Saving our Skins: Chapter 16. Balancing Acts
Saving our Skins: Chapter 16. Balancing Acts
The good and the bad of UV ...
The continuing story of “Saving our Skins”. Running with the hares and hunting with the hounds.
Updated September 5, 2021.
When we realised that ozone depletion in Antarctica could potentially lead to health risks in New Zealand, we were one of the first countries in the world to start providing UV information to the public. Reid Basher, from the New Zealand Meteorological Service coined the term “Time to Burn”, or more colloquially “Burn Time”. He calculated the burn time as the exposure time in sunlight required to elicit the first signs of sunburn. The calculation assumed the Diffey weighting function for UV damage to skin mentioned earlier in chapter 11, that had just been published. It shouldn’t really have been called a “burn” time, because it was actually only the time needed for the first detectable signs of erythema - a mild reddening of the skin which occurs 12 to 24 hours after exposure. Much less severe than what we would normally call sunburn.
At noon in summer, the burn time calculated this way can be less than 12 minutes. A very short time interval. People knew from past personal experience that they could stay outside quite a bit longer than that before they’d get a real sunburn. Had something changed? New Zealand was the only country reporting UV in this way and, because of our proximity to the ozone hole (actually, over a thousand kilometres to the south), the media interpreted this as proof that Antarctic ozone depletion was already affecting New Zealand. Good for funding, but not correct. I constantly have to remind people that New Zealand is never under the ozone hole.
At the time, I vigorously opposed the idea of burn-time, not only because it was alarmist, but also because it applied only to fair skinned people, implying that others were less important. It also didn’t take account of the way UV changed throughout the day, leading to large errors outside the noon period. But the burn time idea did have its uses. It was an easily understood concept, which invited an appropriate behavioural response: namely to restrict exposure to UV from sunlight. It also drove home the useful message that skin damage can occur in minutes, rather than hours. I now think that in principle it was more useful than what’s currently used.
At the same time, Canada had developed its own way of reporting UV risk. They reported UV in terms of a daily risk index, which ranged from 0 at night to a peak of 10 for summer at the Canada-USA border. They also used Diffey’s weighting function, which had become the de facto standard for UV reporting.
But there was still no international consensus on how UV should be reported and that was a cause of confusion. It meant that UV measurements made by different groups at different sites couldn’t be easily compared.
I was part of a small group that met at Les Diablerets, Switzerland in the early 1990s to decide how UV information should be provided to the public worldwide. We agreed that a variation of the Canadian method should be adopted. Unfortunately, that meant a departure from the usual SI units that physicists prefer (although in a sense there was already a departure because of the arbitrary normalisation of the action spectrum at wavelength 297 nm). To achieve that maximum of 10 at the Canada-USA border, we defined the UVI as the erythemally-weighted UV (in Wm-2) multiplied by a factor of 40. This definition was subsequently adopted by the World Meteorological Organisation (WMO) and the World Health Organisation (WHO). In scant recognition that the world didn’t really end at the Canada-USA border, a maximum value of “11+” was allowed. Specific colours were used to designate risk for ranges of UVI, along with behavioural advice.
But, as we later pointed out in 2014, the scale is Eurocentric. While the range is entirely appropriate for Europe, much higher UVI values occur elsewhere. For half of the world, including New Zealand, it frequently exceeds 12. And the highest UVI can exceed 25 in the tropical Andes. The colours associated with each level were also Eurocentric, with red (for danger) being used for their maximum values (UVI: 8-10), and the less threatening purple being used for UVI 11+. The associated behavioural messaging also ignored the needs of two thirds of the planet’s area, and over 80 percent of its population.
In 2018 Robyn Lucas (ANU, Australia) and I reported another flaw in reporting, which may pose a health-risk for fair skinned populations living at mid-latitudes. The flaw is that some agencies went a step further than simply reporting the internationally agreed UVI. In New Zealand and Australia some health promotion agencies defined a daily “UV Alert” period as the period of the day when the calculated UVI is greater than 3. But unfortunately, there was no consistency in this threshold. For example, USA’s Environmental Protection Agency (EPA) defined the alert threshold as UVI greater than 6. Even more unfortunately, some agencies then went on to advocate that “no protection is needed” when the UVI is less than 3. That is bad advice because at mid-latitude sites, including Lauder, the total dose of UV can far exceed the threshold for erythema on days when the peak UVI never reaches 3. And, because of cloud effects, the actual period when the UVI exceeds 3 is rarely the same as that calculated. By heeding the “no protection needed” advice, people would subject themselves to risk.
Health agencies have sought to provide one-size-fits all behavioural advice. But it just doesn’t work. UV is too variable in space and time. For the last 25 years, we’ve provided clear-sky UV forecasts for the New Zealand public. These are distributed through the media by MetService, with funding from health agencies, such as the Cancer Society and the Health Promotion Agency (HPA). But the peak daily forecasts changed only slowly and were very similar from day to day, so they weren’t interesting, and therefore lacked marketability. We also dabbled with making real-time UV Index displays for public places.
These were designed and constructed by John Robinson, one of the Lauder techs, who later became site manager. Examples can still be seen at a few schools and pools (e.g., the Alexandra Aquatic Centre). But they were too expensive to make and maintain. So, it wasn’t practicable for them to be widely distributed. A cheaper, more portable, solution was needed.
That was my motivation to enlist the help of my old friend, Jerry Burke, to develop a couple of smartphone apps (uv2Day and GlobalUV, and more recently UVNZ). I’ve known Jerry since our university days in Christchurch. He had studied physics with me, but was an early convert to computer programming, which he’d continued with until his retirement a couple of years earlier. He’s smart, had time to spare and enjoyed the new challenge. He’s also got a good sense of humour. He was visiting this morning and quoted a famous number plate from Australia’s Northern Territory. “Retired, knows everything, and has plenty of time to tell you about it” (seems rather a long number plate, but who am I to question Australian culture?). I only trust that I’m not TOO guilty of that charge here
The UV apps he developed, with a little help from me, provide the current UVI and its expected daily variability along with advice on the exposure times needed before skin damage would become visible (essentially the old burn-time in all but name). We had been alerted to the need for such detailed information by Jeremy Simcock, a melanoma surgeon whose patients needed more quantitative information on UV. Behavioural messages from the apps can be tailored to your skin type, and there is also an option of including or excluding cloud effects. The apps are freely available from the iPhone App Store or Android’s Play Store.
Of course, the real relationship between UV and skin cancer is more complicated. The UVI is defined for radiation falling on a horizontal surface. Although that may be a good approximation for beach sunbathing, it’s not very appropriate for the normal human posture. Also, there isn’t necessarily a one-to-one correspondence between sun-burning UV and skin cancer causing UV. In fact, a single photon could potentially be the trigger for DNA damage that potentially leads to skin cancer.
But there’s another side to the story too. Our initial focus on UV had been entirely on its negative aspects, as we were concerned about the effects of increased UV in response to ozone depletion. But UV has a positive side too. It’s been known for 200 years that bone diseases like rickets are associated with vitamin D deficiency, which can be remedied by exposure to sunlight. More recently, a plethora of other health issues have also been linked to low vitamin D.
We need to strike a balance between skin damage from too much UV, and vitamin D deficiency from not getting enough. Too much UV is bad, and so is too little. But what’s the right amount? The UV dose required for optimum vitamin D additionally depends on the amount of skin exposed.
We illustrated this beautifully (he said modestly) in one of my favourite plots. That was in a paper published in 2009. We first plotted the exposure times (in minutes) required to just cause skin-reddening (i.e., erythema) as a function of UVI, and we shaded in red the region of the plot above that line, denoting where there’d be more than enough UV to cause skin damage. We then plotted the exposure time needed to just maintain adequate levels of vitamin D (i.e., equivalent to a daily intake of 1000 IU), again as a function of UVI. We did this for several assumed body areas exposed (not covered by clothing) and shaded in blue the region below the line for the case where just the face and hands are exposed (as is typical in winter), denoting where there wouldn’t be enough UV for optimum vitamin D levels.
So the top right part of the plot – corresponding to high UVI and longer exposure periods - was shaded red; and the bottom left – corresponding to low UVI and shorter exposure periods – was shaded blue. The remaining unshaded area between is the “goldilocks” zone where the exposure time is just right, allowing sufficient vitamin D production without inducing sunburn. That “goldilocks” zone is rather narrow if just the hands and face are exposed. All those calculations were for a fair-skinned person (skin type II). We also showed how all these times increase for less sensitive skin types. For example, they are approximately doubled for olive skin (skin type IV) and more than tripled for dark brown or black skins (skin types V and VI). Finally, we showed how the time for sufficient vitamin D reduced as the amount of skin exposed increased, leading to a broadening of the “goldilocks” zone. The figure shown here is a simplified version of the one in our paper.
For typical summer noon UVI values (UVI=10), damage to unprotected fair skin occurs after exposures of about 16 minutes. And for the same conditions, it would take 10 minutes of exposure to your hands and face to get enough for your daily needs of vitamin D, or only 1 minute for full body exposure. But the two effects aren’t quite proportional to each other. In winter at mid-latitudes, when the UVI equals 1, just one tenth of the summer value, it takes ten times as long (~160 minutes) for skin damage, but about twenty times as long (20 minutes) of full body exposure to maintain vitamin D. Of course, in winter it’s more likely that you’ll have only hands and face exposed, meaning it would really take more than three hours. So in those circumstances, it takes longer than the time for skin damage to occur. You couldn’t get enough to maintain your vitamin D without causing skin damage.
These exposure times are only approximate because the calculations are based on the radiation reaching a horizontal surface. There are also questions about whether the blocking effect of skin colour is really the same for vitamin D production as it is for protection against skin damage. But it does give you an idea of what you need to do to get enough vitamin D without getting sunburnt for any given UVI value. All you need to know is the UVI, and the smartphone apps tell you that, and more.
The figure also showed that it’s not easy in winter to get enough UV to keep your vitamin D levels up, which is why they tend to slowly decline over the winter months (vitamin D in the blood has a lifetime of a few weeks). Gunther Seckmeyer calculated that on a mid-winter day in his hometown of Hannover, Germany, he would typically get less than 3 percent of the UV needed to maintain vitamin D at the levels recommended to maintain good bone health. Allowing for the lower UV amounts in Germany, we at Lauder could probably get no more than 10 percent of our daily requirement if our outdoor exposure patterns were similar.
Just as the threat of increased UV was starting to diminish, concerns about deficiencies in vitamin-D started to increase. We already knew that vitamin D was needed for bone health, but recent studies had shown strong correlations between vitamin D and a host of other health effects, including some forms of cancer. Our research became even more relevant to the public when we teamed up with Robert Scragg, from the University of Auckland, to find the relationship between UV exposure and vitamin D status. Our personal UV exposure is very different from the ambient UV exposures we had been measuring because people don’t just lie still in the Sun all day. We used wearable electronic UV dosimeters that had just been developed by colleagues Martin Allen at the University of Canterbury, and Zim Sherman at his spin-off company, Scienterra Instruments. The marker we used for vitamin D status was the blood serum concentration of calcidiol, also known as 25-hydroxycholecalciferol, or just 25-hydroxyvitamin D - abbreviated to 25(OH)D. Older methods to measure it had been notoriously bad, but we would use a new more accurate method that had just become available.
Study participants also received exposures to UV from lamps. This was achieved through controlled near full-body exposures in sunbeds. As part of our planning for the study, I arranged with my GP to have my vitamin D status measured before and after exposure in a sunbed. I was amazed how low it was beforehand, and how much it increased after the exposure. It later turned out that there must have been a problem with my first blood measurement because in our subsequent study, increases due to sunbed exposures were much smaller. Perhaps my first reading was low because I had a cold at the time.
We also measured the spectrum of UV coming from a few sunbeds, as in the example below where the output is compared with summer sunlight. Although the total sun-burning UV from the solarium was far greater than from our powerful 1000 W calibration lamp, it was still just comparable with that at noon on a summer day. But we also found that the UV-A irradiance from it was ten times stronger than ever occurs naturally at Lauder.
While the long-term effects of such extreme abuse are not known, it is known that exposure to radiation at UV-A wavelengths is a key factor for skin aging. Many use sunbeds for cosmetic purposes, and they would be mortified to know the longer-term cosmetic skin damage they are self-inflicting. I’ll never use one again and I strongly advise you to avoid them too.
On average, the adults in our study received less than 1 percent of the ambient UV. In winter that’s not enough to maintain optimum vitamin D levels which decline by about 20 percent over the winter months. By the end of the winter, most have sub-optimal levels of vitamin D (i.e., less than 50 nmol/litre of blood serum 25(OH)D), though most are still well above the level defined for “deficiency” (less than 20 nmol/litre).
We found that a weekly full-body exposure equivalent to less than one third that needed for sunburn causes an increase of 2 nmol/litre, which is sufficient to stop the winter decline in serum 25(OH)D. With those small weekly exposures healthy levels of vitamin D can be maintained year-round. There’s little point in having longer exposures, because further increases in vitamin D would be small, while the risk of skin damage continues to increase. We also found that the seasonal decline can be averted by a single full-body UV exposure during the winter equivalent to about half a sunburn. All this shows, that in our normal lifestyle patterns – which must be quite different from in Hannover - we’re not far away from getting enough UV, and that with minor changes to these patterns, problems of low vitamin D could be averted. There’s no need for that winter holiday in Acapulco after all, but maybe it’s not such a bad idea anyway if you can afford it.
Interest in vitamin D is starting to wane slightly because the most recent clinical trials have been less conclusive. They show that, other than for bone diseases, improvements in adverse health effects due to low vitamin D status occur only if the initial vitamin D status is very low. So, it’s probably an issue only for specific at-risk groups, who are rarely exposed to direct sunlight. This includes people with darker-skins, especially if they remain covered-up for religious or cultural reasons, and old people living in institutions.
The wavelengths of UV that produce vitamin D are not transmitted by glass, so only outdoor sun exposure is effective. Indoor exposure to sunlight through windows doesn’t help. As you age, and your skin becomes thinner, your ability to convert sunlight to vitamin D also diminishes. And without enough vitamin D the ability to absorb calcium from food needed for good bone health is diminished. That’s why many older people, especially post-menopausal women, are routinely prescribed large monthly doses of calcium and vitamin D.
There’s mounting evidence that low vitamin D is an effect of bad health, rather than a cause. A symptom, not a driver. Perhaps ill-health was the cause of my low vitamin D status mentioned earlier. There’s also speculation that it’s the UV exposure, rather than the increase in vitamin D that follows from it, that’s important. Maybe sun exposure has beneficial effects other than those mediated by vitamin D. It certainly feels nicer to soak up sunlight than it does to pop a pill of vitamin D. Perhaps the endorphins produced by sunlight have other health benefits.
Finally, our studies showed that there is a problem with current understanding of the production of vitamin D from sunlight. Common wisdom had it that no vitamin D could be produced in the winter at latitudes poleward of about 40°, but our studies contradicted that. They showed that, while it’s difficult to make enough vitamin D in winter, it should still be possible to make some. This in turn showed that our understanding of which wavelengths lead to its production must be incomplete.
But we had moved outside the area of atmospheric science. There’s ongoing debate involving the health sciences that we’re happy to be part of. It’s not central to the ozone depletion issues but shows that the issue of UV exposure and its effects on health are complex. For example, I recently learned that there are huge reservoirs of nitric oxide (that gas again) bound up in our skin. Exposure of our skin to UV radiation can release the nitric oxide into our bloodstream, which can help dilate our blood vessels, so protecting us against heart disease. It’s contentious, but if that’s true then using broad-band sunscreens may cause more harm than benefit because a lot more die from heart disease than skin cancer.
Too much UV is bad for us and so is too little. For a time NIWA management argued that we shouldn’t be doing this work as it falls outside their remit. But I think they now understand that such a silo mentality is a relic of previous times, and that our cross-disciplinary research with other communities, such as the medical sciences, is the way forward.
Next week. The most successful international environmental agreement ever …