A blog by Ronny Allan

Neuroendocrine Tumours – Vitamin B3 (Niacin)

Neuroendocrine Tumours – Vitamin B3 (Niacin)

Before you read this
This information is designed to help you understand how vitamins 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.


What Vitamin B3 Is

Vitamin B3 — also known as niacin, nicotinamide, or nicotinic acid — is an essential water‑soluble vitamin your body uses to convert food into energy. It supports healthy skin, nerves, digestion, and plays a central role in cellular repair and NAD⁺ production, which keeps cells functioning normally.

There are two main forms:

  • Nicotinic acid – affects blood vessels and cholesterol
  • Nicotinamide (niacinamide) – used in most supplements; does not cause flushing

Both ultimately support the same vitamin functions.

 

Why Vitamin B3 Matters

Vitamin B3 is required to make NAD⁺, a molecule involved in:

  • Energy production
  • DNA repair
  • Cellular resilience
  • Detoxification pathways

Low levels can contribute to:

  • Fatigue
  • Skin irritation
  • Digestive discomfort
  • Cognitive fog

Severe deficiency leads to pellagra, though this is rare in NETs today.

 

How the Body Gets Vitamin B3

You obtain B3 from:

  • Food (meat, fish, eggs, nuts, seeds, whole grains)
  • Conversion from tryptophan, an amino acid
  • Supplements, when needed

Because the body stores very little, regular intake is important.


Vitamin B3 and Neuroendocrine Tumours (NETs)

Most NET patients maintain normal Vitamin B3 levels. However, certain NET‑related factors increase the risk of deficiency.

 

1. Carcinoid Syndrome and Tryptophan Diversion

This mechanism is important — but clinically significant B3 deficiency is now far less common than it used to be.

Top Bullet:

Serotonin secreting NETs (carcinoid syndrome) divert tryptophan into serotonin production, leaving too little available for the body to make Vitamin B3 (niacin).

Why this matters

  • Tryptophan is the raw material the body uses to make niacin
  • Serotonin‑producing NETs can consume large amounts of tryptophan
  • Even with a good diet, the body may not have enough left to produce niacin
  • This creates a functional B3 deficiency, independent of diet

Why it’s less common today

Modern NET care has dramatically reduced the frequency of severe tryptophan diversion:

  • Somatostatin analogues (SSAs) suppress serotonin production, reducing tryptophan consumption
  • Earlier diagnosis means fewer patients reach extreme serotonin‑overproduction states
  • Better diarrhoea control reduces nutrient loss
  • Improved nutritional support catches issues earlier

Who is most at risk today?

  • Patients with active, uncontrolled carcinoid syndrome
  • Those with very high serotonin output
  • Patients with significant diarrhoea or malabsorption
  • Individuals with extensive small bowel disease or resections

For most patients on stable treatment, Vitamin B3 deficiency is uncommon, but the mechanism remains important to understand.

 

2. Somatostatin Analogues (SSAs)

Medications like octreotide and lanreotide can reduce absorption of several nutrients. B3 deficiency is less common than B12 or fat‑soluble vitamin issues, but still possible due to:

  • Reduced digestive enzyme activity
  • Reduced mucosal absorption
  • Faster or slower transit depending on the patient
 

3. Digestive Surgery or Malabsorption

Small bowel resections, rapid transit, or chronic diarrhoea can reduce absorption of:

  • Tryptophan
  • Niacin itself

Because water‑soluble vitamins are not stored, even mild malabsorption can lead to deficiency over time.

 

Symptoms of Low Vitamin B3

Symptoms can be subtle and overlap with other conditions:

  • Persistent fatigue
  • Headaches
  • Irritability or low mood
  • Dry or inflamed skin
  • Diarrhoea
  • Poor appetite
  • Difficulty concentrating

More significant deficiency may cause:

  • Sun‑sensitive skin rashes
  • Mouth soreness
  • Severe diarrhoea
  • Cognitive changes

Any of these warrant clinical review.

 

Testing Vitamin B3 Levels

There is no single routine blood test for niacin status. Clinicians may assess:

  • Symptoms
  • Dietary intake
  • Tryptophan metabolism markers
  • NAD/NADP ratios (specialist labs only)

Testing is guided by risk factors and clinical presentation.

 

Supplementation

Supplementation should be guided by your clinical team.

Key points:

  • Nicotinamide is usually preferred for general supplementation
  • Nicotinic acid can cause flushing and is mainly used for cholesterol
  • High‑dose niacin can affect the liver, blood sugar, and uric acid
  • Never start high‑dose niacin without medical supervision

Most people meet their needs through diet unless they have risk factors.

 

Food Sources of Vitamin B3

Excellent sources include:

  • Chicken, turkey
  • Tuna, salmon
  • Beef, pork
  • Peanuts, sunflower seeds
  • Whole grains
  • Mushrooms
  • Fortified cereals

A balanced diet typically provides sufficient amounts.

 

When to Speak to Your Clinical Team

Contact your NET team if you experience:

  • New or worsening fatigue
  • Persistent diarrhoea
  • Skin changes
  • Cognitive fog
  • Poor appetite
  • Concerns about malabsorption or carcinoid syndrome

They can assess whether Vitamin B3 deficiency is contributing.

 

Key Takeaways

  • Vitamin B3 is essential for energy, DNA repair, and cell health.
  • Carcinoid syndrome can cause deficiency by diverting tryptophan into serotonin, but this is less common today due to modern treatments.
  • Malabsorption and SSAs can also contribute.
  • Symptoms are non‑specific, so clinical assessment is important.
  • Supplementation should be supervised.
  • A varied diet usually provides adequate B3.
  • NET‑Specific Evidence: The NET‑related mechanisms described in this Spotlight (pancreatic insufficiency, bile acid loss, somatostatin analogue effects, steatorrhoea, and liver involvement) are supported by the 2025 ESMO review on nutritional and micronutrient considerations in neuroendocrine neoplasms.  ESMO’s observations show that patients with NETs frequently have fat-soluble vitamins (ADEK) deficiencies and deficiencies of vitamin B3 and B12 that can be successfully supplemented. As long-term deficiencies in fat-soluble vitamins and vitamins B12 and B3 can cause severe symptoms, repetitive evaluation of the status of vitamins A, D, E, K, B3, and B12 and supplementation of deficiencies is recommended in patients with NETs.  Citation  at Reference 3 below.

Personal note

Always speak to your specialist before taking vitamin and mineral supplements — you may not need them if your levels are normal.  Many NET patients assume Vitamin and Mineral deficiencies are inevitable, but with proper monitoring and management (including PERT where appropriate), levels can remain stable. A warning on taking vitamins and minerals generally.  I very often see patients discussing this on my public pages and in my private group.  I just wanted to say that you must always take advice from a professional, just because one patient takes a vitamin ‘x’ or mineral ‘y’, that does not mean you should take it too. 

References Used

  1. NHS Vitamin B3 Guidance
  2. NIH Office of Dietary Supplements – Vitamin B3 Fact Sheet
  3. ESMO – Reducing deficiencies of fat-soluble vitamins, vitamin B12, and vitamin B3 in patients with neuroendocrine tumors treated with somatostatin analogues – L.D. de Hosson, S. Bunskoek, J. Stelwagen, B. Sijtema, S. Huitema, M. van Faassen, G.H. de Bock, D.J.A. de Groot, M.J.E. Campmans-Kuijpers, I.P. Kema, E.G.E. de Vries, A.M.E. Walenkamp, Volume 4, 2025, 100032, ISSN 3050-4619, https://doi.org/10.1016/j.esmorc.2025.100032. (https://www.sciencedirect.com/science/article/pii/S3050461925000310)


Thanks for reading

See also Vitamin B12 – click here

See also Vitamin B9 – click here


See the fat soluble vitamin series below


Vitamin A – click here

Vitamin D – click here

Vitamin E – click here

Vitamin K – click here



Ronny


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.


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Thanks for reading.

Ronny

 

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CategoriesA Spotlight on Vitamins & Minerals Diet and Nutrition Patient Advocacy
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By Ronny Allan

Ronny Allan is a 3 x award-winning accredited patient leader advocating internationally for Neuroendocrine Cancer and all other cancer patients generally. Check out his Social Media accounts including Facebook, BlueSky, WhatsApp, Instagram and and X.

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