Too much sun or not enough? How to get the balance right

Woman in sun hat
‘It might just be that wealth is both the reason that people get more sun and that they are healthier.’ Photograph: Photo by Terry Sebastian/Getty Images/Flickr Open

Beaches are one of the truest pleasures our world has to offer. There’s nothing quite like spending the day baking in the sun with the cool ocean just a few metres away. It’s bliss.

That is, of course, until you get sunburnt.

The sun is the source of a strange dichotomy. On the one hand, it’s the source of all life on Earth, and the main reason that ice cream is a delightful experience. On the other, spending too much time out in the sun not only causes painful burns, it causes cancer too.

But, despite the cancer risks associated with too much of it, there are increasingly calls for us to be spending more time in the sun, without protection from sunscreen. Apparently it increases life expectancy, reduces the risk of high blood pressure, reduces the risk of cancer (yes, you read that right), improves sleep, and a whole host of other claims.

Unfortunately, the truth is far more complex than that. Extended hours in the sun are probably still not that good for you after all.

Sensational sunlight

Most of these claims come from a collection of large epidemiological studies, which looked at people who spent time in the sun, and compared them with those who spent more time indoors. What they found is that people who self-report more sun exposure were also healthier in a surprising number of ways – they had lower blood pressure, less risk of heart disease generally, less prostate cancer, and were less at risk of dying overall.

This came as something of a surprise to many scientists. It’s very well-demonstrated that sun exposure is the main source of skin cancer – somewhere between 95 and 99% of all skin cancers are attributable to exposure to the sun.

Cancer is generally considered to be bad, medically speaking.

The thing is, most skin cancers are relatively harmless. Melanoma – the deadliest form of skin cancer – makes up just 2% to 3% of all cases. The remaining 97%, while obviously still bad for you, are much less risky. In Australia in 2011, about 11,000 people were diagnosed with melanoma and over 1,500 died of the disease. Conversely, more than 400,000 people were diagnosed with non-melanoma skin cancers, but these only caused about 500 deaths.

There’s also vitamin D to consider. We need sunlight to make vitamin D, so more sun exposure equals more vitamin D equals better health, presumably.

It might just be that wealth is both the reason that people get more sun and that they are healthier

This is where the conundrum comes in. Sun exposure causes cancer, but often those cancers are treatable. There’s also evidence that not getting enough sun might be harmful to your health, reducing your blood levels of vitamin D and increasing your risk of any number of diseases.

But before you run headfirst into the midday blaze, there are some issues that make sunlight a bit less rosy.

Rich people ruin everything

The main problem with the idea that lots of sun is good for us basically comes down to rich people.

Let me explain.

In the studies of sun exposure that found that more sun was better for health, the people who got more sun were also different to dark-dwellers in many other ways. They earned more, were less likely to be obese, had fewer chronic diseases, were better educated, and generally were much healthier than their indoor counterparts. This is a problem when we’re talking about health outcomes, because we know that being wealthier – or, more technically, less socio-economically deprived – is associated with much better health.

So it’s possible that what is causing people to be healthier in these experiments is not the sunlight, but a range of other socioeconomic factors that we know are good for health. This is what’s known as confounding, and it’s a real issue in population studies of this type. We can factor this in, using complex statistical inference models, for the things that we know about, but there’s always the possibility that the things we don’t know about are getting in the way.

It might just be that wealth is both the reason that people get more sun and that they are healthier.

Sunlight worldwide

There are other issues with the argument that more sun is better. It’s important, when we’re talking sun exposure, to remember that it’s not a fixed value. The most common way of measuring potential sun damage – the UV index – changes from day to day, season to season, and varies wildly depending on where you are in the world. The UV index for Sydney, Australia in midsummer varies from 11 (extreme UV) to 14 (very extreme UV), and can cause serious skin damage in under 10 minutes. Conversely, the UV index in Stockholm, Sweden – where much of the sun exposure research was done – is almost always at 6 or below. For most of the year it takes four hours to get as much sun in Sweden as you get in 15 minutes in Sydney.

These are very large differences.

There are also questions about skin colour. People who have darker skin are less likely to experience skin cancers, making the sun a bit safer for them, but they are also not well-represented in the research that finds sun exposure to be healthier, so it’s hard to reference the benefits of the sun as well.

Some people are also concerned not about the sun, but about the protection: sunscreen. People are concerned that the “slop” part of the Australian Cancer Council’s famous slogan might be contributing to a number of diseases, although it’s worth remembering that sunscreens are tightly regulated and tested for safety and efficacy. There may be environmental pollutants associated with sunscreens, but the current best evidence that we have indicates that mostly they just cause transient skin rashes.

So is sunlight good for your health?

Well, yes. Definitely. It’s almost certain that getting a bit of sun improves your physical wellbeing. The question really is how much, because the exact amount is extremely hard to determine. The Cancer Council of Australia has detailed, scientifically-supported recommendations that basically boil down to getting more sun in winter, when the UV is low, and staying out of the sun as much as possible in spring, autumn, and summer, when the UV varies between high and very extreme.

Ultimately, it’s all very variable, and incredibly complex. If you’re a white-skinned person living in Perth, chances are you should cover up outside. If you’re a dark-skinned person living in Reykjavik, it might not hurt to spend a few more hours outdoors.

The best thing to do if you’re worried is to talk to your doctor, and maybe see a dermatologist. There may be benefits to sun exposure, but there are definitely harms, so before you take any action it’s best to see a medical professional.

The sun might be good for us, but it’s also definitely bad. I know I’ll be slip, slap, and slopping at the beach this summer.

• Gideon Meyerowitz-Katz is an epidemiologist working in chronic disease