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Supplement Timing Schedule — When to Take What

Most supplement bottles say take daily — that is not good enough. The time you take your supplements affects how much you actually absorb. Build your personalized daily schedule in 30 seconds based on NIH absorption science.

197+ timing rules
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Example personalized schedule

SAMPLE DAILY SCHEDULE — LEVOTHYROXINE + COMMON SUPPLEMENTS
6:30 AM
Before breakfast
Levothyroxine · Iron
Empty stomach required — food blocks absorption of both. Wait 30-60 min before eating.
7:30 AM
With breakfast
Vitamin D3 · K2 · CoQ10 · Fish Oil
Fat-soluble vitamins absorb best with dietary fat. Morning meal is ideal.
12:30 PM
With lunch
Zinc · B-Complex
With food reduces nausea. 4+ hours from Levothyroxine and Iron.
6:30 PM
With dinner
Calcium · Vitamin C
Calcium separated from Iron by 12 hours. Vitamin C enhances calcium absorption.
10:00 PM
Bedtime
Magnesium Bisglycinate · Melatonin
Magnesium supports GABA — most effective when cortisol drops at night.

Timing facts most people get wrong

Magnesium
Bedtime
Works with GABA system — most effective when cortisol drops at night. Morning magnesium is largely wasted.
Vitamin D3
With largest meal
Fat-soluble — needs dietary fat. Avoid at night as it may suppress melatonin production.
Iron
Empty stomach AM
Absorbs best alone. Separate from calcium, zinc, and coffee by at least 2 hours.
Zinc
With food
Empty stomach causes nausea. Separate from iron and copper by 2+ hours.
Probiotics
Before breakfast
Stomach acid is lowest before meals — bacteria survive transit to intestines better.
CoQ10
With breakfast
Fat-soluble. Ubiquinol form absorbs significantly better than ubiquinone with any meal.
Vitamin K2
With fatty meal
Fat-soluble. MK-7 form stays active in body for 72 hours — daily dosing not strictly required.
Omega-3 Fish Oil
With largest meal
Absorbs significantly better with food. Reduces fishy burps. rTG form absorbs best.

Common timing conflicts to avoid

⛔
Iron + Calcium — never together
Calcium reduces iron absorption by up to 60%. Separate by at least 2 hours. Ideally take iron in the morning and calcium in the evening.
⛔
Zinc + Iron — separate by 2 hours
Both use the same absorption transporter. Taking together reduces absorption of both. Take zinc with dinner and iron in the morning.
⛔
Zinc + Copper — balance required
High dose zinc taken long-term depletes copper. If taking more than 25mg zinc daily, add 1-2mg copper separately.
⚠️
Levothyroxine + Calcium, Iron, Zinc — 4 hour separation
These minerals bind to Levothyroxine in the gut and block absorption of your thyroid medication. Take Levothyroxine on an empty stomach at least 4 hours before any of these.
⚠️
Fat-soluble vitamins without fat
Vitamins D3, K2, A, and E require dietary fat for absorption. Taking them on an empty stomach wastes much of the dose.

How to build your schedule

1
Enter your supplements
Add all your vitamins, minerals, and supplements to Elthio
2
Add your medications
Include prescription medications — some require specific separation times from supplements
3
Set your meal times
Enter your typical wake time, breakfast, lunch, dinner, and bedtime
4
Get your personalized schedule
Elthio generates a complete daily timing schedule based on NIH absorption science and your specific combination

Why timing matters — the science

Supplement timing is not arbitrary. The time you take a supplement affects how much reaches your bloodstream, how it interacts with food and other supplements, and whether it works in sync with your body's natural rhythms.

Magnesium taken at night supports the GABA neurotransmitter system that regulates sleep — the same system that becomes most active when cortisol drops in the evening. The same dose of magnesium taken in the morning has significantly less effect on sleep quality.

Vitamin D3 absorbed with dietary fat reaches levels approximately 32% higher than the same dose taken fasting, according to research published in the Journal of the Academy of Nutrition and Dietetics. For people who are deficient this difference is clinically meaningful.

Iron absorbed on an empty stomach reaches significantly higher serum levels than iron taken with food — but food reduces the nausea that makes iron supplements intolerable for many people. Elthio balances efficacy and tolerability in its recommendations.

Frequently asked questions

When should I take magnesium?
Magnesium bisglycinate or glycinate is best at bedtime — 30 to 60 minutes before sleep. It supports GABA activity which is most effective when cortisol drops at night.
When should I take Vitamin D?
With your largest meal — preferably breakfast or lunch. Vitamin D is fat-soluble and needs dietary fat for absorption. Avoid taking it at night as it may affect melatonin and sleep quality.
Can I take iron and calcium together?
No — they compete for the same absorption pathway. Calcium reduces iron absorption by up to 60%. Separate by at least 2 hours. Take iron on an empty stomach in the morning and calcium with food at a different time.
When should I take zinc?
With food to prevent nausea. Evening with dinner works well. Separate from iron by at least 2 hours as they compete for the same absorption pathway.
When should I take probiotics?
First thing in the morning before breakfast when stomach acid is lowest. This gives bacteria the best chance of surviving transit to the intestines.
Does timing really matter that much?
Yes — significantly. Iron with calcium reduces absorption by up to 60%. Vitamin D without fat absorbs poorly. Magnesium in the morning misses its peak effectiveness window. The right timing can double the effectiveness of your supplement stack.
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ABOUT THIS TOOL
Built by Elthio Health
Timing recommendations are based on published pharmacokinetic research, NIH Office of Dietary Supplements guidance, and peer-reviewed absorption studies. 197+ timing rules covering the most common supplements. How we grade
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Based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature and peer-reviewed absorption research
Educational only — not medical advice.
Always confirm with your doctor or pharmacist.