The simple view of the bonding in methane You will be familiar with drawing methane using dots and crosses diagrams, but it is worth looking at its structure a bit more closely. There is a serious mis-match between this structure and the modern electronic structure of carbon, 1s 2 2s 2 2p x 1 2p y 1.
Lack of sun exposure: Lack of sun exposure is a major cause of low vitamin d level especially if you live in the northern us. Less likely would be lack of vitamin d in food, but also a possibility if you are on a very restrictive diet.
Signs you may have a vitamin D deficiency include age over 50, having darker skin, obesity, achy bones, feeling blue, head sweating, and gut trouble. Increasing levels of vitamin D3 among the general population could prevent chronic diseases that claim nearly one million lives throughout the world each year.