asalaamo alaykum the sunlight does not give vitamin D it activates it. It cannot be activated through a window or inside a car but with direct contact. You should get vitamin A and D together. from what i know vitamin D deffency is from lack of being outside not wearing clothes. People spend too much time in air condition homes, dont excersise and eat malnourished processed foods. For vitamen D take supplements. Dont take cheesy store bought supllements too. they are watered down cheap valued herbs. a good source for good herbs are Amazon herbs, cedar bear naturales, gaia herbs, Grandma's herbs, Limited edition, red rock naturals, LIfe extension, and the best is natures sunshine. We lack nutrition all around not just vitamin D. people are dying and getting cancers and other chronic illnesses because of the health care systems and food industies. wasalaam take care Chris