Neuroendocrine Tumours (NETs) – Vitamin K (Phylloquinone / Menaquinones)

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.

1. What Is Vitamin K?

Vitamin K is a fat‑soluble vitamin essential for:

Normal blood clotting
Bone health
Vascular health

Two main forms:

Vitamin K1 (phylloquinone)
Vitamin K2 (menaquinones; MK‑7 and MK‑4)

2. Why Vitamin K Matters for NET Patients

NET patients may be more vulnerable to low Vitamin K because of:

Malabsorption
Pancreatic insufficiency
Small bowel resections
Chronic diarrhoea / bile acid malabsorption
Somatostatin analogues (indirect effect via fat malabsorption)

🟪 Why Liver Involvement Matters for Vitamin K

The liver uses Vitamin K to activate clotting factors (II, VII, IX, X). If the liver is affected by metastases or disease:

clotting factor activation becomes less efficient
Vitamin K recycling slows
INR may rise
this can mimic Vitamin K deficiency, even when intake is normal

Vitamin K doesn’t clot blood — the liver does. If the liver is compromised, Vitamin K pathways are compromised too.

🟪 What About Chemotherapy? Does It Affect Vitamin K?

Chemotherapy does not directly cause Vitamin K deficiency. However, some of its side‑effects can indirectly reduce Vitamin K absorption or activation:

Chemotherapy‑related diarrhoea
Gut inflammation / mucositis
Prolonged antibiotics during neutropenia
Liver involvement (common in NEC)

Somatostatin analogues (octreotide / lanreotide)

These have a predictable, chronic effect on fat absorption → reduced absorption of all fat‑soluble vitamins, including Vitamin K.

SSAs = predictable low‑grade Vitamin K risk Chemotherapy = indirect, situational risk

3. Why Vitamin K Isn’t Usually Tested (Even When A, D, and E Are)

Vitamin K is not routinely tested because blood levels do not reflect functional status. Vitamin K is rapidly cleared from the blood, so a blood level normally only reflects what you ate in the last 24 to 48 hours, not long-term storage or tissue sufficiency.

However, functional tests exist:

PIVKA‑II
Undercarboxylated osteocalcin

…but they are not widely available, normally only found in research/specialisation use, hight in cost and lack standardisation.

Thus why clinicians normally infer Vitamin K status from clotting tests such as Prothrombin Time Test and INR (PT/INR). NET patients at risk of malabsorption, pancreatic insufficiency, bile acid loss, long term use of somatostatin analogues (SSAs), liver involvement…….all make Vitamin K deficiency more plausible if a clotting abnormality appears.

4. Symptoms of Vitamin K Deficiency

Easy bruising
Nosebleeds
Bleeding gums
Heavy menstrual bleeding
Prolonged bleeding from cuts
Elevated INR

🟪 A Quick Note About INR

INR is not a Vitamin K test. It only becomes abnormal in significant deficiency and is not specific.

5. Testing Vitamin K Status

Because direct testing is unreliable, clinicians use:

PT/INR — detects significant deficiency
PIVKA‑II — specialised
Undercarboxylated osteocalcin — research use

6. Dietary Sources of Vitamin K

K1: spinach, kale, broccoli, cabbage, herbs K2: natto, cheese, egg yolks, meat, fermented foods

7. Supplements: What NET Patients Should Know

Forms:

K1
K2 MK‑7
K2 MK‑4

Evidence:

Strong: clotting
Moderate: bone health
Emerging: vascular calcification
No evidence: tumour suppression or detox claims

NET‑specific cautions:

Warfarin users must not change Vitamin K intake without supervision
Malabsorption patients may need supplementation — but only after testing

🟪 K1 vs K2 — Why Choose One Over the Other?

Vitamin K1

Primary dietary form
Used directly for clotting
Included in most multivitamins

Best for: general nutritional support and malabsorption replacement.

Vitamin K2 (especially MK‑7)

Longer half‑life
More active in bone and vascular tissues
Often paired with Vitamin D3

Best for: bone strength and vascular calcification pathways.

K1 = standard form for clotting K2 (MK‑7) = longer‑acting, bone + vascular focus Both are safe — the choice depends on the goal.

8. Interactions

Warfarin — major interaction
Antibiotics — reduce gut‑derived K2
Bile acid sequestrants — reduce absorption
Orlistat — reduces fat‑soluble vitamin absorption
High‑dose Vitamin E — antagonises Vitamin K at pharmacological doses

9. Can You Take Too Much Vitamin K?

Vitamin K1 and K2 have no known toxicity, even at supplemental levels. The only form associated with toxicity is Vitamin K3 (menadione) — not used in human supplements.

OTC Vitamin K supplements (K1 and K2) are safe. The only caution is for people on warfarin.

10. Vitamin D + Vitamin K: How They Work Together

Vitamin D3 increases calcium absorption
Vitamin K2 activates proteins that use calcium safely in bone and vascular tissues

Bone: D3 brings calcium in → K2 locks it into bone Vascular: K2 prevents calcium depositing in arteries

This synergy is specifically D3 + K2 (usually MK‑7), not D3 + K1.

11. Key Takeaways for NET Patients

Vitamin K is essential for clotting and bone/vascular health
NET patients with malabsorption or liver involvement are at higher risk
Vitamin K testing is unreliable — this is normal
K1 and K2 are both safe; choice depends on the goal
Only major caution is warfarin
Vitamin K issues are mainly a GEP‑NET topic — especially small intestine and pancreatic NETs — with lung/thymic NETs and poorly differentiated Neuroendocrine Carcinomas affected mainly if liver metastases are present

Thanks for reading

See also Vitamin B12 – 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.