We get vitamin d from the sun. sunscreen lessens our ability to absorb it. A lot of people are now deficient. The best way to get the levels up are with a prescription supplement. I took 5000iu daily, for a year and levels were lower. The Dr prescribed 50,000iu once weekly. My levels are up but not yet where they need to be. I don't think you can get enough if you are deficient with anything but a very high dose. I have found what they sell off the shelf just doesn't work. Also it is best to take d3.