I had a friend ask if they could get vitamin D through a window. I figured not, but of course had to look it up.
We need vitamin D to help the body absorb calcium and phosphate from our diet. These minerals are important for healthy bones, teeth and muscles. The body also needs vitamin D to keep the nerves, muscles, and immune system working properly. A lack of vitamin D, known as vitamin D deficiency, can cause bones to become soft and weak, which can lead to bone deformities.
In children, for example, a lack of vitamin D can lead to rickets. In adults, it can lead to osteomalacia, which causes bone pain and tenderness or a porous, fragile bone condition called osteoporosis.
Our body creates vitamin D from DIRECT sunlight on our skin. Your body can't make vitamin D if you're sitting indoors by a sunny window because ultraviolet B (UVB) rays (the ones your body needs to make vitamin D) can't get through the glass. We also get some vitamin D from a small number of foods, including oily fish such as salmon, mackerel, herring and sardines, as well as red meat and eggs.
Vitamin D is also added to all infant formula milk, as well as some breakfast cereals, fat spreads and non-dairy milk alternatives. The amounts added to these products can vary and may only be added in small amounts. Manufacturers must add vitamin D to infant formula milk by law.
Another source of vitamin D is dietary supplements.
Most people can make enough vitamin D from being out in the sun daily for short periods with their forearms, hands or lower legs uncovered and without sunscreen. It's not known exactly how much time is needed in the sun to make enough vitamin D to meet the body's requirements. This is because there are a number of factors that can affect how vitamin D is made, such as time of day, geographical location, skin color, wearing sunscreen, and how much skin you have exposed.