This may seem like a dumb question. Do sunglasses have an effect on vitamin d production? Does vitamin D production rely strictly on exposure to sun, or do you have to see the sunlight? Blind people obviously produce vitamin D, but in what quantities?
This following extract is from an article about light deficiency and the effect of artificial light on the body, it has some interesting information about light entering the eyes:
HOW SUNLIGHT ENTERS YOUR BODY Ninety-eight per cent of sunlight enters through the eyes, and 2% through the skin. The 2% on the skin is important because that is the only way your body can develop vitamin D which is essential for calcium production to make strong bones and strong teeth.
LIGHT TRAVELS IN THE BODY Light enters through your eyes and follows two pathways, each of which has a different effect: (i) The visual pathway, which enables you to see, is the upper pathway, which goes up to the cortex. If you're blind, that pathway may be blocked, but the lower pathway continues to function. (ii) The lower pathway goes to the hypothalamus gland, an extremely important gland in the distribution of sunlight to the rest of your body.
SUNLIGHT AND ENERGY The hypothalamus has another important duty and that is converting light to chemical electrical pulses that follow the nervous system in the body, providing energy to every cell in your body. Your cells require nutrients from foods, and oxygen from the air, but what ignites energy in the cell is light. Sunlight is the spark plug, which provides the spark in cells to produce protein, and to replicate and repair. This is the mechanism of sunlight in the body. It regulates the body clock; it produces the hormones in your body and it produces the energy that goes to the cells, so it's important that good light enters your eyes.
It talks about the effect of sunlight (or the lack of it) and wearing sunglasses:
SUNGLASSES There are three reasons to wear sunglasses: glare, glare, and glare. Other than that, I would prefer you not to wear sunglasses, but if you have to I would recommend charcoal grey. Any charcoal grey, non-polarized lens is the best blocker of glare imaginable. And also, since it's charcoal grey, there will be no distortion of colours. They are literally full spectrum. And if you are lucky enough to find some manufacturers that produce lenses that allow some ultraviolet to come through, you benefit from that too, especially during the wintertime.
So to answer your question, wearing sunglasses will not effect vitamin D production, as it is made through the skin, however, you need to allow sunlight into your eyes for other important processes in our bodies which involve the hypothalamus gland. Blind people are not affected by not having the 'seeing' pathway, as the 'hormone pathway' continues to function.
As an aside: it is worth reading this article just for the information on artificial light and the effects it has on health - it is an eye-opener ;)
That's a very interesting question, actually. I don't think many people have thought of it from that perspective.
While it has been established that vitamin D production occurs in the skin, that is not to say that there may not be other mechanisms elsewhere that regulate the level of production. It could well be that, like you say, there is a neurological/psychological component, whereby the body gauges the sun exposure not just by how much UV reaches the skin, but also by how much it can see (brightness, duration). A bit like the way the mere sight of food can stimulate gastric acid production or insulin secretion even before any food has entered the mouth (learned reflex? adaptive behaviour?) Also, a lot of biological processes are influenced by information that reaches the eyes, starting with circadian rhythms.
Perhaps visual exposure to sunlight is used by the body to sense changing seasons and thereby incluences its internal circadian rhythm, which might in turn have some bearing on vitamin D production (upregulating or downregulating key enzymes, for instance).
Just pure speculation here...
It would be really interesting to carry out a study in the direction you suggest, by comparing the D3 production in blind people with sighted people and also sunglass wearers. Though I very much doubt it is on any researcher's top priority list, unfortunately.
I would say- NOPE, it is not produced through the eyes. Vit D is produced when sunlight (UVB of a certain wave length which we are now in that time of the year -blossoms to leaves turn color is the time frame) reacts on the skin's cholesterol precursor called 7-Degydrocholestrol- so get outside in store as much as you can- expose some skin. Women, I cannot over emphasis the importance of skin expose. For men that is taken thru the yes.
I can't remember where I read this, but it works for both my husband and me.
NOT wearing sunglasses makes us both less likely to get a sunburn. I don't know that it has anything to do with D production, but we both supplement that.
I also lay out in the sun every day I can (in a bikini or less).
Vit D is not produce through the eyes. A blind person is at no disadvantage becuase his eyes don't work properly for vision. Vit D is produced through the skin and depends on the length of the UV wavelengths according to where you live on the Earth. Must of us live in the Temperate region and as a rule spring blossoms to Autumn foliage is the time when the wavelengths produce Vut D when in contact with the skin. Like wise, Year round at the tropics and NEVER (although extremely bright) inside the Arctic circle.
There are extreme mood swings from sunlight that pass through the eyes that comes from the color spectrum that effect folks in the long winters, especial near the arctic but this has zip to do with Vit d production. Wear your sunglasses but take off that shirt for about 20 mins a day for best production.
well, I think it is. I read a comment today (http://www.naturalnews.com/031682_rickets_sunscreen.html)that was made an experment, and blind people dont get Vitamin D, because it is produced only trough eyes. Even when they were exposed to a sun bed they didnt produced vitamin D.
Actually, that rickets article just confirms that UV light is NOT absorbed through the eyes in amounts sufficient for VitD production. Mom slathers sunscreen on child, blocking UV absorption of the SKIN. Child, whose eyes have not been sewn shut or creatively removed, is then allowed to play in the sunlight as much as she wants so long as her skin is slathered in UV-blocking sunscreen. Said child of the fully functional eyes then develops rickets from Vit D deficiency. The only thing limited in this system is the ability to absorb UV through the skin, not the eyes.