Vitamin D is a fat-soluble vitamin which promotes the healthy functioning of the body in many ways. It facilitates the absorption of calcium and phosphorus in our body and helps in strengthening the bones. It also plays a great role in strengthening our defense against the harmful bacteria, viruses, and other pathogens. Out of the five forms of this vitamin, ergocalciferol and cholecalciferol are believed to provide great health benefits. The human body naturally synthesizes it when it's exposed to sun. This vitamin is biologically inert in nature, and becomes active only after it undergoes certain reactions. One can consume foods that are rich in this vitamin or naturally get it by basking in the sun. Certain studies have also shown that this vitamin has a positive effect on the nervous system. This is why studies are being conducted to establish a link between a vitamin D deficiency and mood disorders. Vitamin D Deficiency and Depression It is believed that there may be a connection between a depression and a deficiency of the sunshine vitamin. No wonder, the use of vitamin D supplements is suggested for alleviating the symptoms of seasonal affective disorder (SAD). This is a disorder wherein mood changes occur as the winter approaches and episodes of depression are felt during winter. Since the symptoms improve in spring and summer, it is believed that these winter blues are caused due to the lack of sunlight during winters. Certain studies have also established a connection between low vitamin D levels and psychological problems such as bipolar disorders, depression and schizophrenia. Another possible link between depression and the deficiency of this vitamin may be the effect that this sunshine vitamin has on the levels of serotonin. Serotonin is a neurotransmitter that is responsible for the feelings of well-being, relaxation,and calmness. The brain produces more serotonin when the body is exposed to the sun. As night approaches, serotonin is converted into melatonin. Melatonin is a hormone that regulates the sleep cycle. If the body is unable to produce sufficient amounts of melatonin, one's sleep cycle is disturbed. This can cause fatigue and adversely affect one's mood. Causes of a Vitamin D Deficiency The signs of a vitamin deficiency are likely to appear in people who don't follow a healthy diet. Aging also adversely affects the natural process of synthesis of this vitamin by the body. This is why old people must include foods fortified with this vitamin to their diet. Absorption of this vitamin from the dietary sources takes place in the small intestine with the help of bile. If the digestive tract or organs such as liver or kidneys are not functioning properly, then the process of absorption will get affected. The deficiency could also occur, if the body is unable to covert it into the active form. The deficiency of this vitamin could cause musculoskeletal pain or other problems associated with the bones, muscles, and joints. Vitamin D aids in secretion of insulin and improves the sensitivity towards insulin. This is why this nutritional deficiency can make one susceptible to type 2 diabetes. People affected by this deficiency could also experience fatigue, loss of appetite, lowered immunity, or mood swings. There is a lot of speculation regarding the link between vitamin D and depression. Though some studies reveal that sunshine has a good effect on the mood, there could be a variety of other factors that contribute to depression. One cannot, however, ignore the importance of this vitamin. Thus, one needs to make sure that the body's requirement for the sunshine vitamin is met. This can be done by including foods such as milk, egg yolk, fish such as sardines, eel, mackerel, herring, and organ meats. Besides having these food items, spending some time outdoors is definitely a great way for fulfilling the body's need for vitamin D. In severe cases, the use of supplements may prove beneficial for people affected by this vitamin deficiency or seasonal affected disorder. The supplements must be taken as per the prescribed dosage to avoid any side effects.