The importance of vitamin D used to be linked only with calcium for bone health. But research shows us that it is involved in many other aspects of our health. Today we’ll look at how knowing our Vitamin D level is important in relation to cancer.

What is Vitamin D?

Vitamin D (vit D) is unlike most other vitamins. Your body can make its own vit D when you are exposed to sunlight – and hence it is often called the ‘sunshine vitamin.’ Our body cannot make other vitamins, so we need to get them from food. But what is most interesting is that your body can turn vitamin D (also known as cholecalciferol) into a hormone. The majority of this conversion happens in the kidneys. This hormone is often called “activated Vitamin D” or “calcitriol.” You might also see this referred to as 1,25-dihydroxyvitamin D3 or 1,25(OH)2D. 

So unlike other vitamins,  getting adequate vit D doesn’t depend on eating certain foods (although there are low levels in some foods such as cod liver oil, eggs). Rather you need to expose your skin to sunlight regularly and/or take vitamin D supplements.

Why is it important to look at Vitamin D?

Vit D has numerous actions in the body, many of which can relate to cancer, including involvement in:

  • bone strength – and might protect from bone metastasis
  • immune modulation
  • endothelium function (endothelium lines the insides of blood and lymph vessels)
  • initiating factor in coagulation (see last week’s post)
  • estrogen levels – it is an aromatase inhibitor so can reduce estrogen levels
  • cell adhesion – involved in metastasis
  • blood sugar regulation
  • gut microbiota
  • induces apoptosis
  • down-regulates growth factors
  • promotes cell differentiation
  • anti-inflammatory – thus involved in many chronic illnesses

What do the studies say about vitamin D deficiency in relation to cancer?

With its functionality in so many different aspects of cancer, it maybe doesn’t come as a surprise that low levels of vit D are seen in more than 3 out of 4 cancer patients. In some studies, over 90% of newly diagnosed cancer patients were severely deficient in vit D, those with the lowest levels having the most advanced forms of cancer.   

When we look at the studies on the prognosis of patients with colorectal, prostate, and breast cancers, the results consistently show that patients with the lowest levels of vit D at or near diagnosis have the worst outcomes.

Vit D levels are also associated with the risk of developing cancer, with studies specifically showing an inverse and concentration-dependent relationship between serum vit D levels and breast cancer risk.

This all points to the fact that, if you have cancer, it is imperative to correct any low vit D levels. And this is good advice for all of us – for the prevention of cancer and other chronic illnesses. 

Do cancer treatments affect Vitamin D levels?

Studies have shown that several different chemotherapy regimens reduced vit D levels in patients. One study [1] looked at breast cancer patients in France who had chemo during the summer time. The findings showed that deficiency in vit D went from 80% of patients before chemo to 97% of patients after chemo! The average vit D levels fell from 21 ng/ml to 14 ng/ml, with a quarter of the patients levels falling below 10 ng/ml.

But is this because people stopped going outside and thus reduced their sunlight exposure as they didn’t feel well, or did the chemotherapy drugs interact with vit D? Or is it that the body utilized the vit D – with a higher rate of the hormone version produced for its anti-cancer effects? We don’t have the answers to this yet.  

Additionally, other drugs can deplete your vit D levels – a prime example being statins. Another good reason for monitoring our levels. 

Interestingly, vitamin D might help improve the effectiveness of some cancer treatments. Researchers at the Salk Institute showed that the drug Gemcitabine worked 57 % better in pancreatic cancer patients if combined with vitamin D [3].

How to monitor vitamin D

As vitamin D seems to be involved in so many aspects of our health, it is useful to know what our own personal levels are. This knowledge then helps us determine if we need to take a supplement or increase our sun exposure.

You can ask your doctor to test your levels for you, or you can get a home test kit, where you send off a finger prick blood sample to the laboratory. The Vitamin D Council has an in-home kit for $50 but also lists other testing labs on its site that can do the test.  

In the UK, you can get home testing also – and I think the cheapest option is through BetterYou for £28.00. They give you a free spray vitamin D with your results too!

The test is very simple – and don’t worry – the finger prick won’t hurt!

The above tests all measure 25-OH vitamin D, which relates to the body’s stores of vitamin D.

For a minority of people, it may be worth asking your doctor to also test you for the metabolite of 25-OH vitamin D, namely the 1,25-dihydroxyvitamin D – the active form.  This can be important for people with hypercalcemia (too much calcium in the blood) or decreased kidney function (on dialysis, or kidney disease). If you are unable to get your vitamin D within optimal range with supplementation, this might be another reason to run the additional 1,25 vit D test. For the rest of us, the regular 25-OH Vit D test alone is sufficient. 

We should all have an annual vit D blood test. If your levels are low, repeat your test 2-3 months after you begin a supplementation program to check that your levels are increasing. 

What levels are optimum?

You’d think this would be an easy question – but when you look at what different groups say, there is a huge variation. The main reason for this is that some organizations recommend levels based solely on vitamin D’s bone health function.  Their recommendations do not take into consideration the effect that higher dose levels have on other systems in the body. For more on this, see my previous blog post on Breast cancer and vitamin D.

The optimal serum level of 25(OH) vitamin D for cancer and other health benefits is now considered to be 55-80 ng/mL.

Who is at higher risk of vitamin D deficiency

People at higher risk of vitamin D deficiency are those who have:

  • limited amount of sun exposure or always use sunscreen
  • obesity
  • dark skin pigmentation
  • gut disorders preventing absorption of dietary fats/vitamin D
  • polymorphisms for vitamin D receptors
  • gall bladder removed or gall bladder dysfunction
  • people who live in northern latitudes

What should I do if I am deficient

After receiving your vitamin D test result, you’ll want to take action so that you can maintain your levels in the optimal range, namely 55-80 ng/mL. There seems to a “sweet spot” for the benefit of vitamin D – so don’t just go for higher and higher levels.  Try to maintain levels in the range. 

If your levels are already in this range – well done. Keep doing what you are doing – spending some time in the sun and maintain any supplementation you taking.

And if you are not in this range, there are two approaches – spending some time in the sun or supplementation.


What was that –  “spending some time in the sun”???

Yes, we still hear about how we should avoid the sun to reduce our skin cancer risk – but from what you have just read, we can now see that avoiding the sun can increase our risk of many other cancers if we are deficient in vit D. We obviously don’t want to burn in the sun, but having brief exposures (without sunscreen) can be beneficial. (If the exposures are long, then yes, wear sunblock, a hat etc., to avoid burning.)

There is clear evidence from a number of studies that people who have regular exposure to the sun get less cancers. In relation to the fear of skin cancers, a study at the University of New Mexico found that people with high exposure to sun are less likely to die from melanoma (a type of skin cancer) [2]. 

Our skin makes vitamin D when exposed to a “pinking” dose of sunlight. The amount you make depends on several factors including your age, how much skin is uncovered, your skin tone, and if you have polymorphisms related to vitamin D receptors. Without sunblock and with arms and legs exposed, our skin can make, on average, 10,000 to 15,000 units of vitamin D in one pinking sun exposure. Sunblock with an SPF of more than 15 blocks 100% of the vitamin D production by the skin. 

And remember, there are other benefits to spending time in the sun – as the photo at the top of the page suggests – like fun in the sun, relaxation, that feeling of warmth on the skin……


If you don’t spend much time outdoors and your test results revealed low vitamin D levels, you should consider supplementation to get your levels up to the 55-80 ng/mL mark.

The Institute of Functional Medicine recommend the following supplementation doses of vitamin D,  according to your current vitamin D level:

If your level is:        Supplement with:

<10 ng/mL –         10,000 units per day

10–20 ng/mL –     10,000 units per day

20–30 ng/mL –     8,000 units per day

30–40 ng/mL –     5,000 units per day 

40–50 ng/mL –     2,000 units per day

Because everyone produces and metabolizes vitamin D differently, the only way to properly manage vitamin D supplementation is by checking your levels. Vitamin D levels change slowly, so check them 8-12 weeks after starting supplementation. Your body can best absorb vitamin D when you take it with the day’s largest and most fatty meal.

Which supplement?

It is recommended that you take vit D3 as a supplement along with vitamin K2. (However, if you are currently taking warfarin, you shouldn’t take vitamin K2.).

Vitamin D is a fat soluble vitamin, and therefore best taken with a meal containing some fat, or in a fat solubilized form. If you have gall bladder issues or have had your gall bladder removed, or have trouble absorbing fats, take your vitamin D and K with the digestive enzyme lipase so that it can be absorbed. 

Supplements can be in liquid form or capsules and which you choose will depend to some extent on the dose level you need. Here are a couple of suggestions:

 – liquid Vitamin D and K by Thorne Research 10 drops is 5,ooo IU Vitamin D3 and 1mg Vitamin K2 (MK4).

 – capsule Vitamin D and K by Life Extension Foundation 1 capsule is 5,000IU Vitamin D3 and 1100mg K2 (MK4) and 1000mg K2 (MK7). It also contains iodine.

If you take more than one supplement – or if you take a supplement plus a multi-vitamin/mineral – make sure that the combination is not taking levels too high.

Remember to retest your levels after about 2-3 months and you might then be able to reduce your dose level to a lower maintenance dose. 

Take home points

The vast majority of cancer patients are deficient in vitamin D at the time of diagnosis. Those with the lowest levels tend to have the more advanced cancer.

A simple blood test can tell you your levels – tested either through your doctor or using a home finger prick test

When you know your levels, you can then use supplementation or safe sun exposure to optimize them. Retesting, then annual monitoring will ensure your levels are optimized.

This is important because optimized vitamin D levels can help in the prevention and prognosis of cancer.

[1] Jacot W, Pouderoux S, Thezenas S, et al. (2012). Increased prevalence of vitamin D insufficiency in patients with breast cancer after neoadjuvant chemotherapy. Breast Cancer Res Treat. 2012, 134(2), 709-17.

[2] Berwick, M., Armstrong, B., Ben-Porat, L. et al., (2005). Sun exposure and mortality from melanoma. JNCI J Natl Cancer Inst (2005) 97(3): 195-199.doi: 10.1093/jnci/dji019


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