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.
The second reason for a low vitamin D is that you have primary hyperparathyroidism due to a small tumor in your neck and the body converts all the vitamin D-25 (that your doctor is measuring) to the active Vitamin D-1-25 (that doctors do not measure). This is the blue blob on the graph.
Low levels of vitamin D badly affect the bones of our body. In children, it can lead to a disease called rickets. This results in slow bodily growth and deformation of long bones like the leg bones. In adults, low vitamin D levels can cause thinning of bones and the condition is referred to as osteomalacia. It causes fragility of bones and weakens the muscles so much that one can suffer from severe muscle pain. Another disease caused due to low levels of vitamin D is osteoporosis.