A portable system for determining the amount of Vitamin D generated by a user includes a computer processing unit. A database communicates with the central processing unit and stores body type information regarding a user to be monitored by the system. A geographic positioning system sensor communicates with the computer processing unit for determining a geographic location of the system. The central processing unit determines a skin darkness, and a sun intensity as a function of the output of the geographic sensor to calculate a real time Vitamin D manufactured amount for the user as a function of the body type data, skin darkness and an amount of skin exposed, and displaying an accumulated Vitamin D manufactured amount for a selected time period at a display.
