Sunlight is good for you. Or why it is not all bad.
By Gavin Greenoak, Managing and Scientific Director of the Australian Photobiology Testing Facility, at the University of Sydney.
If the sun did not exist, nor would we. Our planet goes around it, according to an attractive force. According to some it is a fiery thermonuclear power source. To others it is an electrical dipole of plasma energy. It emits light, an electromagnetic spectrum of wavelengths, and/or particle velocities. And then, as Plato said, “How should we see, unless our eyes are first sunlike.” We have evolved, even from the slime mould, with this light, this warmth, this day and night, this seasonal gradation. And when I take off my white coat and walk out from any official view, the sun, is a wonder, in all these respects, and is a perennial symbol, of a thing that gives of itself, and holds amid the sublime phenomena of our days, and remembered by the stars at night, the glory of most glorious light. Every day.
And there’s another thing, that we might remember, that while we have abundant and coherent theories about sunlight, and many of them confirmed in fact, whatever we may think the sun is, this knowing will always reflect our relation to it. Somehow our knowledge never contains the sum of our experience of it. The sun is the assumption of all life as we know it. And it shines upon the just and the unjust, alike. Or perhaps it doesn’t. Perhaps, only if our understanding of the sun, is just, and not merely scientific, whereupon we must admit all our knowledge qualified, by our limited human status. Not yet God. And so we may wonder, and let that wonder qualify our appropriations, appropriately. The sun would seem a part of us, and we are a part of it. And truth must admit poetry, as well as science, into the reality delivered by our experience and understandings.
So the sun is good, and only bad when we get too much of it. And our awareness of the sequelae of over exposure can teach us something of that respect we already show to the oceans which break so hugely on our shores, yet also invite our enjoyment.
The sun in some climes is a gentle giant, and in others it is ferocious, blasting, and terrible. Yet deserts too have their own, secretive lives. But to get caught in the Australian desert, without shade, and without a sunscreen, could well be fatal.
The indigenous people of Australia, have a skin type naturally adapted over thousands of years, to the Australian sun. Darkly pigmented, the granules of melanin, provide umbrella like shade and protection to the nuclei of cells in which these granules are distributed in the upper layers of the skin.
Migrants to this country, from anywhere where the sun is less intense, are not going to have this adaptive skin protection. And we are going to be vulnerable therefore, to receiving, and suffering, much more sunlight than we need. So we do need to reduce the amount of sunlight, in particular ultraviolet light (UVL) that reaches our skin. And we can do this, in a wide variety ways, including staying out of it in the middle of the day, finding shade, wearing clothing, hats, eyewear, and sunscreens. And remembering that all of the results of over exposure to sunlight are delayed responses. Even sunburn, creeps up, until it’s too late to avoid it. Skin cancers can be delayed from childhood to past the middle of life. And premature skin ageing comes some way after a tan all too vigorously pursued and maintained. Skin cancer is no fun, and while we may often intervene before the danger turns malignant, melanoma is the most malignant of cancers, and the incidence of it continues to rise. Australia remains, the skin capital of the world.
On a summer’s day in Sydney, five to ten minutes of sunlight twice a week, on unprotected face and hands is considered enough to provide sufficient Vitamin D. From dawn until around ten in the morning, and as the angle of the sun drops below forty five degrees in the western sky, we can be a little more relaxed, but we will soon feel the sun bite when the sun is high. If you go swimming, remember to reapply sunscreen as quickly as you can.
Vitamin D is important, and as well as playing a role in the formation and maintenance of bone, it appears to have its own anti-cancer effects. Too little sunlight can lead to a deficiency in this vitamin.
Figure 1 shows a paradigm of health as a function of dose, whether it be sunlight, water, or air. We don’t want too much, and we don’t want too little. All are necessary to our health.
At the University of Sydney we have also been looking at dietary influences on the susceptibility of the skin to both sunburn and non-melanoma skin cancer. We had an hypothesis that for an important suite of mainly adrenal hormones to be activated as a part of the adrenal, hypothalamus, pituitary axis, hunger is a trigger. And our laboratory animals, like many people, do not get hungry. They graze. So all we did first was to limit access to food to six hours a day. In this time the animals ate as much as those eating all day, and occupied there non-feeding times with a greater activity. When we exposed this group of animals, together with a grazing group, to the same repeated doses of (non-burning) sunlight the number of skin cancers appearing was reduced by over ninety percent. And sunburn was delayed.
So we can optimise the health and resistance of our skin to damage, by eating our main meal in the middle of the day if possible, avoiding grazing, and not having big meals at night when the body wants to go into repair, rest, and recovery mode, and does not want to detour resources to digestion.
Sunlight is essential to healthy life, but we do not want too much of it. To be aware of sun exposure reduction strategies in Australia is essential for its fullest enjoyment. We used to say, “exposure minimisation”, but the most minimal is none, and we do need some.
The thing to aim for is of course “balance”, and we hear this aspirational word in many contexts these days. And of course when it comes to balancing, no one can really do it for you. You might look to experts to give you authoritative advice, but given the diversity, the generalisations are fraught.
Thus it may be, that a timely benefit may come to pass. Our bodies are in themselves extraordinarily sensitive measuring instruments. But our attention to this, and our ability to read its signs, has not been granted much value.
On the surface of our skin is a substance called urocanic acid, which absorbs ultraviolet light and undergoes photochemically driven change. Some excellent work from the MD Anderson Cancer Center in Houston Texas has shown clearly that this surface substance mediates a “high” via receptors and pathways shared with psychotropic drugs. We do not need much sunlight for this “isomerization” to occur, and many people feel this pleasurable effect. We are then led to ask, from an evolutionary point of view, and given the ubiquity in mammals of this skin surface substance, why if sunlight is bad for us it might have occurred in the first place, and is highly conserved. The question of course is rhetorical, because sunlight is not bad for us, but the existence of urocanic acid, and the “high” it induces, does rather more than underscore the benefits it confers. However, this high, will also “come down”, as highs do, and we will experience a distinct discomfort. And this may very quickly overwhelm the pleasure it followed.
As a Celt myself with pale-ish skin, for example, I like to swim at dawn, and I know that until the sun is up in the sky more than forty five degrees, I am not going to be getting much of the UVB which will most effectively burn my skin. Up just a bit higher, and something happens which I call “the bite”. It is distinctly uncomfortable, and the ready sign that my morning at the beach is over.
While the notion of “balance” is a real challenge for health educators to communicate, I think it represents a very healthy turn of attention to the value of this extraordinary thing the body is, - your body, and its wealth of sensitivities, we may slowly come to better understand, and trust.