In the last post, we talked about the new report on vitamin D and cancer from the International Agency for Research into Cancer (IARC). In this one, we’ll summarise what the report has to say on the balance between getting enough vitamin D through sun exposure and reducing the risk of skin cancer by being SunSmart.

First, a quick recap:

  • Our skin makes vitamin D when exposed to sunlight, which is the major source of this chemical.
  • BUT too much exposure to the sun can cause skin cancer.
  • Having enough vitamin D is essential for healthy bones, among other things.
  • There is growing evidence that bowel cancer is less common in people who get enough vitamin D, but the jury’s still out for other types of cancer.

So the big question is: do vitamin D’s benefits mean that staying safe in the sun will actually do more harm than good? Should people be actively trying to tan for the sake of their health? The answer, according to the new IARC report, seems to be no.

Vitamin D and sun exposure – casual exposures are enough for most people

There is no doubt that vitamin D is important but we need to work out the safest way to increase someone’s vitamin D levels. Encouraging them to spend more time in the sun is unlikely to be the right approach for several reasons, (unless they currently get very little exposure either through dress or not going out of doors when UVB is around).

For a start, the link between skin cancer and ultraviolet radiation from the sun is “well-established” and the rates of this cancer are still on the rise.

Our skin’s ability to create vitamin D peaks after a relatively short burst of UVB, and is always less sunlight than the amount that causes reddening or burning. This is important, and actually very reassuring – it means that, amid all the confusion about sun and vitamin D, the main thing to do is to get some sun exposure, but avoid sunburn. By doing so, it’s possible for everyone to reap the benefits of vitamin D without incurring the risk of skin cancer.

Our skin’s ability to make vitamin D isn’t infinite either. It has a natural cut-off point, to prevent toxic levels from building up, so after a brief amount of UV exposure, extra sunlight does no good.

The report says that light-skinned people reach this point after 5-10 minutes. Beyond that, soaking up more sunlight will not increase vitamin D levels, but will increase the risk of skin cancer. As the report says, “for children and adults, everyday casual exposure to sunlight provides [enough] vitamin D.” But of course, there are so many variables that it’s virtually impossible to make useful estimates of actual times for individuals.

Vitamin D and supplements

IARC say that vitamin D supplements would probably represent the safest way of increasing your levels of this chemical. But they don’t recommend that people actually take these supplements. Why?

We don’t actually know what would happen if you gave well-fed healthy people high doses of oral vitamin D and kept it up for several years. According to the report, it’s “practically never been studied”. Most studies have been limited to weeks or months. They also tended to look at young, healthy people who are most likely to tolerate high doses of vitamin D, rather than elderly people who have the greatest need for it.

On the surface, this seems like unnecessary nit-picking, but IARC is justified in its concern. Sadly, experience has taught cancer scientists to be very cautious when it comes to prescribing vitamin or mineral supplements.

Many studies in the past have found that high doses of vitamin supplements – from beta-carotene to selenium to vitamin E – could actually do more harm than good. While lab studies suggested that they would be beneficial, clinical trials found that they either had no effect or could even increase the risk of cancer and other chronic diseases. And some studies have found that people with very high levels of vitamin D could be just as detrimental as very low levels.


IARC calls for more trials to really pin down the effects of vitamin D supplements – either positive or negative – depending on how much vitamin D people already have in their system.

Until then, they feel that there is no solid basis for changing any existing recommendations about vitamin D.

As such, Cancer Research UK’s line remains the same. Vitamin D is important, but you should be able to make enough through casual, ‘everyday’ sun exposures, and certainly before the point at which your skin starts to redden or burn. Trying to get enough of this vitamin shouldn’t stop you from taking steps to avoid sunburn and protect yourself against skin cancer.