Vitamin D (ergocalciferol or calciferol) is a fat-soluble vital nutrient needed by our body to build and maintain healthy bones. It supports our muscles, brain cells, and immune system due to its anti-inflammatory, antioxidant, and neuroprotective properties. Vitamin D is mainly made in the skin by exposure to sunlight, where sunlight converts a chemical in the skin to the form of a vitamin called calciferol. Bodies make vitamin D based on skin color, geographic region, air pollution, and other factors. Vitamin D deficiency can lead to chronic fatigue, scientifically known as Myalgic encephalomyelitis. Studies suggest that vitamin D supplements can improve blood pressure, endothelial functions, and reduce cardiovascular disease risk, potentially reducing the severity of fatigue.

Vitamin D deficiency is linked to increased autoimmunity and susceptibility to infection. Supplementing Vitamin D can benefit people with autoimmune diseases like multiple sclerosis (MS), rheumatoid arthritis (RA), diabetes mellitus (DM), inflammatory bowel disease, and systemic lupus erythematosus (SLE). Vitamin D affects cells within the immune system, inhibiting B cell (a type of white blood cell called lymphocytes) proliferation, blocking B cell differentiation, and suppressing T cell proliferation (T cell is a type of white blood cell that develops from stem cells in the bone marrow).

The treatment involves taking supplements like ergocalciferol or calciferol, with the dose based on age, severity, and other medical conditions. High doses may be given initially to normalize levels, followed by a maintenance dose. Natural vitamins can be produced by sun exposure for 20-30 minutes, 2-3 times a week. Other sources include foods like egg yolk, cod liver oil, red meat, liver, sardines, tuna, and salmon. For children, liquids and drops are available. When vitamin D deficiency occurs, the condition is treated with vitamin D supplements, and given enough fortified food and drinks such as milk, cereal, fatty fish, and sardines.