Vitamin D is important for muscle and bone health. Vitamin D deficiency
is associated with cortical bone loss, increased bone turnover, and increased
parathyroid hormone levels, predisposing to osteoporosis. Vitamin D
supplementation increases bone density in established deficiency. Historically,
the main source of vitamin D was exposure to sunlight. However, changes in
lifestyle and awareness of the hazards associated with sun exposure have changed
this. Also, Sunscreen sun protection factor 15 (adequately applied) reduces previtamin
D synthesis by >99%. At latitudes greater than 35 degrees (MN is at 40
and greater degrees), UVB energy is insufficient to produce vitamin D during the
winter months,4 producing a ‘vitamin D winter’ of variable duration, centered on
the winter solstice. During these times of no cutaneous vitamin D production,
dietary intake of vitamin D and previous vitamin stores become important.
Treating deficiency involves correcting the vitamin D deficit and ensuring
continuing maintenance of vitamin D status.