Quick answer
NIH's fact sheets do not name a best time of day for selenium, and the body absorbs up to about 90% of it from common supplement forms. In a small study, a light breakfast barely changed absorption of sodium selenite, but taking it mixed with 1 g of vitamin C on an empty stomach cut absorption almost to zero.1,2
Key facts
- Dietary selenium is readily absorbed, and how much is absorbed is largely unaffected by how much selenium a person already has.1
- In a small study of selenite absorption, orange juice with breakfast, about 60 mg of vitamin C, appeared to help rather than hinder it.2
- In young men, a diet low in vitamin C, about 20 mg a day, was linked with lower selenite absorption than a diet with 1 g a day.3
- In a 12-week trial, blood selenium kept rising for about 10 weeks of daily intake before it leveled off.4
Morning or night?
None of the sources we used compared morning and evening doses of selenium, and NIH gives no advice on the hour. What the research does show is that blood selenium builds up over weeks of daily intake, so a time you will remember every day counts for more than which time it is.1,4
If your selenium comes in a multivitamin, follow the directions on that product's label, since its other ingredients may come with their own advice.
With food or on an empty stomach
In a small study of 10 young women given 1 mg of selenium as sodium selenite, a light breakfast had little effect on how much was absorbed, and orange juice appeared to help.2
The test dose in that study was 1 mg of selenium, far above the 400 mcg daily upper limit, given once after an overnight fast and tracked in urine and stool for five days. The study was small and old, and it tested only sodium selenite.2,5
In food, selenium is mostly selenomethionine, along with some selenocysteine.1
That is the form your body handles every time you eat fish, meat, eggs or bread, and NIH describes dietary selenium as readily absorbed. Nothing in these sources suggests you need an empty stomach for selenium.1
Vitamin C and selenite
In the same study, taking the selenite mixed with 1 g of vitamin C on an empty stomach cut the selenium absorbed almost to zero.2
A second small study points the other way over the longer term: young men absorbed and kept less of a selenite dose on a diet with little vitamin C than on one with 1 g a day. Read together, the two suggest the problem is a large vitamin C dose mixed with selenite at the same moment, not vitamin C in your everyday diet. Neither study tested selenomethionine or selenium yeast.2,3
Check the form on the label
The Supplement Facts panel names the form, such as selenomethionine, selenium yeast, sodium selenite or sodium selenate. The vitamin C finding applies to sodium selenite, the form those timing studies used. In a separate 16-week trial, urine measurements suggested selenomethionine was absorbed better than selenite.2,5,6
If you take thyroid medicine or have chemotherapy
The levothyroxine label asks that the medicine be taken on an empty stomach, half an hour to an hour before breakfast, and kept apart from iron and calcium supplements and antacids, which can lower its absorption. The label does not mention selenium, which is not a finding either way. If your selenium comes in a multivitamin, check whether it also lists calcium or iron, and ask your pharmacist how to time it.7
- Ask your doctor first if you have a thyroid condition
- Ask your cancer care team before taking selenium during chemotherapy: cisplatin can lower selenium levels5
Questions people ask
Should I take selenium in the morning or at night?
The evidence does not favor either. No study we found compared the two, and the absorption research looked at meals and vitamin C rather than the hour. Pick a time you will remember every day.2
Can I take selenium with vitamin C?
In one small study, 1 g of vitamin C mixed with sodium selenite on an empty stomach left almost none of the selenium absorbed, while orange juice with breakfast caused no such problem. If your product uses sodium selenite, it is reasonable to take a large vitamin C supplement at a different time of day. The studies did not test selenomethionine.2
Can I take selenium on an empty stomach?
As far as these studies show, yes. Absorption of dietary selenium is largely unaffected by how much a person already has, and a light meal made little difference to selenite absorption. The one problem found was a large vitamin C dose taken at the same moment.1,2
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Sources
- National Institutes of Health, Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals. Updated September 4, 2025. Opened 2026-10-07.
- Robinson MF, Thomson CD, Huemmer PK. Effect of a megadose of ascorbic acid, a meal and orange juice on the absorption of selenium as sodium selenite. N Z Med J. 1985;98(784):627-629. Opened 2026-10-07.
- Martin RF, Young VR, Blumberg J, Janghorbani M. Ascorbic acid-selenite interactions in humans studied with an oral dose of 74SeO3(2-). Am J Clin Nutr. 1989;49(5):862-869. Opened 2026-10-07.
- Hurst R, et al. Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2010;91(4):923-931. Opened 2026-10-07.
- Office of Dietary Supplements, National Institutes of Health. Selenium: Fact Sheet for Consumers. Updated June 18, 2025. Opened 2026-10-07.
- Burk RF, et al. Effects of chemical form of selenium on plasma biomarkers in a high-dose human supplementation trial. Cancer Epidemiol Biomarkers Prev. 2006;15(4):804-810. Opened 2026-10-07.
- SYNTHROID (levothyroxine sodium) tablets: prescribing information (AbbVie). DailyMed, U.S. National Library of Medicine. Published February 29, 2024. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.