Selenium to support your immune system

Middle-aged woman smiling. Takes Selenium to support her immune system.

Selenium to support your immune system

Selenium is an important trace element. It plays a positive role in supporting immune system function by helping fight off bacterial infections and viruses.

Selenium is known as a micronutrient and is required in very small amounts by the body. As a component of the enzyme glutathione peroxidase, which is a powerful antioxidant, it can help protect the brain, heart, and kidneys against free radicals and environmental toxins.

It maintains the health of male and female reproductive systems, regulates mood, blood pressure and assists with optimal thyroid function as well as cardiovascular health.

There is growing research to suggest that it can help with anti-ageing, by preserving skin elasticity and supporting brain function as we age.

As with zinc and iodine, New Zealand soils have been shown to have low levels of selenium, leading to deficiencies and predisposing us to certain illnesses, especially as we age. Selenium is now often added to foods such as bread in the form of imported selenium-rich wheat as well as added to animal and poultry feed on the farm.

Woman embracing young grand-daughter. There is growing research to suggest that selenium can help with anti-ageing.
There is growing research to suggest that selenium can help with anti-ageing.

Selenium was only recognised as an essential trace element for human health in 1990. Since then, we have learnt a great deal about its role within the human body, and the benefits it can provide.

The lack of selenium

New Zealand soils have low levels of a number of important minerals, including zinc, iodine and selenium. If these nutrients are not in our soils, they are not in the foods we eat.

In the NZ Nutrition Survey in 2009, the average dietary intake of selenium had improved, and was measured at 67mcg, up from 52mcg from the previous survey. Men and women over 71 years of age, and young women aged between 15-18 years had the lowest selenium intakes.

Essential as we age

Selenium activates the antioxidant enzyme glutathione peroxidase, which help mitigate the effects of ageing by removing environmental toxins from the body.

These toxins, or ‘free radicals’, can lead to inflammation, cardiovascular disease, cataract formation and a higher risk of various cancers.

A selenium-rich diet can also protect against premature ageing of the skin, by preserving the elasticity of arteries and our skin as we get older. It alleviates sun damage and age spots, helping to maintain a youthful appearance to the skin.

In females, research suggests adequate selenium status may reduce menopausal symptoms such as hot flashes.

What are free radicals?

Free radicals are often a product of our lifestyle, (such as excessive alcohol or smoking) or exposure to heavy metals and toxins in our environment. This exposure can occur through the water we drink, the foods we eat, or the air we breathe, as well as substances that come into contact with our skin.

These free radicals are molecules that have lost an electron and have become unstable. They go looking for an electron by attacking other cells within our body.

This causes damage to our cell walls and cell tissues, which impairs the function of the cell. This damage can then lead to degenerative diseases such as heart disease, autoimmune disorders, rheumatoid arthritis, and decreased thyroid function.

The antioxidant glutathione peroxidase attaches to the free radicals, providing the missing electron they need – which can prevent lasting damage to the body.

Woman drinking Skybright Selenium liquid mineral supplement.
Our body doesn’t produce selenium, so we must access it through our diet.

Maintaining mineral levels

As our body doesn’t produce selenium, concentrations of the mineral decline with age. Therefore, we must continue to access it through our diet, or look to supplement.

Low levels have been associated with age-related declines in brain function, possibly due to decreases in selenium’s antioxidant activity. More evidence is required to determine whether supplementing with selenium may help prevent or even treat cognitive decline in elderly people, which is a big issue facing this growing segment of the New Zealand population.

How much is needed?

In New Zealand, the recommended daily intake (RDI) for selenium is 60mcg for women and 70mcg for men. However, some nutritionists suggest a much higher RDI of 200mcg, temporarily increasing to 400mcg when fighting a viral infection, inflammation or a known heavy metal build-up.

While supplementing with selenium, other minerals such as iodine (from fish, shellfish) as well as vitamin E (sunflower seeds, almonds, peanuts) should also be part of the diet, as these nutrients all work well together to fight infection and inflammation.

Man drinking water with Skybright Selenium liquid mineral. In New Zealand, the recommended daily intake (RDI) for selenium is 60mcg for women and 70mcg for men.

In New Zealand, the recommended daily intake (RDI) for selenium is 60mcg for women and 70mcg for men. 

It’s important to remember that like some minerals, excessive selenium can be toxic, especially when supplementing in large quantities. When consuming more than 800-1000mcg (inorganic selenium) per day for long periods, you may experience symptoms of selenium toxicity, such as numbness in the hands and feet, a metallic taste in your mouth and bad breath.

In extreme cases, it can also cause skin rashes, gastrointestinal disturbance, brittleness and loss of fingernails, alopecia, irritability and nervous system abnormalities.

How to get selenium into your diet

It is well known that you can get your daily requirements of selenium from eating just a few brazil nuts. But this obviously depends on the selenium content in the soil in which they grow. The mineral content of the nuts can vary from as little as 10mcg to up to 100mcg in selenium-rich soil.

As with iodine, seafood provides a good source of selenium. Organ meats, poultry, eggs, dairy, cereals and unrefined grains are also good.

Unrefined grains, and Brazil nuts are good sources of dietary Selenium.
Unrefined grains and brazil nuts are good sources of dietary selenium.

Fruits and vegetables such as broccoli can contain selenium but again, only if they are grown in selenium-rich soils, which is often not the case in New Zealand. Soil pH, the amount of organic matter in the soil, geographic location and whether the selenium is in a form that is conducive to plant uptake are all factors.

For those on vegan, gluten-free, ketogenic or low-protein diets, selenium can be even harder to access. Selenium levels are often low if you suffer from malabsorption, diarrhoea or inflammatory bowel syndrome (IBS). Eat a whole-food diet where you can and try to limit foods and drinks that are high in sugars, saturated fats, and salt.

For those on vegan, gluten-free, ketogenic or low-protein diets, selenium can be even harder to access.

A hair mineral analysis test or a blood test can provide you with not only information on your current selenium status, but a range of other minerals that may be at low levels, due to diet or pre-existing conditions.

Iodine and selenium for thyroid health

Due to changes in diet and environmental factors, there has been an increase in thyroid disorders.

Both iodine and selenium are required for optimal thyroid function and work well together to support the health of the thyroid gland.

The antioxidant glutathione peroxidase is highly active in the thyroid gland, protecting it from oxidative damage. Low levels of selenium have been associated with reduced thyroid glutathione peroxidase activity and supplementation has in turn been shown to increase glutathione peroxidase activity. This protects the thyroid from excess iodine, and its potentially toxic effects.

Glutathione peroxidase is highly active in the thyroid gland, protecting it from oxidative damage.
Glutathione peroxidase is highly active in the thyroid, protecting it from oxidative damage.

In cases of iodine deficiency, selenium supplementation may too be of value, as deficiencies of selenium and iodine commonly co-exist.

There have been suggestions that selenium be added to table salt along with iodine, but table salt is not recommended as part of a healthy diet.Instead, unrefined sea salt is a better option as it contains many minerals and elements your body needs in trace amounts.

For more information, see our article Are you getting enough iodine?

Vitamin C to aid absorption

Vitamin C, often taken to assist our immune system, is another nutrient that works well with selenium. An intake of 600mg of Vitamin C has been shown to increase dietary selenium by nearly 100 percent.

Woman eating oranges while pregnant. An intake of 600mg of Vitamin C has been shown to increase dietary selenium by nearly 100%.
An intake of 600mg of Vitamin C has been shown to increase dietary selenium by nearly 100%.


Selenium works with a number of other nutrients, including iodine, vitamin E and vitamin C, to support our immune system and help tackle infections and inflammation.

It is an essential cofactor for glutathione peroxidase, an enzyme and antioxidant that helps protect us from damage caused by a range of pollutants and toxins that can be present in our environment, our food, and the water we drink. Our soils often have low levels of selenium, long with zinc and iodine, especially here in New Zealand.

Man holding glass of water. Taking selenium in liquid form increases bioavailability, enabling effective absorption of the mineral.
Taking selenium in liquid form increases bioavailability, enabling effective absorption of the mineral.

If we are unable to access the required amount of selenium due to diet or other factors, we can look to supplement, by taking just a few drops in a glass of water.

Taking selenium in liquid form increases bioavailability, meaning your body can quickly and effectively absorb the mineral. This can help boost your immune system and support your natural defences when tackling an infection.

It’s best to consult with your health professional before undergoing supplementation. They can also help you with assessing your mineral status through a blood test or by hair mineral analysis.

Coory, David. Stay Healthy by supplying what’s lacking in your diet. 1992
Schauss, Alexander G. Minerals, Trace Elements, & Human Health. Life Sciences Press. 1995
Christine D Thomson,  Jennifer M Campbell,  Jody Miller,  Sheila A Skeaff, Vicki Livingstone. Selenium and iodine supplementation: effect on thyroid function of older New Zealanders. 2009
Fairbairn, K. Serious about Selenium. Otago Daily Times. 2018
Medsafe. Selenium, Prescriber Update. 2000
National Institutes of Health (NIH) Selenium. Fact Sheet for Health Professionals. Updated 2021

The information in this article is not intended as a medical prescription for any disease or illness. Nothing stated here should be considered medical advice. Use as directed. If symptoms persist, consult your healthcare professional. 

Are you getting enough Iodine?

Woman holding mug and looking out to sea. Are you getting enough iodine?

Are you getting enough iodine?

When you hear the word iodine, you may think of the tablets used to disinfect water on camping trips or the yellow liquid used for disinfecting cuts and grazes when we were younger. Or you may just remember it from the periodic table in chemistry class.

Iodine is one of the most important life-sustaining elements. For more than 100 years, it has been known as the element that is necessary for thyroid hormone production. However, it is so much more than that.

Iodine is found in each and every one of the trillions of cells in the body, and responsible for the production of all the other hormones in the body.

It is a powerful antibiotic, and has potent antibacterial, antiviral properties.

It has strong anti-inflammatory effects by neutralising free radicals and is necessary for proper immune system function. Working together with other minerals like Selenium, it has many therapeutic benefits for a range of modern illnesses and diseases.

It is estimated by the World Health Organisation (WHO) that more than half of the world’s population live in an area of iodine deficiency, and that this has risen 400% in the last few decades due to soil depletion and an increase in environmental contaminants that have replaced it.

Our body does not make iodine, so we need to access it from the foods we eat. But if the nutrients are not in the soil to begin with, it cannot be in the food we eat, and this can lead to common deficiencies.

Iodine deficiency in New Zealand

Soil in coastal areas are naturally iodine-rich, as are the dairy products produced by the cows that graze there. Fresh produce such as fruits and vegetables that are grown in coastal areas are also rich in iodine.

Despite being a coastal nation, New Zealand soils are low in iodine, and this is reflected in our locally grown produce.

This can be due to intensive farming, lack of crop rotation and the use of fertilisers. Coupled with changes to our diet, the reduced use of iodised salt in the household, the prevalence of processed foods, many New Zealanders are now lacking important nutrients such as iodine that are key to good health.

The WHO’s research has suggested deficiencies in both Australia and New Zealand are re-emerging, when they were previously thought to be iodine sufficient.

This research suggests that we may be consuming less than 60% of what is recommended. While we all need iodine, it is especially important for women who are trying to fall pregnant, are currently pregnant or who are breastfeeding, as the body demands more during this time due to increased thyroid hormone production, and the requirements of the developing baby.

Woman smiling and leaning on fence in countryside.
Research suggests that we may be consuming less than 60% of what is recommended.

Properly evaluating and treating iodine deficiency will help people support thyroid health and immune system function, increase their energy levels, and help improve general health and wellbeing. This can be achieved by some simple changes to their diet or daily supplementation in consultation with their health practitioner. It can be as little as a couple of drops of potassium iodide in a glass of water each day to get you feeling better, and help you avoid some of the common but serious health problems we are seeing today in New Zealand and around the world.

The best results are seen with a holistic approach, and increasing the intake of important vitamins, minerals and electrolytes through a wholefood diet.

The hungry thyroid

The thyroid is often referred to as a ‘hungry’ part of the body, in reference to its high nutritional demands.

This butterfly-shaped endocrine gland surrounds the windpipe and is important for metabolism, regulating digestion and your heart rate. It facilitates energy production and mental agility. The thyroid also helps with fat burning too, by determining how quickly and efficiently kilojoules are burned up, and it assists in the breakdown of proteins. Thyroid function also assists the suppleness and strength of our hair, skin and nails.

Iodine is an essential ingredient in all thyroid hormones, including T4 (thyroxine) and T3 (triiodothyronine). It is important to maintain sufficient amounts of iodine, and they are required to be synthesised in adequate amounts. In a low thyroid state, known as hypothyroidism, the thyroid gland can’t make enough thyroid hormone to keep the body running normally. The metabolic state is therefore reduced which can lead to weight gain.

When the thyroid gland is releasing excess amounts of thyroid hormone, it is known as hyperthyroidism, which is an overactive or elevated metabolic state which can result in fatigue, irregular heartbeat, unexplained weight loss and brain fog.

When you have an adequate intake of iodine, your body contains 20-50g, and 75% of that amount is stored in the thyroid. However large amounts are also stored in other parts of the body, including the salivary glands, the breasts, ovaries, and the brain. In the brain it concentrates in the substantia nigra, the part of the brain that is associated with Parkinson’s disease.

One of the first signs of deficiency is an enlarged thyroid gland.

The lack of iodine causes the gland to expand in an attempt to extract as much iodine in the bloodstream as possible. If your iodine intake is low, this will be reflected in low levels of thyroid hormone. You may then experience fatigue, dry skin, constipation, systemic inflammation, a hoarse voice, delayed reflexes and some cognitive impairment.

It is best to consult your doctor or health professional should you identify any of these symptoms. Anybody taking thyroid medication should always discuss their condition with a health professional before taking supplementary iodine.

The role of selenium

Selenium, another important mineral and antioxidant, plays a significant role in regulating thyroid function and iodine metabolism. The thyroid contains more selenium by weight than any other organ in the body.

Selenium is a required component for the production of the enzyme glutathione peroxidase, which protects the body from damage with antioxidant capabilities.

Without this enzyme, the thyroid gland is susceptible to damage from oxidants, there would be no activation of thyroid hormone without selenium.

Pregnant woman lying on bed. Pregnant and breastfeeding women require more iodine.
Pregnant and breastfeeding women require more iodine.

The need for iodine before pregnancy

The consequences of iodine deficiency are most serious for women who are trying to fall pregnant, who are currently pregnant or are breastfeeding.

Thyroid hormones balance the function and development of the body’s major organs and influence the progress of the developing baby.

Research has shown that a lack of iodine can cause fetal and neonatal mental disabilities and growth problems, along with speech and hearing issues. Cognitive function and neurological development can be impaired when iodine levels are low.

Pregnant and breastfeeding women also require more iodine due to increased thyroid hormone production.

It is recommended that women take iodine supplements from the point of planned pregnancy and through the full duration of pregnancy as well as breastfeeding. Avoid kelp or seaweed supplements as they may be contaminated with heavy metals such as mercury. Multi-vitamin, multi-mineral and pre-natal supplements may or may not contain enough iodine, so it’s best to check.

Women with pre-existing thyroid conditions should always check with their health professional before taking a supplement.

How do I know if I’m deficient?

Under most states of iodine sufficiency, approximately 90% of dietary iodine eventually is excreted in the urine, with exception being the lactating female due to iodine excretion in the breast milk. Because of this, urine is the best biological fluid to use for assessment of deficiency.

If you are concerned there may be deficiency, you could undertake an iodine-loading test, otherwise known as a urinary iodine concentration (UIC) where you take a prescribed dose of iodine, then collect 24 hours of urine to undergo analysis with a health professional.

The principle of this test is that if you’re iodine sufficient, most of the dose will be excreted, and if there is a deficiency present, it will be instead be absorbed by the body.

Can I get enough iodine from salt?

Iodised table salt was implemented in many regions and countries around the world when iodine deficiency was recognised. In New Zealand in the 1920’s, the government allowed manufacturers to voluntarily add iodine to table salt. This was mainly to safeguard against thyroid enlargement (goitre) and the severe mental retardation of cretinism, although the incidence of these conditions was very rare in New Zealand.

Closeup image of unrefined, unprocessed sea salt. A better option than table salt.
Unrefined, unprocessed sea salt is a better option than table salt.

In recent decades we have seen people consume less salt due to health concerns, while some avoid salt entirely. Salt used in processed foods is often non-iodised to save on costs, so is not a source of iodine despite the sodium content.

In recent times we are seeing a prevalence of sea salt, or kosher salt, promoted as a healthier alternative. However, sea salt is a poor source of iodine, and we should look for unrefined, unprocessed sea salt, with some products now enriched with New Zealand sea kelp. The iodine in salt is not very bioavailable in our bodies, it is better absorbed through liquid and food sources. 

Other sources of dietary iodine

It can be difficult to identify sources and the quantity of iodine in most foods. However, it is naturally present in seawater, so therefore seafood is a good source, especially seaweed, shellfish and saltwater fish. It’s also naturally present in soil, and found in eggs and dairy, including yoghurt, cow’s milk, ice cream and cheese.

If you don’t have access to shellfish or other seafood, or if the soil is deficient due to intensive farming, you’ll need to access it from other sources.  

Iodine levels in milk can vary according to the soils in which the animals have grazed and factors such as the groundwater used in irrigation, fertilisers used and the feed for the livestock. Interestingly, organic milk is estimated to contain roughly 30-40% less iodine than conventional milk, owing to alternative processing methods.

It is difficult for most people to obtain adequate iodine by eating foods that are natural sources of iodine.

That said, in 2009, Iodine fortification of bread became mandatory with the exception of organic bread, non-yeast-leavened bread and bread mixes. When salt was iodised in the 20th century, this significantly improved the iodine levels within the New Zealand population, but recently deficiencies have again become apparent, hence the need for the fortification of foods.

Iodine dosage guidelines

There is no single dose of iodine that is effective for everyone. The best approach is working with a health professional that is knowledgeable about iodine.

If you eat seafood and other iodine-rich foods, use iodised salt, take a multi-vitamin or mineral supplement, you may be able to obtain adequate levels.

Recommended daily allowances range from 100-250mcg a day, with the exception of pregnant or breastfeeding women, who may require more than 300mcg per day due to increased hormone production in early pregnancy, increased urinary iodine excretion, and the transfer of iodine to the fetus or the nursing infant when feeding.

Some leading iodine experts suggest significantly larger daily doses, even up to 12mg. In Japan, the average daily intake is 12-13 milligrams due to increased consumption of seaweed and other seafood.

Iodine Liquid Mineral: Just 2 drops a day = 255mcg of Potassium Iodide


Iodine is one the most basic elements of all life on earth, it is present in the ocean, marine life and in every one of the trillions of cells in our body. The role it plays in our everyday wellbeing cannot be overstated. As our bodies can’t produce iodine, there are simple steps we can take to make sure we can rebalance and replenish our mineral levels, and avoid deficiencies.

Brownstein, MD. D. Iodine. Why You Need It And Why You Can’t Live Without It. 2014
Reader’s Digest. The Healing Power of Vitamins, Minerals & Herbs. 2000
Schauss, Alexander G. Minerals, Trace Elements, & Human Health. Life Sciences Press. 1995
Kohrle J. The Trace Element Selenium and The Thyroid Gland. Biochimie. 1999
Smallridge RC, Ladenson PW. Hypothyroidism In Pregnancy: Consequences To Neonatal Health. J Clin Endocrinol Metab. 2001
Iodine. Ministry of Health Manatū Hauora Website.
Editors: de Benoist, Bruno. Andersson, Maria. Iodine status Worldwide. WHO Global Database on Iodine Deficiency. World Health Organisation, Geneva. 2004
Ministry of Health Manatū & Australian National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand Including Recommended Dietary Intakes. 2006, updated 2017.

The information in this article is not intended as a medical prescription for any disease or illness. Nothing stated here should be considered medical advice. Use as directed. If symptoms persist, consult your healthcare professional.