Selenium

Selenium – The Antioxidant Mineral

Selenium is a powerful trace mineral that supports thyroid health, immune function, and antioxidant protection. It helps your body fight oxidative stress, maintain a healthy metabolism, and reduce inflammation.

While Brazil nuts are famously rich in selenium, many other foods also provide this essential nutrient.

Why Selenium Is Important

• Supports Thyroid Function – Selenium is needed to convert inactive thyroid hormone (T4) into its active form (T3). Having good levels of T3 is crucial because it is part of a process that activates and recycles many vitamins, such as B1, B2, B3, B6, B9, B12, vitamin A, and Vitamin K. Without enough T3, these vitamins will not function effectively.

• Antioxidant Protection – It's a key component of antioxidant enzymes that protect cells from damage.

• Immune Health – Selenium boosts the immune system and helps fight infections.

• Fertility & Hormone Balance – Plays a role in sperm quality and reproductive health.

Signs of Selenium Deficiency

Selenium deficiency can occur because many regions in the world have selenium-poor soil (such as the UK), and due to a poor diet and gut absorption issues.

Symptoms may include:

• Fatigue or muscle weakness

• Brittle hair or nails

• Slow thyroid function (hypothyroidism)

• Low immunity and frequent infections

• Brain fog or poor concentration

Recommended Daily Intake (RDI)

• Adults: 55 mcg/day

• Pregnant Women: 60 mcg/day

• Breastfeeding Women: 70 mcg/day

(Note: Selenium is required in tiny amounts — both deficiency and excess can cause problems.)

Top Food Sources of Selenium (No Brazil Nuts)

Tuna (yellowfin): 100g cooked = 92 mcg

Sardines: 100g canned = 52 mcg

Chicken breast: 100g cooked = 31 mcg

Turkey: 100g cooked = 27 mcg

Eggs: 1 large = 20 mcg

Cottage cheese: 1 cup (220g) = 20 mcg

Sunflower seeds: 30g (¼ cup) = 19 mcg

Brazil nuts are one of the richest sources of selenium; however, most of it is in the form of selenomethionine. To use selenium in selenomethionine efficiently, your body needs a healthy methylation pathway. If this system is slow or blocked, your body may struggle to process selenomethionine into the active forms that it needs, and so not benefit from it.

Why Keeping a 5-Day Food Diary is So Helpful (Especially with a Free App Like Cronometer)

If you've ever wondered whether you're getting enough vitamins and minerals from your diet, keeping a food diary for just 5 days can be a real eye-opener. Using a free app like Cronometer makes the process simple and surprisingly insightful.

Cronometer doesn't just track calories — it gives you a full nutritional breakdown of the food you eat each day. You’ll quickly see where your diet is strong and where you might be missing out on important nutrients like B12, magnesium, or iron.

One of the best things about using an app like this is that you can experiment. Try swapping in nutrient-dense foods — such as chicken liver, beets, or romaine lettuce — and see how even small changes can dramatically improve your nutrient intake.

If you're using my example one-day meal plans for specific vitamins and minerals, keep in mind: they're just examples to show what's possible. Cronometer helps you take it a step further by tailoring things to your own diet, preferences, and needs.

Tracking your eating habits for just 5 days can give you a clearer picture of how they support your health — and where a few smart tweaks can make all the difference.

Example Meal Plan to Meet the RDI

Here's an example of how to get ~70–90 mcg of selenium without Brazil nuts:

Breakfast:

2 boiled eggs (40 mcg)

1 cup cottage cheese (20 mcg)

Lunch:

Grilled chicken breast (100 g – 31 mcg)

Mixed salad with sunflower seeds (30 g – 19 mcg)

Snack:

1 small tin of sardines (50 g – 26 mcg)

Dinner:

Baked salmon or tuna steak (100 g – 92 mcg)

Steamed vegetables

Total: ~140–150 mcg selenium (well over the RDI, but still safe)

Selenium Supplements – Do You Need Them?

Most people can meet their nutritional needs through a balanced diet, especially if they include foods like fish, eggs, and seeds.

Vegans are at risk of deficiency in regions where the soil is selenium-deficient, such as the UK.

Supplements are usually not necessary unless you have a restricted diet or a confirmed deficiency.

Warning:

Taking too much selenium can generate oxidative stress, causing issues like hair loss, nausea, or a metallic taste in the mouth — so avoid high-dose supplements unless advised by a professional.

Hashimoto's, Graves', or HIV are conditions where supplementation may be beneficial. Most studies have used 200 mcg/d. One study showed a 40 % reduction in antibody levels after selenium supplementation, with 25% of patients completely normalising their antibody levels.

The selenium should be as Selenite salt, but should not be Selenomethionine or Selenium chelates, or Selenium amino acids complex, each of which has been shown not to work by Dr G. Russell-Jones' research (see B12oil.com for more information).

There must be no divalent cations in the formulation (such as calcium, magnesium, iron, zinc, copper or manganese) as these bind to the Selenite, forming insoluble compounds that we are unable to absorb. To avoid this issue, there is a topical skin oil available at B12oils.com

We use Vitamaze Sodium Selenite, available from Amazon using this link (paid link).

Vitamaze Sodium Selenite

Key Takeaways (Cheat Sheet)

• RDI: 55 mcg/day for adults

• Best Sources: Tuna (100g = 92 mcg), Sardines (100g = 52 mcg), Chicken breast (100g = 31 mcg), Eggs (1 egg = 20 mcg), Sunflower seeds (30g = 19 mcg)

• Deficiency Signs: Fatigue, brittle hair/nails, low immunity, thyroid issues

• Tip: A portion of tuna or two eggs + chicken easily meets daily needs

For more information, please visit https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/

This information is provided for educational purposes only and should not be considered medical advice.