What do girls mean when they say they need vitamin D
Maybe they need some sunshine!
It means that they need to improve their bone growth. They mostly say this when they want to bask in the sun. Lack of Vitamin D can lead to rickets which can cause muscle weakness and delayed growth.
They need sunshine
Well, vulgar girls use it in terms of needing 'dick'. i.e. "Damn it's been awhile since I got laid! I could use some vitamin D in my life!"
They need to tan