Sun and Cancer

Cancer Warning! Why you may need more sun.

The Sun-Cancer risk

We’ve all seen it everywhere. To reduce your cancer risk, you have to avoid the sun, cover yourself as much as possible, use sun cream every time you go in the sun, etc.

And yes, exposing yourself abruptly to strong sunshine when you spend the rest of the year within closed doors and covered with clothes is a very bad idea. Your skin hasn’t had the time to build any defences and you will burn. This will damage your skin on a cellular level and could be a contributing factor to cancer. (source)

And yet, this really doesn’t feel natural. So what is a reasonable and balanced view on sunshine and cancer?

The ancestral perspective.

We were born naked sons and daughter of Africa. Unlike most mammals who live on land, humans don’t have fur to protect from the sun (or from the cold), so we were left with only our skin to protect us from the scorching rays of sunshine in the land of our forefathers – much like the elephants. We are not cave dwellers, nor are we nocturnal animals either (as indicated by the fact that our primary sense is vision. Other cave dwellers & night animals will rely primarily on hearing or smelling).  

To think that evolution removed our fur and didn’t give us any way to deal with sunshine is pure nonsense. Evolution – survival of the fittest! – would have eliminated us long before we invented clothing.

Our skin is our sun protection

What is real though, is that we have different skin colours based on our ancestry and the latitude our forefather lived at. Our dark skins would have protected us from the intense light on the equator and the tropics, and our white skins would have made it possible for us to absorb enough sunlight in the regions closer to the poles. On the opposite, a dark-skinned individual would be more at risk from vitamin D deficiency away from the equator (as rickets cases do actually show in northern countries), and a clear-skinned individual would struggle to live the hunter-gatherer way in tropical & equatorial countries (and will be at high risk of getting skin cancer – Source).

Sun & Cancer prevention

Getting some sunshine on our skin has several very important benefits for us. It has a proven effect on mood, curbs hunger, normalises the body daily rhythm, may lower blood pressure, promotes good vision, etc.

But perhaps the most significant effect of sunshine is that of creating vitamin D. In the presence of sunshine, our skin converts a molecule closely related to cholesterol into vitamin D3. Vitamin D3 is then, in turn, converted with the help of the liver and the kidneys into the active version of Vitamin D (called 1,25-dihydroxycholecalciferol). It is now thought that Vitamin D acts more like a hormone than a vitamin, with many very important roles in the body. Vitamin D is involved in calcium metabolism and absorption, and in bone growth.

The importance of Vitamin D in the case of cancer has at least three elements:

  • Immune system: It is now clear that vitamin D has an important role on the immune system. In fact, the cells of the immune system present vit. D receptors (if the vitamin was a key, the receptor would be the keyhole). Supplements of vitamin D has been used with positive results in the case of tuberculosis, influenza and some viral infections (study, study). Vitamin D also has an antimicrobial action (study) and is crucial to activating the immune system (study).
  • Vitamin D has been shown to be involved in cell proliferation, differentiation and apoptosis (study). So much so that it has been theorised (but not yet proven) that vitamin D could be used as an additional chemotherapy agent to help cancer cell differentiates and stop their malignancies (study).
  • Vitamin D is also capable to inhibit the inflammatory cascade (study), and in particular the inflammatory processes involved in cancer progression, including cytokines, prostaglandins, MAP kinase phosphatase 5 (MKP5) and the nuclear factor kappa B (NF-κB) pathway (study)

In addition, many studies have correlated low vitamin D and cancer risk and progression. This has been shown in studies after studies, after more studies (also here and here). And although the science is too early to be able to claim vitamin D has a curative role in cancer, it certainly warrants further investigation through larger randomised trials.

There are also concerns that the sun cream itself might be harmful and contributing to cancer risk (source), and there are debates as to whether it is even possible to demonstrate that a sun cream help prevents cancer (source). One of the issue scientists run into is that it’s unethical to do experiments testing the effectiveness of sunscreen by randomly assigning some people to use it and others to skip it.

Vitamin D as a complementary cancer therapy

But the benefits of sunshine and vitamin D in cancer care isn’t limited to prevention & potential effect on the disease. There are other points that need to be considered, such as

For surgery

A 2015 systematic review (study) of vitamin D status and surgical outcome (not related specifically to cancer) concluded that 26 of the 31 studies included in the review report at least one statistically significant worse outcome in patients with low vitamin D status – in other words, not having sufficient vitamin D could lead to complications after surgery.

After chemotherapy

A few, small-scale studies have indicated a possible fall in vitamin D levels during chemotherapy (study, study). The subject is not well understood and warrants better scientific research. At this stage I haven’t found compelling evidence yet as to non-interaction between vitamin D and chemotherapy, and it would seem that some chemotherapy agents are made more effective when combined with vitamin D (always check with your oncologist! – study). It does also strongly suggest that vitamin D levels need to be checked and corrected once the patient is in remission.


In a few small papers, Vitamin D has been shown to help protect some cells against radiation damage (study, study) and its deficiency has been associated with increased local radiation-induced inflammation (study). It is recommended to avoid vitamin D during radiotherapy as it may interfere with the treatment, however it may be part of a remission programme.

Why Vitamin D supplement shouldn’t be first line for cancer protection

Unfortunately, the vitamin D supplement drumbeat has been somewhat excessive in some health circles, and some people have been overdoing it. Pill pushers with a careless attitude have been selling vitamin D megadose supplements (it is possible to find 50,000-IU supplements, which could lead to toxicity if used for several months).

Vitamin D supplements can lead to toxicity

Overdosing on Vitamin D is not a good idea. It will disrupt your body calcium metabolism, take the calcium out of the bones and put it in the blood. There is a tendency that the calcium will then accumulate in non-physiological places (arteries?), and some people have ended with kidney damage, severe back and joint pain, brittle bones, and cardiovascular symptoms (source). Do not supplement blindly! Vitamin D toxicity is a real thing.

On the other hand, it is virtually impossible to overdose vitamin D by sun exposure alone, because your body will regulate its secretion to the level that it really needs. So it takes the guesswork and the testing out.

What to do for best Vitamin D status?

From what we’ve been discussing, it is obvious that the best way to get adequate vitamin D is to let your body make some from the sun. And while there is some debate as to how much sun is required, it is clear that 10 minutes a day while wearing long trousers and sleeves isn’t going to suffice. This chart here is very helpful to get some idea of the complexity of the matter. In summary:

  • Response from sunshine varies by up to a factor 4 from individuals to individuals
  • It depends on your activity
  • It depends on your position (lying down is more effective)
  • It depends on whether you are overweight or not
  • It depends on whether the sky is obscured by air pollution and/or clouds
  • Obviously it depends on the amount of clothing you wear
  • Obviously it depends on where you are in the world and what your skin colour is

So depending on all of those factors, the answer could be from 20 minutes up to almost the whole day. And none of those have fully factored in the sun protection aspect.

When it comes to protection against sun exposure, there are two radically different approach

  1. Allow your body to develop the protection it needs to deal with the sun. This is something that needs to be done gradually. Let me say this once again: if you’re fair-skinned and stay indoors much of the year, you just can’t expect to go naked on a Mediterranean beach holiday and be fine. You need to start exposing your body from spring time – at that time the side of the earth you’re on will be further away from the sun and the sunshine will have a longer optical path through the atmosphere to reach you, which mean you will need to spend longer outside to get the same amount of vitamin D. You will slowly develop a tan which will give you protection against summer sun. And as you do, and as your skin will progressively turn darker, it will become less efficient at producing vitamin D, which means that you will have to spend a little longer outside. Then, as the summer comes your skin will be ready for the harsher UV light. Always, always expose yourself to a sun that is appropriate to your skin tone – the clue to finding out is by looking at where your ancestry comes from, and use this as a reference. If your ancestors came from closer to the poles, use adequate caution. If closer from the equator, you will need longer sun exposure. If you have mixed ancestry, it will be somewhere in between.
  2. Alternatively you could provide the protection for your body. This is a legitimate strategy when you live outside of your skin bioregion (i.e. closer to the equator than what your ancestry evolved to adapt to). Example would be someone of European/Caucasian origin living in the tropics. This is also the way to go if you have to spend a lot of time indoors during the rest of the year, and for the parts of your body you don’t get to expose to the sun on a regular basis.

Also remember, when it comes to winter sports, ice and snow reflect UV light very well, and in the mountains there is less depth of atmosphere to absorb UVBs. So although it may be winter, you could get exposed to a large dose of sun very rapidly. If you have lost your tan by then, please use sun cream…

Another important point to keep in mind, is that vitamin A, D and K2 work synergistically (study), so it is important to keep your vitamins A (as retinol) and K2 up at the same time. The highest concentration of both can be found in liver of any animal (including fishes, so cod liver oil is a good source). An alternative for dairy-free ovo-vegetarian is eggs, of course. Many vegetables are said to contain either vitamin A and/or K, however they only contain the precursors of such vitamins, and the conversion to the active form varies widely from person to person.

Why you may need more sun to avoid cancer

Leave a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.