http://www.energyfirst.com/Vitamin-D : A deficiency in D should not be taken lightly.  In children it can cause a disease called rickets, in which their bones become weak and are subject to bowing under pressure.  In adults being deficient can cause soft bones or ‘osteomalacia’ which can lead to breakages in the spine, hips, and other bones and can also contribute to osteoporosis.  Seniors should consider being on a vitamin D regiment to help prevent this disease.