i read something interesting recently about vitamin D 
factoids:  it sticks to me like Glue...so i'll pass it along to ya's...
your Skin acts like a big receiver converting direct sunlight
into vitamin D  and you need about 10 to 15 minutes exposure
to get some benefit...  That i knew !
what i recently learned was that our EYES having the most receptor cells of all
 concentrated in a compact area --> does this incredibly well too....
but 
not Obviously if your always wearing Sunglasses
so , do the same thing -let in some sun for 10 minutes per day
as long as your not driving ....