"The winter of Vitamin D"

Most people get vitamin D primarily through exposure to UVB radiation. Location and season affect the risk therefore of particular population be deficient in vitamin. During times of the year, known as "winter of vitamin D", UVB radiation in certain latitudes is too weak even to begin production of the vitamin in the skin. Ozone blocks UVB rays, and therefore its peak intensity near the equator, where sunlight path through the atmosphere is very short, and the production of vitamin D is possible all year round. Penetration angle sharper higher latitudes weakens the power of UVB rays is too low to produce vitamin, especially in winter.