Health Reference LibraryHow much selenium should I take, and how much is too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Fifty to a hundred micrograms a day closes the gap between a UK diet and the reference intake of 75 micrograms for men and 60 for women, and one or two Brazil nuts do the same, so the 200 microgram capsule is a full dose that should be the only selenium you take. The NHS says 350 micrograms a day from supplements is unlikely to cause harm, and selenosis, with brittle hair and nails, hair loss and a garlic smell on the breath, starts above about 400 micrograms a day from all sources over time. Count every product that contains selenium before adding another, and ask your GP first if a thyroid condition is under their care.
Dose calculator: capsules to reach your selenium target
Enter the daily amount of selenium you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is 75 micrograms a day for men and 60 micrograms for women. Selenium is a mineral where more is not better. For most people 50 to 100 micrograms a day closes the gap between a UK diet and the reference intake; one or two Brazil nuts do the same. The 200 microgram capsule is a full supplement dose and should be the only selenium you take; do not add it to a multivitamin that already carries 50 to 100 micrograms. A tested low level, with your GP, is the case for 200 micrograms.
Safety profile
How much is too much: the NHS says 350 micrograms or less a day from supplements is unlikely to cause harm; signs of too much appear above about 400 micrograms a day over time. Too much selenium over months causes selenosis: brittle hair and nails, hair loss, a garlic smell on the breath, tiredness and irritability. It starts above about 400 micrograms a day from all sources, which is easy to reach by stacking a capsule, a multivitamin and Brazil nuts. Stay under 350 micrograms a day from supplements and count every product that contains it. Anyone under the care of a GP for a thyroid condition asks first.
Guideline positions
NHS vitamins and minerals guidance for selenium. NIH Office of Dietary Supplements fact sheet for selenium where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [selenomethionine capsules](/products/selenium-methionine), 200 micrograms per capsule, one a day, the store building form; [SeMSC capsules](/products/selenium-semsc), 200 micrograms per capsule, one a day, taken away from food. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more selenium works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- 2024. Selenium: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements.
- NHS (UK government) 2025. Vitamins and minerals: others (zinc section). NHS.uk.