Zinc Benefits – What Is Zinc Good For?
Zinc Benefits: What Is Zinc Good For? A dietitian's guide to what zinc does for the body, how much you need each day, and the everyday foods and meals that…
Vitamin D and Cancer Treatment
Why it matters, why deficiency is so common in the UK, and how to advocate for testing.
If you’re going through cancer treatment — or rebuilding your health afterwards — vitamin D is one of the most overlooked foundations of recovery.
- Not glamorous.
- Not complicated.
- But quietly powerful.
Many of the men and women I support arrive feeling exhausted, inflamed, achy, anxious about bone strength, or struggling with immune resilience — and vitamin D deficiency is frequently part of the picture.
This isn’t about “fixing everything with a supplement.”
It’s about strengthening the body that’s already working incredibly hard for you.
Why Vitamin D Matters During & After Cancer Treatment
Vitamin D isn’t just a “bone vitamin.”
It behaves like a hormone and supports multiple systems under strain during cancer treatment.
1. Immune regulation
Chemotherapy, radiotherapy, immunotherapy and hormone therapies all influence immune behaviour. Vitamin D helps maintain balance — not too reactive, not to suppressed.
2. Muscle strength & fall prevention
Cancer fatigue + muscle loss is common. Adequate vitamin D improves muscle function and reduces fall and fracture risk.
3. Bone health
Androgen Deprivation Therapy (ADT), aromatase inhibitors, steroids and malabsorption all weaken bones. Vitamin D supports calcium absorption and bone repair.
4. Gut health
Anyone with diarrhoea, bile acid malabsorption, pancreatic insufficiency or resections is at risk of vitamin D malabsorption.
5. Mood & cognitive support
Low vitamin D is associated with low mood, low resilience, and mental fog — all things that compound the emotional weight of cancer recovery.
Why Vitamin D Deficiency Is So Common in the UK
- No vitamin D is produced (via your skin) from October–April – The UK sun is simply too weak.
- Most adults don’t achieve adequate summer exposure – 10–20 minutes on arms and legs at the right UV index is less frequent than we imagine.
- Darker skin tones need more UV exposure – Melanin reduces vitamin D synthesis.
- Gut issues reduce absorption – Coeliac disease, pancreatic insufficiency, chronic diarrhoea, Crohn’s, bile acid malabsorption, and cancer-related GI changes all reduce vitamin D uptake.
- Older adults naturally make less – Production declines with age, making deficiency even more likely.
How to Ask Your GP for a Vitamin D Test
You’re fully entitled to ask — especially during or after cancer treatment.
Ask for a 25-hydroxyvitamin D (25-OH-D) blood test. A clear script you can use:“
Could I please have my vitamin D level checked? I’m undergoing/have undergone cancer treatment and I’m experiencing fatigue/muscle weakness/bone aches/gut issues. Vitamin D is essential for immune, bone and muscle health.”
Mentioning ADT, aromatase inhibitors, malabsorption or chronic diarrhoea strengthens the clinical justification.
If Your GP Refuses Testing
(Unfortunately, this does happen).
This is usually due to cost-saving policies, not medical disagreement.
Here’s how to handle it:
1. Ask for the refusal to be recorded in your notes
This often prompts reconsideration.
2. Use a private test
Choose an accredited UK laboratory (UKAS or NHS labs).
3. Begin safe supplementation
Most adults benefit from 400-1,000 IU (10-25 mcg) per day year-round unless instructed otherwise.
This is not medical advice to mega-dose.
It’s about safe, evidence-based maintenance.
Can You Take Too Much Vitamin D?
Yes, and here’s why it matters.
Vitamin D is essential, but more is not better. Most problems occur when people take very high doses for long periods without checking their blood levels — often because of misinformation online.
What Too Much Vitamin D Does
Excess vitamin D raises blood calcium (hypercalcaemia), causing:
- Extreme thirst
- Peeing frequently
- Nausea & vomiting
- Abdominal pain
- Constipation
- Confusion
- Irritability or fog
- Muscle weakness
- Heart rhythm changes
- Kidney stones
- Kidney damage in severe cases
Symptoms typically appear after weeks to months of high-dose use.
What Counts as “Too Much”?
In adults:
Up to 4,000 IU (100 mcg) daily = safe upper limit – Toxicity typically involves 10,000 IU (250 mcg) daily or more, taken long-term.
Very high “loading doses” should only be used with medical supervision and follow-up testing.
Vitamin D is fat-soluble, so it accumulates, particularly in people with lower body weight or impaired kidney function.
Who Is More at Risk?
- Those taking multiple supplements containing vitamin D
- Anyone on high-dose prescriptions that were never reviewed
- Those following high-dose online “protocols”
- People with kidney disease, sarcoidosis or hyperparathyroidism
Supplement Safety
For most UK adults — including cancer survivors — a simple, safe plan is:
- 400–1,000 IU (10-25 mcg) daily year-round
- Re-test after 3 months
- Increase only with supervision
- Maintain good calcium and magnesium intake to support utilisation
If you’re already taking more than 4,000 IU daily, get your vitamin D, calcium and kidney function checked.
What Happens If Vitamin D Deficiency Is Left Untreated?
Short term:
- Fatigue
- Mood changes
- Muscle weakness
- Lower immunity
- Increased infections
- Poor recovery from treatment
- Low calcium
- Worsening diarrhoea for some people
Long-term:
- Osteoporosis
- Fractures
- Reduced treatment resilience
- Impaired immunity
- Deterioration in quality of life
This isn’t about blame — it’s about giving your body what it needs to repair, stabilise and thrive.
Your Next Steps – A simple, safe, UK-friendly plan
1. Get tested if you can
Ideal range: 75–150 nmol/L
2. Supplement consistently
Most people need daily vitamin D in the UK, even in summer.
3. Re-test after 3 months
Adjust your dose accordingly.
4. Pair vitamin D with other foundations