Vitamin D is a happiness hormone which is also essential for health in many ways.
Vitamin D activates the immune system: "with vitamin D in the bloodstream, T cells become "armed" and begin seeking out invaders that are then destroyed and carried out of the body"
There is a 'vitamin D' winter if we live a long way from the equator; the length of this winter depends on the exact latitude - you can get a more exact idea in the article that follows. In Britain it is from approximately September to March. The latitude determines the angle at which the sun's rays reach us and therefore the amount of UVB radiation we receive. It is UVB rays that create vitamin D3 in the skin.
"Sunlight has long been recognized as a major provider of vitamin D for humans; radiation in the UVB (290-315 nm) portion of the solar spectrum photolyzes 7-dehydrocholesterol in the skin to previtamin D3, which, in turn, is converted by a thermal process to vitamin D3. Latitude and season affect both the quantity and quality of solar radiation reaching the earth's surface, especially in the UVB region of the spectrum, but little is known about how these influence the ability of sunlight to synthesize vitamin D3 in skin. A model has been developed to evaluate the effect of seasonal and latitudinal changes on the potential of sunlight to initiate cutaneous production of vitamin D3. Human skin or [3 alpha-3H]7-dehydrocholesterol exposed to sunlight on cloudless days in Boston (42.2 degrees N) from November through February produced no previtamin D3. In Edmonton (52 degrees N) this ineffective winter period extended from October through March. Further south (34 degrees N and 18 degrees N), sunlight effectively photoconverted 7-dehydrocholesterol to previtamin D3 in the middle of winter. These results quantify the dramatic influence of changes in solar UVB radiation on cutaneous vitamin D3 synthesis and indicate the latitudinal increase in the length of the "vitamin D winter" during which dietary supplementation of the vitamin may be advisable."
Vitamin D is fat soluble, and needs to be taken with fat in order to be properly absorbed ...there are two common types of vitamin D: Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol). We need vitamin D3 rather than vitamin D2. You can obtain softgel D3 supplements. The richest food sources include fermented fish liver oil, butter (preferably raw) and high vitamin butter oil.
"Even indoor tanning beds may have their proper use...After exposure to UVB rays, make sure you wait as many hours as you can before showering. Why? After UV exposure, your skin produces a powdery substance that is then absorbed into the skin and converted to vitamin D by the body. If you wash this off too early, you interfere with the amount of vitamin D made....