vitamin D deficiency explained?

i heard a novel idea about why so many people are suffering from a vitamin D deficiency--even though so many foods are fortified with it.

we are too clean.

cholesterol on our skin is what interacts with sunlight to help the body manufacture vitamin D.

it takes 24-36 hours for cholesterol to reach the skin.

bathing removes it.

so--the point is, i guess, when you're dirty, let the sun shine on your skin!!!