Is the sun really a good source of vitamin D? How does this work?

It is indeed! There are two main source of Vitmain D; our foods, and UV light. Unlike any other vitamin, our main source of Vitamin D is not through our food, but rather from our exposure to UV light. The following sequence is how Vitamin D is formed with the use of UV light:

1. The skin produces a the molecule 7-dehydrocholesterol which absorbs UV light from the sun, resulting in pre-vitamin D3.
2. Pre-vitamin D3 spotaneously becomes Vitamin D3 through a process which takes just under 2 weeks!
3. Vitamin D3, also known as cholecalciferol, is transported around the body in the blood to the liver where it is hydroxylated. This means a hydrogen atom is added, resulting in 25-hydroxycholecalciferol
4. 25-hydroxycholecalciferol, also known as calcidiol, is transported to the kidneys where it is again hydroxylated to become 1,25-hydroxycholecalciferol. This process is using the important enzyme 1-alpha-hydroxylase.
5. 1,25-hydroxycholecalciferol, is also known as Vitamin D!!

So you can see, the process of producing the bioactive form of Vitamin D is a multistep one involving the skin, liver and kidney. Just so you know, the vitamin D we ingest from food comes into the flow chart at step 3 as cholecalciferol.

Vitamin D helps the body absorb calcium through the small intestine. As you will know we need calcium to maintain healthy bones, muscles and teeth. The perception that the sun is a really good source of vitamin D, is related to the fact that ultraviolet radiation from the sun is the best natural source of vitamin D.

Most people get enough vitamin D through exposure to sunlight during normal day-to-day outdoor activities. However, some people have very low levels of daily sun exposure. This can lead to low vitamin D and, in some cases, longer term deficiency.

Having said that, I can tell you that both my mum and dad have Vitamin D deficiency. What is strange is that mum hardly goes into the sun, but my dad walks 2 hours a day...so am not sure exactly why he has any deficiency.

comments

Vahid Ta'eed: The need for Vitamin D increases with age. Latitude and pigmentation could be part of the problem.
1 year ago

Corinne Mirkazemi: I believe either 25 hydroxy-vitamin D or 1,25 dihydroxy-vitamin D levels are measured when a person is tested for deficiency. Looking at Anis' detailed explanation of the process of how vitamin D becomes activated, you can see that both 25 hydroxy-vitamin D or 1,25 dihydroxy-vitamin D are at the end of the process - i.e. the activated forms that require the liver and/or kidney to activate them. Fuad, if your father's liver or kidneys or both are not functioning properly, this can also result in low vitamin D levels when tested.
1 year ago

Technically the sun is not a source of vitamin D. Sunlight is purely electromagnetic radiation. However, as @Anis said above, the UV component of sunlight is a critical component in the body's production of vitamin D.