Spotlight: Selenium in Neuroendocrine Tumours (NETs)

Before you read this

This information is designed to help you understand how vitamins and minerals work in the body and how certain NET‑related factors might influence them. It is not a substitute for personalised medical advice. Every NET patient is different — tumour type, treatments, surgery, symptoms, and nutritional needs vary widely. If you have concerns about selenium levels, supplements, or symptoms, please speak with your NET clinical team.

What Selenium Is

Selenium is an essential trace element required for the function of several selenoproteins involved in:

Antioxidant defence
Redox regulation
Thyroid hormone metabolism
Immune function
Cellular protection

Although needed only in tiny amounts, selenium plays a disproportionately important role in maintaining cellular stability — something relevant for NET patients who may experience chronic inflammation, malabsorption, or treatment‑related digestive changes.

Where the Body Gets Selenium

Selenium must come from diet or supplements. Main dietary sources include:

Brazil nuts
Fish and seafood
Meat and poultry
Eggs and dairy
Whole grains and legumes

In food, selenium is mostly present as selenocysteine and selenomethionine, bound to proteins and released during digestion.

High‑Level Signs of Selenium Deficiency

Symptoms can be subtle and overlap with other conditions:

Fatigue
Muscle weakness
Hair loss or brittle nails
Increased susceptibility to infections
Cognitive fog or mood changes
Thyroid dysfunction

Severe deficiency is rare but can affect heart and immune function.

Is Selenium a Common Deficiency in NET Patients?

There is no evidence of widespread selenium deficiency across the entire NET population. Large epidemiological studies simply don’t exist for this micronutrient in NETs. However, selenium is still considered an “at‑risk” mineral in certain NET subgroups because of well‑established physiological mechanisms that increase the likelihood of deficiency. ENETS guidance emphasises that malnutrition and micronutrient deficiencies are common in NET patients with diarrhoea, pancreatic insufficiency, small‑bowel resections, and somatostatin analogue therapy. Selenium fits into this broader category of micronutrients affected by malabsorption. NANETS acknowledges nutritional risk but does not list selenium as a routine deficiency.

NET Patients Most at Risk of Selenium Deficiency

Small‑bowel NETs with chronic diarrhoea
Pancreatic NETs with exocrine insufficiency
Patients with small‑bowel resections
Patients on long‑term SSAs
Patients on long‑term PPI therapy, as reduced gastric acidity and altered protein digestion can make selenium absorption less efficient in those who already have NET‑related malabsorption risks
Patients with coexisting malabsorptive conditions (IBD, coeliac disease, Crohn’s)

These factors reduce protein digestion, contact time, and absorptive surface, making selenium deficiency more likely — though not universal.

How Selenium Is Absorbed

Absorption occurs mainly in the duodenum and proximal jejunum, through:

Amino‑acid transport pathways (for selenomethionine)
Passive diffusion (for selenite/selenate)

Absorption efficiency is normally high (50–80%), but NET‑related factors can significantly reduce this.

Testing for Selenium

Assessing selenium status can be helpful, but testing has important limitations. Serum selenium is the most commonly available test, yet it mainly reflects recent intake rather than long‑term or functional selenium activity. This means that mild or early deficiency may not always be detected, especially in patients with complex malabsorption patterns. More accurate functional markers — such as glutathione peroxidase (GPx) activity or selenoprotein P — provide a better indication of how selenium is actually being used in the body. However, these tests are not routinely available in standard clinical practice and are generally limited to specialist centres or research settings. Because of these limitations, clinicians typically interpret selenium results in combination with symptoms, risk factors, and overall nutritional status, rather than relying on a single laboratory value. This approach is particularly important in NET patients, where factors such as diarrhoea, somatostatin analogue therapy, pancreatic insufficiency, small‑bowel resections, and long‑term PPI use can influence selenium absorption without always producing clear changes in serum levels. In practice, selenium testing is most useful when:

A patient has clear risk factors for malabsorption
Symptoms suggest a possible deficiency
Supplementation needs to be guided safely
Other micronutrient deficiencies are already present

Testing is therefore a supportive tool, not a definitive measure, and results should always be interpreted within the broader clinical picture.

Dangers of Over‑Supplementation (Selenosis)

Selenium has a narrow safe range. Excess intake — almost always from supplements — can cause:

Hair loss
Nail brittleness
Metallic taste
Gastrointestinal upset
Fatigue or irritability
Peripheral neuropathy
Liver enzyme abnormalities

Food‑based selenium almost never causes toxicity. Supplementation should be clinician‑guided, especially in NET patients with complex GI physiology.

Key Takeaways for NET Patients

Selenium is essential for antioxidant defence, thyroid function, and immune regulation.
NET‑related diarrhoea, SSAs, pancreatic insufficiency, small‑bowel resections, and long‑term PPI use can reduce selenium absorption.
Selenium deficiency is not universal, but at‑risk in specific NET subgroups.
Testing is helpful but imperfect — results must be interpreted in context.
Supplements should be clinician‑guided to avoid toxicity.

References (selected)

NHS Selenium Guidance
NIH Office of Dietary Supplements – Selenium Fact Sheet
ENETS Consensus Guidelines — nutrition, malabsorption, micronutrient risk
ENETS 2023–2024 updates — malnutrition in NET subgroups
NANETS Consensus Guidelines — nutritional considerations

Others in the Series

Iron – click here

Zinc – click here

Magnesium – click here

Potassium – click here

Disclaimer

I am not a doctor or any form of medical professional, practitioner or counsellor. None of the information on my website, or linked to my website(s), or conveyed by me on any social media or presentation, should be interpreted as medical advice given or advised by me. Neither should any post or comment made by a follower or member of my private group be assumed to be medical advice, even if that person is a healthcare professional. Please also note that mention of a clinical service, trial/study or therapy does not constitute an endorsement of that service, trial/study or therapy by Ronny Allan, the information is provided for education and awareness purposes and/or related to Ronny Allan’s own patient experience. This element of the disclaimer includes any complementary medicine, non-prescription over the counter drugs and supplements such as vitamins and minerals.