Sun Awareness: Should we rip up the rule book and start again?

I am a fully paid up, matriculated, accredited and long-standing member of the dermatology community, but I have a horrible feeling that my tribe has gone horribly wrong in what we tell the public about sunlight. To be specific, I think our advice to avoid sunlight is wrong. 

We need to step back and stop thinking narrowly about photo-aging and possible skin cancer and remember that we are doctors before we are dermatologists, and that reduction in all-cause deaths trumps everything. As clinicians, we spend our professional lives, consciously or unconsciously calculating risk-benefit ratios.  When I prescribe a treatment to my patients, I talk about the risk (the side effect profile) and the benefits (alleviation of the disease I am treating).  Sadly, dermatologists have never viewed sunlight in this way: they overstated the risks, and failed to consider the benefits. This needs to change.

UV advice: Wardie Bay is not Bondi Beach.

Current guidance on sunlight exposure is lifted, largely unaltered, from that developed in Australia in the 1970s and 1980s. The more observant Edinburgh readers of this piece will have noted that Wardie Bay (located on the exposed East Coast of Scotland), much as I love it, is not Bondi beach. Yet, we are advised to slip, slap, slop and avoid the sun between 11am and 3pm in just the same way as Australian surfers and Jackeroos.   

The burning (and DNA damaging) propensity of sunlight is described using the UV Index. The spectrum and intensity of sunlight varies dependent on latitude and season, as shorter wavelength solar radiation is preferentially filtered out by the atmosphere. When the sun is low in sky and thus reaching us through a greater thickness of atmosphere, not only is the overall energy lower, but the spectrum we receive is completely altered as shorter wavelength UV is absorbed, such that no UVB reaches the UK for the 6 months around the winter solstice. 

Shorter wavelengths of UV have greater biological effects; most readily seen as the ability to cause sunburn, but also DNA damage, vitamin D synthesis and, independently of vitamin D, blood pressure reduction.  An internationally recognised CIE Erythemal Action Spectrum has been calculated and weights each wavelength for its burning ability. The UV Index uses this spectrum, allowing us to predict how likely the sun is to cause burning and DNA damage in a particular location. 

30 years ago, I had a wonderful year as a medical registrar in Cairns in subtropical Queensland.  In mid-winter, the UV index around noon sunk to its lowest point of 7, rising to 14 in the summer.  Nowhere in contiguous Australia has a mean midday UV index below 7 at any time of year.

The UV Index in Scotland is measured by the Met Office in Glasgow. Last year it reached 7 for about 10 minutes - just after 1pm on 24th June - and that is it. For half the year it hovers around 0 to 2, climbing to a daily midday peak in the 3 to 6 range in the summer months.  Staggeringly, it is considered that the sunlight advice for Australians of Northern European heritage should be applied in our utterly different UV environment.

If sunlight purely caused harm, this would not matter, but research that I have conducted in Edinburgh in parallel with colleagues around the world is showing multiple health benefits to sunlight, which are particularly relevant to us in the darkest, northernmost limits of human habitation in the world. 

Sunlight Health Benefits: Please can we move on from Vitamin D. 

Good public health advice is based on measures that will increase population health and healthy lifespan. High blood pressure increases your risk of having a stroke or heart attack, and blood pressure reduction reduces the risk of having one of these events. Air pollution similarly increases risks of cardiovascular disease. The robust evidence base means that treating high blood pressure is a priority for primary care doctors, and measures such as the introduction of low emission zones in Edinburgh and other cities will reduce the burden of disease caused by air pollution. Colleagues and friends here at the University of Edinburgh (David Webb, Mark Miller and Dave Newby) have been key players in unpicking this science, and it is satisfying to see that work now feeding through to policy that will improve our lives.

Dermatologists are worried about sunlight and skin cancer, but the first question to ask, is whether sunlight exposure shortens life in the same way that hypertension, smoking or air pollution do.

Remarkably, this has not been done until recently, and seems to be something that dermatologists have shied away from. Pelle Lindqvist, an obstetrician at the Karolinska, first looked into this, using the ‘Melanoma in Southern Sweden’ study.  He found that Swedish women who got the most sunlight had reduced all-cause mortality, with an effect size similar to that of smoking - although in the opposite direction^{1 2}. With Chris Dibben and Andrew Stevenson here in Edinburgh, we have looked at data from the UK Biobank (a collection of samples and data from 0.5m people in the UK), and in a paper shortly to be published we also find a significantly reduced all-cause mortality in UK citizens who get more sunlight exposure.  As with Pelle Lindqvist’s study, cardiovascular mortality was most reduced.  Interestingly, there was a trend to increased incidence of melanoma with more sunlight, but no increase in mortality from melanoma.  Mortality from other cancers was reduced; meaning that more people got melanomas but no more people died from it, and in fact fewer people died from other cancers with the increase in sunlight. Observational studies are always at risk of other factors affecting the outcome, but these independent North European studies are both showing the same effect.

If sunlight does reduce cardiovascular and cancer mortality, what could be causing this? What is the mechanism? After streams of negative Vitamin D supplementation studies, and now the huge VITAL study in the USA and ViDa study in New Zealand, I hope we can move on from only considering Vitamin D^{3 4}.

Measured serum vitamin D is a biomarker for sunlight exposure, and as we have known for a century, it prevents rickets. What these studies conclusively show is that supplementation of the general population has no effect on deaths due to heart disease or cancer.  Other mechanisms must be at play. Work which I have carried out shows that the skin contains large stores of nitrogen oxides, which can be photochemically reduced to NO (nitric oxide) on sunlight exposure, and mobilised to the circulation where it lowers blood pressure and, with it, the attendant risks of cardiovascular disease⁵. 

As a result, in the UK population blood pressure is 5.6/3.3 mmHg higher in winter than summer⁶ and consequently there is a 23% rise in cardiovascular mortality⁷.  If you are a male in Scotland, you are 30% more likely to die in a week in January than a week in July⁸.  Hippocrates described this seasonal variation in mortality 2,500 years ago and we are so inured to ‘winter bed crises’ and the regular near collapse of the NHS every January that we accept it unquestioningly.  This does not have to be.

Risks of sunlight: Melanoma overdiagnosis.

The skin cancer that worries dermatologists is melanoma, which sadly kills around 2,000 people per year in the UK. Diagnosing and preventing melanoma is the highest priority for dermatologists, but I am not sure we are tackling it the right way.

In the USA, there has been a 6-fold rise in diagnoses of melanoma in the last 40 years, but no significant rise in deaths⁹. The same pattern is seen in the UK¹⁰ and in Denmark^{11 12}. The more dermatologists there are, the more biopsies are performed, the more melanomas are diagnosed- but the death rate does not significantly rise.  The introduction of checkpoint inhibitors and targeted therapies for treatment of invasive melanoma in the last decade or so, has encouragingly led to a fall in deaths from advanced disease, but this fall is nothing to do with screening. Although dermatologists advise sun avoidance, paradoxically, outdoor workers, chronically exposed to sunlight have the same or lower risk of death from melanoma as indoor workers¹³ .  Similarly, people with high measured vitamin D levels (that excellent biomarker for sunlight exposure) are less likely to be diagnosed with melanoma; have a better prognosis if melanomas are diagnosed; and are less likely to die of melanoma than those with lower vitamin D levels¹⁴.

In America there is almost no relationship between how sunny it is where you live and your risk of being diagnosed with melanoma. The strongest risk factor is living in a wealthy area¹⁵, and in the UK, melanoma diagnoses are two-fold higher in the most compared to least deprived^{16 17}. American dermatologists have a bizarre habit of doing routine ‘mole checks’ on their patients every year, which is not done elsewhere in the world as it has never been shown to reduce deaths from melanoma¹⁸. Cynics (not me of course) might say that wealth is a marker for increased surveillance and overdiagnosis.  Biologists might ask: what is happening to those early melanomas?  If we didn’t look for them and find them, presumably in most cases nothing happened.  Do they regress?  Does the immune system deal with them? Health care economists might ask: is all this effort chasing an imaginary epidemic the best use of our resources? 

When I started my dermatology training 30 years ago, there were 300 dermatologists in the UK. Now there are 1,000.  More and more of us are looking harder and harder for melanoma. 2-week-wait patients come before everything and this displaces all other dermatology activity.  And the rise in melanomas diagnosed (not deaths) goes up with our activity. We are chasing our tails and have to stop. We need a better way of identifying people who have a lesion which would spread if not removed.

At the start of each summer in ‘sun awareness week’ we are told that almost 90% of melanomas could be prevented by sun light avoidance¹⁹. The data on which this is based doesn’t stand up to scrutiny. While we have robust data for lung cancer and smoking-where incidence is closely linked to mortality - that most un-gameable of all end points- there is no such robust data for UV and melanoma.  Instead, incidence of melanoma in an early birth cohort such as people born in 1918 is compared with more recent birth cohorts²⁰.  The early birth cohort is then stated, without evidence to have had the perfect amount of UV.  Are we to imagine that people growing up in an era before widespread indoor electric lighting, televisions, computers and so on were hidden away from sunlight – maybe they spent their time indoors knitting in the dark? This cohort is then compared with more recent cohorts, who are postulated without evidence to have had much more UV exposure, but who have been seen in the era of melanoma overdiagnosis.  You feed in a 6-fold rise in melanoma diagnoses (incidence not deaths) and lo and behold - out comes the figure that almost 90% of melanomas could be prevented by avoiding sun light. It’s a lovely calculation, but as the computer coders say…’garbage in, garbage out’.

So, in summary, I think we have got sunlight wrong.  Pale skin has only evolved in the last 8,000 years in European populations, since the Neolithic transition from hunter-gatherers to farmers.  Pale skin allows us to maximise benefits from UV in a low light environment²¹. The speed at which this occurred (probably around 2% per generation) is an indicator of how important sunlight is to our well-being.  Picking apart what the benefits of sunlight are, and the mechanisms by which it acts are the focus of my work with colleagues across the University. Getting public health policy revised is the next target. 

Related links

References

1. Lindqvist PG, Epstein E, Nielsen K, et al. Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohort. J Intern Med 2016;280(4):375-87. doi: 10.1111/joim.12496

2. Lindqvist PG, Epstein E, Landin-Olsson M, et al. Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort. Journal of Internal Medicine 2014;276(1):77-86. doi: 10.1111/joim.12251

4. Cummings SR, Rosen C. VITAL Findings - A Decisive Verdict on Vitamin D Supplementation. N Engl J Med 2022;387(4):368-70. doi: 10.1056/NEJMe2205993 [published Online First: 2022/08/09]

3. Bouillon R, Manousaki D, Rosen C, et al. The health effects of vitamin D supplementation: evidence from human studies. Nature Reviews Endocrinology 2022;18(2):96-110. doi: 10.1038/s41574-021-00593-z

 5. Liu D, Fernandez BO, Hamilton A, et al. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. J Invest Dermatol 2014;134(7):1839-46. doi: 10.1038/jid.2014.27

6. Kollias A, Kyriakoulis K, Stambolliu E, et al. SEASONAL BLOOD PRESSURE VARIATION ASSESSED BY DIFFERENT MEASUREMENT METHODS: SYSTEMATIC REVIEW AND META-ANALYSIS. Journal of Hypertension 2019;37:e79. doi: 10.1097/01.hjh.0000571160.30236.81

7. Stewart S, Keates AK, Redfern A, et al. Seasonal variations in cardiovascular disease. Nature Reviews Cardiology 2017;14(11):654-64. doi: 10.1038/nrcardio.2017.76

8. Gemmell I, McLoone P, Boddy F, et al. Seasonal variation in mortality in Scotland. International Journal of Epidemiology 2000;29(2):274-79. doi: 10.1093/ije/29.2.274

9. Welch HG, Mazer BL, Adamson AS. The Rapid Rise in Cutaneous Melanoma Diagnoses. N Engl J Med 2021;384(1):72-79. doi: 10.1056/NEJMsb2019760 [published Online First: 2021/01/07]

10. Shelton J, Zotow E, Smith L, et al. 25 year trends in cancer incidence and mortality among adults aged 35-69 years in the UK, 1993-2018: retrospective secondary analysis. BMJ 2024;384:e076962. doi: 10.1136/bmj-2023-076962

11. Nielsen JB, Kristiansen IS, Thapa S. Increasing melanoma incidence with unchanged mortality: more sunshine, better treatment, increased diagnostic activity, overdiagnosis or lowered diagnostic threshold? Br J Dermatol 2024 doi: 10.1093/bjd/ljae175 [published Online First: 2024/04/24]

12. Olsen CM. Ecological evidence for melanoma overdiagnosis in Denmark. Br J Dermatol 2024 doi: 10.1093/bjd/ljae206 [published Online First: 2024/05/16]

13. Organization WH. The effect of occupational exposure to solar ultraviolet radiation on malignant skin melanoma and non-melanoma skin cancer: a systematic review and meta-analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury. 2021

14. Tsai TY, Kuo CY, Huang YC. The association between serum vitamin D level and risk and prognosis of melanoma: a systematic review and meta‐analysis. Journal of the European Academy of Dermatology and Venereology 2020;34(8):1722-29.

15. Adamson AS, Welch H, Welch HG. Association of UV Radiation Exposure, Diagnostic Scrutiny, and Melanoma Incidence in US Counties. JAMA Intern Med 2022 doi: 10.1001/jamainternmed.2022.4342 [published Online First: 2022/10/04]

16. Jiang AJ, Rambhatla PV, Eide MJ. Socioeconomic and lifestyle factors and melanoma: a systematic review. British Journal of Dermatology 2015;172(4):885-915. doi: 10.1111/bjd.13500

17. Shack L, Jordan C, Thomson CS, et al. Variation in incidence of breast, lung and cervical cancer and malignant melanoma of skin by socioeconomic group in England. BMC Cancer 2008;8(1):271. doi: 10.1186/1471-2407-8-271

18. Henrikson NB, Ivlev I, Blasi PR, et al. Skin Cancer Screening: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA 2023;329(15):1296-307. doi: 10.1001/jama.2023.3262

19. UK CR. Sun, UV and cancer: Cancer Research UK; 2024 [Available from: https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/sun-uv-and-cancer accessed 31/7/2024 2024.

20. Brown KF, Rumgay H, Dunlop C, et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. British journal of cancer 2018;118(8):1130-41.

21. Weller RB. Sunlight: Time for a Rethink? Journal of Investigative Dermatology 2024