine, the product and you, so it is a question for the prescriber or pharmacist, who can set a schedule against your own label.^4,7

Ask your pharmacist how far apart to take them

Calcium carbonate can bind levothyroxine in the gut and reduce how much is absorbed. The levothyroxine label lists calcium carbonate among products to keep apart from the medicine, and a small study found calcium citrate and acetate had a similar effect; ask your pharmacist how to space them.^1,4,26,27,28

On the medicine's label

Ask your pharmacist how far apart to take them

Iron supplements can reduce how much levothyroxine the body absorbs and make it less effective. The levothyroxine label lists ferrous sulfate among products that may bind the medicine and says to take them apart; ask your pharmacist how to space them.^2,7,24,29

On the medicine's label

Ask your pharmacist how far apart to take them

Calcium and iron can reduce how much levothyroxine is absorbed. The levothyroxine label tells patients that iron and calcium supplements can decrease its absorption, and MedlinePlus names calcium carbonate and iron supplements, and also niacin, among products that may interact with it. Many multivitamins contain calcium, and some contain iron.^30,31,32,33

On the medicine's label

The same pattern appears with some antibiotics, and our pages on those medicines and on levothyroxine list the supplements that official sources name for each.^34,35

Questions people ask

When to take supplements and vitamins?

There is no single schedule. NIH and studies give notes for specific supplements, such as fat with vitamin D, food with calcium carbonate, and calcium and iron at different times.^1,2,3

When to take supplements during the day?

Studies rarely tested a clock time. One study found a 100 mg iron dose absorbed 37% less in the afternoon than in the morning, a difference that just missed significance.⁵

When to take supplements for best absorption?

NIH ties absorption to food, amount and spacing: fat helps vitamin D, calcium is absorbed best at 500 mg or less at a time, and iron may interfere with zinc and calcium.^1,3,8

When to take supplements after levothyroxine?

Ask your pharmacist or doctor. The levothyroxine label lists calcium carbonate and iron among products that can lower its absorption, and spacing is set against your own prescription.^4,7

When to take supplements when intermittent fasting?

No source we read tested this. The food notes in the chart can be read against an eating window, but a pharmacist or dietitian is the person to ask.^1,3

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.