ABSTRACT
When the earth was born and bathed in sunlight, life forms quickly took
advantage of the sun’s energy by converting it into sugar, which not only
sustained life but also helped it to thrive. It is likely that a wide variety of
photochemical processes occurred throughout early evolution. One photosyn-
thetic process that has been occurring in phytoplankton for more than 750
million years is the photosynthesis of vitamin D. Although the exact function
of vitamin D is unknown in these simple life forms, it has been suggested that
the formation of vitamin D in the plasma membrane of these single-celled
plants was important for calcium-ion transport into the cell. Also, vitamin D
and its photoproducts absorb ultraviolet radiation that is identical to DNA,
RNA, and proteins and thus could also have served as a natural sunscreen (1,2).
