Give me 5 reason why does people need sun?

Have you tried the following search? If you click on it and then the subsequent links on it, you will find some helpful information.

Benefits of Sun Exposure - Google Search

Vitamin D
Don't have seasonal affective disorder
The sun energizes me.
People assume tanning bed is safer when it isn't
How many beach bums have actually died of cancer from the sun
And do others in colder climates really get as much sun as the sun worshippers at the beach do?

On the bright side, sun exposure had benefits

WomenOf.com: It's Not All Bad: The Benefits of Sun Exposure.