Wow the last few weeks have been hot, and sunny, yet most of us fear the “harmful rays” of the sun that we have been told can cause skin cancer. Practising sensible sun exposure can actually help prevent skin cancer, as well as provide other health benefits and improve vitamin D levels.
UV radiation consists of UVA, UVB and UVC, UVC and some UVB rays have wavelengths between 200-289 nanometres and is completely absorbed by the ozone. UVA which is 320-400 nanometres and UVB of 290-320 are able to reach the earth and penetrate the skin, and their effects on the skin vary. UVA is able to penetrate deep into the skin effecting meloncytes (the cells responsible for pigmentation of the skin), elasticity as well as effecting the immune system. For this reason prolonged exposure to UVA is thought to be a major risk for melanoma. UVB is absorbed by DNA and reddens the skin but is less penetrating, and is responsible for the production of vitamin D. Prolonged exposure of UVB is thought to cause nonmelanoma skin cancer. A easy way to remember the difference between UVA and UVB is to think that UVA is for aging, in that it causing wrinkling and damage to deeper layers of the skin and UVB is for burning as it is responsible for bringing the reddness (blood) up to the skin’s surface and creating the precursors to vitamin D1.
The levels of UV radiation that reaches the earth is dependent on several factors including:
- The ozone – which is thinning here in New Zealand exposing us to UVC radiation
- The time of day – UV being most intense at midday
- The angle of the sun – as the sun is lower in the winter months
- Your latitude – sun’s radiation is most intense at the equator, the further North and South you go the less the UV
- Altitude – UV is more intense at higher altitudes
- The weather – dense cloud can lower the UV levels reaching the earth
- Reflective surfaces – water increases intensity as well as other reflective surfaces such as sand and snow
- Pollution – increasing pollution decreases the levels of UV reaching the earth
The recommended level of vitamin D in New Zealand is 25.0 nmol/L this is half what is now recognised by the science, therefore most of us especially if we are never out in the sun without some protection could be low in this vitamin 1. Benefits of vitamin D provided through the sun and natural body pathways include:
- Regulation of calcium and phosphorus levels, stimulating absorption. (in deficiency intestinal absoption of calcium can be reduced by half)1,4
- Plays a role in immune health, preventing autoimmune diseases 1,4
- Improves neurological health 1,4
- Decreases cancer risk 1,4
- Improves cardiovascular health, reducing hypertension and atherosclerotic heart disease, heart attack, and stroke 1,4
Ultraviolet (UV) radiation also provides other benefits to the body such as2, 3:
- An increase in endorphins leading to enhance mood and general feeling of wellbeing
- Regulation of your circadian rhythm by melatonin regulation through the “third eye” of the pineal gland photoreceptors
- Nitric Oxide induction from Ultraviolet-A (UVA) which has benefits for cardiovascular health
- In the treatment of skin diseases, such as psoriasis, vitiligo, atopic dermatitis, and scleroderma, and enhancing the skin barrier
- Reducing the pain of fibromyalgia
- Photoprotection, in the form of a tan which is thought to be protective against melanoma
- Treating neonatal jaundice
- Inducing adequate calcium absorption
So how long is too long? Guide to sun exposure for optimal vitamin D
As you have seen there are a lot of variables which effect how long we can stay in the sun in terms of the level of UVB and UVA rays without any protection. Another risk factor is the type of skin you have1 :
- TYPE 1 – I always burn, never tan and am fair with red or blond hair and freckles (albinos, some redheads and some Scandinavians and Celts)
- TYPE 2- I easily burn, hardly get a tan, am fair skinned (people of Northern European origin, Germans and some Scandinavians and Celts)
- TYPE 3 – I occasionally burn and gradually tan (people of Mediterranean and Middle East origin)
- TYPE 4 – I rarely burn and always tan (people of East Asian origin and some Indians and Pakistanis)
- TYPE 5 – I seldom burn, always tan and have medium to dark skin (people of African origin, South East Asians and some Indians and Pakistanis)
- TYPE 6 – I never burn and tan darkly (people with “blueblack” skin, people of African origin and dark-skinned Asians such as Tamils)
People with type 1 skin have the highest risk of skin cancer and those with type 6 have the lowest. The reason for those with type 1 skin being high risk is that they do not produce the body’s natural protective melanin pigment (which is responsible for a tan), and therefore have no natural defence against skin damage. The opposite is true for those with type 6 skin. Knowing your skin type is important as this will also affect how long you can stay in the sun. It is important however to protect your eyes and face regardless of type, by wearing a hat and using sunglasses.
Holick Solution to getting sensible amounts of sun exposure:
- Estimate how long it takes in the particular conditions in which you will be sunning yourself for you to get a mild pinkness (known as one minimal erythemal dose or 1 MED)
- Then without applying sunscreen expose your arms and legs for about 25-50% of that length of time. That amount of exposure 2-3 times a week enables the body to create enough Vit D to stay healthy
- After this amount of sun exposure, protect your skin by covering up or using a broad-spectrum sunscreen (i.e. one that filters both UVB & UVA rays) of at least SPF15 and preferably SPF30 and follow instructions to reapply when necessary.
A word about sunscreen
Apart from the toxic and endocrine disrupting chemicals that can be found in most sunscreens, sunscreen has also been thought to contribute to the formation of melanoma specifically and the reasoning behind this is that we were concerned mosting with burning and therefore initially sunscreen blocked the UVB rays (which also blocks vitamin D formation) but not the UVA rays which as you now are aware, penetrate deep into the skin and damage the melanocytes. This allowed us to stay out longer and be exposed to the dangerous levels of UVA radiation. If you are going to need to use a sunscreen, i.e. if you are planning on being out in the sun for an extended period of time make sure your sunscreen protects you from all UV radiation. Consumer compared a few of our New Zealand sunscreens and the results can be seen here.
Video from Vitamin D researcher Michael Holick, explaining how the body reacts to sunlight and a history of our understanding of how the sun affects health.
1. Holick, M. (2010) The vitamin D solution. A 3-step strategy to cure our most common health problems. Plume, Penguin Group
2. Juzeniene, A. & Moan, J. (2012) Beneficial effects of UV radiation other than via vitamin D production. Dermato-Endocrinology, 4(2), 109-117. doi: 10.4161/derm.20013
3. Wurtman, R. (1975).The Effects of Light on the Human Body. Scientific American, 233(1).
4. Grant, W. B., Wimalawansa, S. J., Holick, M. F., Cannell, J. J., Pludowski, P., Lappe, J. M., … May, P. (2015). Emphasizing the health benefits of Vitamin D for those with neurodevelopmental disorders and intellectual disabilities. Nutrients, 7(3), 1538–1564. http://doi.org/10.3390/nu7031538