11 February 2008

Sunglasses can cause sunburns?

This weekend I was without a book to read, so I decided to give Survival of the Sickest, by Dr. Sharon Moalem and Jonathan Prince, a try (my boyfriend's parents had mailed him this book and it has been collecting dust every since).

In chapter 3, he talks about the roles of cholesterol and melanin (the pigment responsible for our skin and hair color) and the trade-offs between getting enough vitamin D and folic acid (folate). Vitamin D is made in the skin by using UV B light and cholesterol, but UV light also breaks down folic acid which is needed for cell growth, DNA replication, and red blood cell production.

Anyway, in the chapter he goes on to elaborate that exposure to the sun makes us tan because this stimulates our pituitary glands (which gets its information from the optic nerve) to produce a hormone that triggers the melanocytes in our skin to make more melanin. So when you wear sunglasses, less sunlight reaches your optic nerve, and less warning is sent to your pituitary gland, and less melanin is made. Since melanin is there to protect our cells from the damaging effects of UV radiation, we will be more likely to get a sunburn. In short, wearing sunglasses can cause sunburns.

This story has to be far more complex than he lets on however. Why can't I get tan by say sticking my head out my window and staring at the sun for a while? Why do people get tan in tanning beds if their eyes are covered by those little plastic goggles? Some searches on the internet didn't provide me any answers to these questions - perhaps I need to look in some medical books. Feel free to comment if you can share some wisdom on this topic.

For now, I'll keep wearing my sunglasses and using sunscreen. As for vitamin D, daily vitamins will do the trick.


Eva said...

Hm, well my PhD project is on pigmentation, so I should probably know, but I've never read anything about the sunglasses idea. Then again, I'm only looking at single cells (and mainly reading about cellular models and about mice - who don't wear sunglasses and who don't tan! Humans and guinea pigs tan, but mice don't.)
As far as I know UV light has a direct effect on skin pigmentation in humans through early DNA damage: melanin synthesis is triggered by a range of different stimuli, and one of them is the detection of small fragments of DNA as a result of UV damage. So by the time you tan, your DNA is already damaged and the tanning is a natural defense mechanism.

Amy said...

Thanks for your comments Eva! DNA fragments make sense as a stimuli for melanin synthesis.

Guinea pigs can tan? I think we should strap on some sunglasses and see if that has any effect. :D

workboy53 said...

A total of 5,171 people were observed simultaneously by two independent observers, and the inter-rater reliability use of sunglasses was excellent (Cohen's kappa = 0.83). Overall, 33.0% of people wore sunglasses when observed.

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Vince M said...

we also have photoreceptive cells in our skin..there must be enough of them to trigger the response. they are in concentration in the center of the brain (pineal gland) in our eyes, around the eyes and scattered all over the skin. hope this helps to answer your question.

Vince M said...

it is hard to find the research paper on photo repair. but in a nut shell it proves that the cell can be damaged 95% by UV it also showed that the cell can be healed back to 100% with uv.also check out the photom DNA experiment. i use to use sun screens and sun glasses.. i use to bleed when i used sun screens. extreme DNA damage, now i just tan.. research how many diseases were cured with heliotherapy in the 20's..

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Marian Smith said...

Maybe, when buying a sunglass you should choose that has UV protection. There are many sunglasses for sale that have this characteristic.