Re: How does your skin make vitamin D ?

Hi Joshua,
You have asked a very good question. The answer is rather complicated and 
involves a lot of complex chemical structures but I will try to give you an 
explanation in words.
I am going to start way before the skin even has a role.
First let me say that food is made up of chemicals. It does not matter what 
food you eat it is chemicals. The correct collection of the chemicals makes 
a certain food. We can analyze foods and tell you the chemicals that are in 
it and how much of each chemical is present.

When we eat, some of the chemicals in our food get converted to a compound 
called Acetyl-CoA. Acetyl-CoA is used in our bodies for many things. One of 
the things that happened to it is that it gets converted to cholesterol in 
our liver. I bet you have heard about cholesterol. People that have too much 
cholesterol have a greater chance of having heart disease than people who do 
not have too much. It is only when there is too much cholesterol that it is bad. 
Cholesterol has many uses in the body and one is to make vitamin D. 

Cholesterol can also be made in the skin in glands call sebaceous glands. 
These glands release an oily substance onto the surface of our skin. The 
cholesterol made in the sebaceous glands is immediately converted to another 
compound called 7-dehydrocholesterol. The 7-dehydrocholesterol is one of the 
things found in the oily substance our sebaceous glands secrete. When 
sunlight hits the 7-dehydrocholesterol, it gives the 7-dehydrocholesterol 
enough energy that it just rearranges itself into a chemical called 
previtamin D3. Yes, the number is supposed to be there.  All it takes is 
heat and the previtamin D3 is converted to vitamin D3. 

An interesting thing about vitamin D is that we can get too much if we take 
pills that have vitamin D in them. We say we have reached toxic levels. In other 
words taking pills with vitamin D in them could make us very sick if we took 
too many. Your skin never makes enough vitamin D to make you sick. Your body 
knows when you have enough vitamin D and stops accepting the vitamin D the 
skin made. What happens to that vitamin D if your body won't accept it? It 
stays on the skin and you wash it away when you wash. 

There is another way we remove unneeded vitamin D. Skin is constantly being 
replaced. The life of a skin cell is very short and if your body does not 
want the vitamin D the skin made it just stays in the skin cell. When the 
skin cell dies it falls off your body and the vitamin D goes with it.  

The people who look after this web site have sent me a web address that has 
information about vitamin D. You may want to read it. It may be too 
complicated but try anyway. The address is http://www.madsci.org/posts/archives/dec96/849575474.Bc.r.html
Remember that if you use any of this information for a school project or any 
other project, you should tell people you got the information from the Mad 
Scientist web site. This is called referencing your work.

Good Luck.