Eli5: Do you need (some) sunlight to be healthy, or could a special diet replace what you get from it?
In: Biology
In order to build vitamin(s) D you need exposure to UVB light. One of the preliminary molecules passes through your skin, where UVB light changes its chemical structure. UVB light is *ionizing radiation*, meaning it has enough energy to knock electrons off of their atomic nuclei, ionizing the atom. Normally, that’s bad because if the atom happens to be in a molecule of DNA, it will damage the DNA and can lead to cancer. However, it’s also a useful tool like for synthesizing vitamin D.
Vitamin D is important for helping you absorb calcium, magnesium, and phosphate from the food you eat as it passes through your intestines. Without enough vitamin D, you will, among other things, develop weak bones. In children, this leads to the disease *rickets* where the bones are soft and bow outward as the child learns to walk and put weight on them.
Fortunately, yes, you can just take a vitamin D supplement. There aren’t many foods that naturally include vitamin D, but it’s easy enough to add to foods. Milk – especially cartons made for children, like those found in schools – is often fortified with vitamin D because, hey, you’re drinking the milk to help with calcium so it makes sense to include the molecule that tells your body to absorb that calcium better.
Exposure to sunlight (specifically UVB light) causes your body to produce Vitamin D. If you do not have exposure to sunlight, or you do not get Vitamin D from some other source, you can get sick.
Luckily there is nothing magical about sunlight and you can get the same effect from other sources. For instance, you could use artificial UVB light to stimulate your body to produce Vitamin D. You can also get Vitamin D from eating certain foods which contain it naturally, or take a vitamin supplement.
Many people living modern lifestyles do not spend enough time outside to get Vitamin D naturally. People also tend to eat junk food which does not contain enough Vitamin D. Because its fairly cheap, some companies now advertise vitamin enriched food as an alternative to a healthy lifestyle.
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