There is a crucial difference between D2 and D3 and in my opinion we should choose D3. Many sites state that fortified cereals and milks are a good source. I do not recommend these as they usually contain D2 which, although originally from yeast or fungus, often goes through a lot of processing and is a form that your body does not use so well. It can be calcifying in an unhelpful way especially if a person tends to be over acidic. You will see articles for and against D2 but from my research I would definately prefer the foodstate D3. It is more effective at increasing levels of 25OHD which convert to calcitriol, responsible for calcium regulation. In short we need: Sunshine ensuring your face, forearms and ideally a portion of your legs are exposed to sunlight without suncream for 15 minutes per day during summer months. This can help to build vitamin D levels. Also helpful are: the yolks of eggs, sustainably sourced and non farmed fatty fish, and whole preferably unpasteurised dairy if not vegan, a variety of mushrooms and supplementation with foodstate D3.