Unlike other vitamins, vitamin D is created naturally by the body when the skin absorbs ultraviolet sunlight. But with sleet, snow, freezing temperatures and gusting winds during the winter, people bundle up and spend less time outside in the sunlight. Plus, during this time direct sunlight is hard to come by due to the Earth’s tilt away from the Sun.
"Every cell in the body is responsive to vitamin D," Horvath said in a statement. "If you’re deficient, you won’t see the health effects for years and it could take months to get your levels back up." Vitamin D deficiency could cause lower bone density, a weakened immune system, increased risk for type 2 diabetes, cancer and cardiovascular disease, and cognitive impairment in older adults.
Those who are most at risk of vitamin D deficiency are the elderly, pregnant and nursing women, and people of color, whose skin acts as a natural sunscreen. Pregnant women and nursing mothers are of particular concern because it affects children at a time when their bones are still developing. This could result in rickets, or the softening of bone.