Spotlight: Magnesium 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 affect them. It is not a substitute for personalised medical advice. Every NET patient is different — tumour type, treatments, surgery, symptoms, and nutritional needs can vary widely. If you have concerns about vitamin levels, supplements, or symptoms, please speak with your NET clinical team. They can assess your individual situation and guide you safely.

Magnesium is a vital mineral involved in numerous physiological processes including muscle function, nerve transmission, heart rhythm regulation, and enzyme activity. For patients with Neuroendocrine Tumours (NETs), maintaining adequate magnesium levels is particularly important due to factors that can predispose to deficiency. Hypomagnesemia often occurs alongside low calcium and potassium levels, and these other deficiencies won’t correct until magnesium is restored first.

Causes of Magnesium Deficiency in NETs

Somatostatin Analogues Without Chronic Diarrhoea: Even NET patients on somatostatin analogues who do not experience chronic diarrhoea may have reduced magnesium absorption due to the drug’s inhibitory effects on intestinal transport mechanisms.
Malabsorption and Diarrhoea: Many NET patients experience chronic diarrhoea, which can lead to significant magnesium loss.
VIPoma: A rare functional pancreatic NET causing profuse secretory diarrhoea due to excess vasoactive intestinal peptide (VIP), resulting in significant electrolyte and magnesium depletion.
Surgical Resection: Removal of parts of the gastrointestinal tract can impair magnesium absorption.
Somatostatin Analogues: These treatments can reduce intestinal absorption of magnesium.
Proton Pump Inhibitors (PPIs): Long-term use of PPIs, common in NET patients for acid-related issues, can reduce magnesium absorption.

Why Magnesium Gets Malabsorbed

Magnesium absorption primarily occurs in the small intestine, especially in the distal sections, through both passive and active transport mechanisms. The ileum is the main site, responsible for about 56% of absorption, followed by the jejunum and duodenum. The large intestine, particularly the colon, also contributes to magnesium absorption but to a lesser extent. Absorption occurs via two main pathways: an active transport system through TRPM6/7 channels, which is important at low magnesium intake, and a passive diffusion route that predominates when magnesium levels in the gut are higher. This is why splitting magnesium intake into smaller doses can improve absorption efficiency.

Malabsorption can result from several factors:

Gastrointestinal Disorders: Conditions such as Crohn’s disease, celiac disease, inflammatory bowel disease, and short bowel syndrome damage the intestinal lining or reduce absorptive surface area, impairing magnesium uptake.
Chronic Diarrhoea: Leads to direct loss of magnesium through intestinal fluids.
Surgical Resection: Removal of parts of the small intestine reduces the area available for absorption, particularly if the ileum is affected.
Medications: Proton pump inhibitors (PPIs) impair magnesium absorption by affecting intestinal transport channels (TRPM6/7). Diuretics can increase renal magnesium loss.
Other Factors: High levels of dietary inhibitors (phytates, oxalates), aging, and alcohol use can also reduce absorption or increase losses.

Hypomagnesemia and Associated Electrolyte Deficiencies

Hypomagnesemia often occurs alongside low calcium (hypocalcemia) and low potassium (hypokalemia) levels. These deficiencies are interrelated because magnesium is essential for the secretion and function of parathyroid hormone (PTH), which regulates calcium levels, and for the normal functioning of the sodium-potassium ATPase pump, which maintains potassium balance. As a result, hypocalcemia and hypokalemia typically will not correct until magnesium levels are restored first. Magnesium deficiency suppresses PTH secretion and causes resistance to PTH at target organs, making calcium supplementation ineffective until magnesium is replenished. Similarly, magnesium is required for potassium retention in cells, so low magnesium leads to ongoing potassium loss. This clinical relationship is well documented in medical guidelines and clinical biochemistry references.

NET Patients Most at risk of Magnesium Malabsorption

Certain NET patients are more prone to magnesium malabsorption due to their disease or treatment-related factors:

Patients with Chronic Diarrhoea: Common in NETs secreting serotonin or those treated with somatostatin analogues, leading to increased magnesium loss. This group also includes patients with VIPoma, a rare functional pancreatic NET that causes profuse secretory diarrhea due to excess vasoactive intestinal peptide (VIP), resulting in significant electrolyte and magnesium depletion. Magnesium is both a vital mineral and an essential electrolyte, meaning it carries an electrical charge in body fluids, which is crucial for many physiological functions.
Patients with Gastrointestinal Surgery: Those who have had resections involving the ileum or other parts of the small intestine have reduced absorptive capacity.
Patients on Long-Term PPIs: Often prescribed for acid-related symptoms or gastrinomas (Zollinger-Ellison Syndrome), PPIs reduce magnesium absorption by interfering with TRPM6/7 channels.
Patients with Malabsorptive Syndromes: NET patients with coexisting conditions like celiac disease or inflammatory bowel disease may have compounded absorption issues.

Understanding these factors helps tailor monitoring and supplementation strategies for NET patients at risk of magnesium deficiency. Certain NET patients are more prone to magnesium malabsorption due to their disease or treatment-related factors:

Patients with Chronic Diarrhoea: Common in NETs secreting serotonin or those treated with somatostatin analogues, leading to increased magnesium loss.
Patients with Gastrointestinal Surgery: Those who have had resections involving the ileum or other parts of the small intestine have reduced absorptive capacity.
Patients on Long-Term PPIs: Often prescribed for acid-related symptoms or gastrinomas (Zollinger-Ellison Syndrome), PPIs reduce magnesium absorption by interfering with TRPM6/7 channels.
Patients with Malabsorptive Syndromes: NET patients with coexisting conditions like celiac disease or inflammatory bowel disease may have compounded absorption issues.

Gastrointestinal Disorders: Conditions such as Crohn’s disease, celiac disease, inflammatory bowel disease, and short bowel syndrome damage the intestinal lining or reduce absorptive surface area, impairing magnesium uptake.
Chronic Diarrhoea: Leads to direct loss of magnesium through intestinal fluids.
Surgical Resection: Removal of parts of the small intestine reduces the area available for absorption, particularly if the ileum is affected.
Medications: Proton pump inhibitors (PPIs) impair magnesium absorption by affecting intestinal transport channels (TRPM6/7). Diuretics can increase renal magnesium loss.
Other Factors: High levels of dietary inhibitors (phytates, oxalates), aging, and alcohol use can also reduce absorption or increase losses.

Magnesium absorption involves two main pathways: an active transport system via TRPM6/7 channels and a passive diffusion route. The active pathway is saturable and critical at low magnesium intake, while the passive route predominates at higher intake levels. This explains why splitting magnesium supplements into smaller doses can improve absorption efficiency.

Symptoms of Magnesium Deficiency

Muscle cramps and spasms
Fatigue and weakness
Palpitations and arrhythmias
Mood changes including anxiety and irritability

Understanding magnesium as both a mineral and an electrolyte highlights its critical role in overall electrolyte homeostasis, especially in NET patients who may experience imbalances due to disease or treatment.

Symptoms of Magnesium Deficiency

Muscle cramps and spasms
Fatigue and weakness
Palpitations and arrhythmias
Mood changes including anxiety and irritability

Risk Levels of Magnesium Deficiency

Magnesium deficiency risk can be classified based on severity and clinical context:

Low Risk: Individuals with normal dietary intake and no underlying gastrointestinal or renal conditions generally have a low risk of magnesium deficiency.
Medium Risk: Patients with mild malabsorption, intermittent diarrhea, or on medications like proton pump inhibitors (PPIs) or diuretics may have a moderate risk.
High Risk: Patients with chronic diarrhea (such as those with VIPoma or serotonin-secreting NETs), significant gastrointestinal surgery (especially ileal resection), long-term PPI use, or renal magnesium wasting are at high risk of deficiency. Severe deficiency can lead to serious complications including cardiac arrhythmias and neurological symptoms.

Clinical assessment and laboratory testing are essential to identify and manage magnesium deficiency appropriately.

Assessing Magnesium Status

Serum magnesium levels may not accurately reflect total body magnesium stores since most magnesium is intracellular. Clinical assessment and consideration of risk factors are essential.

Testing for Magnesium Deficiency

Testing for magnesium deficiency involves several approaches due to the complexity of magnesium distribution in the body:

Serum Magnesium: The most common test but reflects only about 1% of total body magnesium and may not detect mild deficiency.
24-hour Urinary Magnesium: Helps assess renal magnesium loss; low urinary magnesium in the presence of hypomagnesemia suggests poor intake or absorption, while high levels indicate renal wasting.
Clinical Symptoms and Risk Factors: Symptoms such as muscle cramps, arrhythmias, and fatigue combined with risk factors (e.g., chronic diarrhea, PPI use, gastrointestinal surgery) guide diagnosis.
Other Tests: Intracellular magnesium measurements (e.g., in red blood cells) and magnesium loading tests exist but are less commonly used due to complexity.

Clinical Guidelines on Testing and Management

Clinical guidelines recommend regular monitoring of serum magnesium in patients at risk, especially those on long-term PPIs, somatostatin analogues, or with chronic diarrhoea or gastrointestinal surgery. Treatment decisions are based on severity, symptoms, and underlying causes.

Mild deficiency (0.5-0.7 mmol/L) may only require oral supplementation if symptomatic.
Moderate deficiency (0.4-0.5 mmol/L) often requires oral supplementation and sometimes intravenous replacement if symptomatic.
Severe deficiency (<0.4 mmol/L) usually requires urgent intravenous magnesium replacement and hospital admission.

Monitoring should also include other electrolytes such as potassium and calcium due to their interrelated roles.

Relationship with Vitamin D

Magnesium acts as a helper tool (cofactor) for the enzymes that turn vitamin D into its active form in your liver and kidneys.

If you lack magnesium, your body may struggle to process or use vitamin D supplements properly.

Resources

1. 1. NHS Magnesium Guidance
  2. NIH Office of Dietary Supplements – Magnesium Fact Sheet
  3. Hypomagnesaemia – Basic Information
  4. Vitamin deficiencies in patients with neuroendocrine tumours
  5. Park CH, Kim EH, Roh YH, Kim HY, Lee SK. The Association between the Use of Proton Pump Inhibitors and the Risk of Hypomagnesemia: A Systematic Review and Meta-Analysis. PLoS One. 2014;9(11):e112558. doi:10.1371/journal.pone.0112558
  6. Royal United Hospitals Bath NHS Foundation Trust. Hypomagnesaemia – a guide for GPs. Clinical Biochemistry Department; 2024.
  7. Northern Treatment Advisory Group. Management of Acute Hypomagnesaemia in Adults in Primary Care. 2021.
  8. ENETS and NANETS guidelines on monitoring electrolyte imbalances and nutritional status in NET patients (various publications).

Others in the Series

Iron – click here

Zinc – click here

Potassium – click here

Selenium – 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.

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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.