Vitamin D is really a hormone, not a Vitamin and it is needed for many processes that regulate the body's health. Mammals use it to build bones and its importance was discovered when around a hundred years ago doctors saw that rickets could be cured by adding Vitamin D. Now, it is believed that it affects much more than bone health, from diabetes to cancer, even including mental health.
The main way, and the healthiest, to obtain your Vitamin D is from the sun. The problem lately is that, because of skin cancer and dermatologist recommendations, we are afraid to be out in the sun completely, or when we are, we cover ourselves in sunscreen, which blocks Vitamin D absorption. Fortunately, you do not need that much sun exposure to get the Vitamin D. Just 15 to 30 minutes of sun in your arms and legs from 10am to 3pm two or three times per week should be enough if you live south of Atlanta. North of Atlanta, you definitely should get sun in the Summer and you may need to take a supplement as well. Food is not a great source of Vitamin D. Only oily fish, like wild salmon (be careful with farmed varieties), would have some, and even so, you would have to eat quite a lot to get adequate amounts. Fortified milks are another source (although, as I don't eat dairy, not for me). Here you can find more specific recommendations according to where you live from Dr. Greger. Or here, there's an interesting article from WebMD about the topic.
To see if you need supplementation (and, actually most of us do) you should get a blood test, the 25-hydroxy Vitamin D or 25(OH)D test. The official recommendation as to how much Vitamin D you need has been changed lately, from 20 ng/mL or above to between 30 and 40 ng/mL. My nutritionist actually wants me to have at least 80 ng/mL. Can you get too much Vitamin D? Yes, so you should be a bit careful, although, from what I have read, it is quite difficult to get to toxic levels (more than 150 ng/mL) and you can never get to those levels just with exposure from the sun. Another reason why sun exposure is always the best way to get your Vitamin D. For my family in Spain reading this, I doubt you would need any supplementation. Just make sure you walk outside everyday (also good because of the exercise).
I hope I don't transmit fear mongering here. I just think there are way too many advantages (which I had no idea before) to having an adequate amount of Vitamin D, one of them being the prevention of cancer, and it is relatively easy to do. Just don't be afraid of the sun. Make sure that after your 30 minutes you do put sunscreen on and also know your level of 25(OH)D so you find out whether you need to take a supplement or not.
Here's some more information I hope you find interesting:
- NYT: Reasons that Vitamin D May Matter
- Here you have, not one, not two, but twelve! videos from Dr. Greger about Vitamin D.
- WebMD: Slideshow, the truth about Vitamin D
- ABC News: In Tests, Vitamin D shrinks Breast Cancer Cells.
A lot of information today. Let me know if everything is clear and if you have any more information about Vitamin D that we should know about!