Multiple articles have been published about Vitamin D in the past several years. Here is a review of the information that is known and speculated about Vitamin D.
Vitamin D is a fat soluble vitamin that is naturally present in a few foods: fatty fish (e.g., salmon, tuna and mackerel), fish liver oils (e.g., cod liver oil), shitake mushrooms and egg yolks. Foods that are fortified with Vitamin D include milk and grains (bread, pasta, etc.). It is also produced in the body when sunlight rays strike the skin and trigger the body to make vitamin D. Exposure to sunlight 2 x weekly, 5-30 minutes is recommended for sunlight syntheses of vitamin D. Conditions that limit synthesis include sunscreen (greater than SPF 8), pollution, glass, cloud cover, and dark skin. Latitude may not bear as much importance as previously assumed. A recent study found 14 % of children in the southwestern USA deficient in Vitamin D.
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal bone health. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Together with calcium, vitamin D also helps protect older adults from osteoporosis. Vitamin D's modulates cell growth, neuromuscular and immune functions, and helps reduce inflammation. Vitamin D modulates genes which encode proteins that regulate cell proliferation, differentiation, and cell death. Many cells have vitamin D receptors, including a more recent discovery that there are vitamin D receptors in the brain. A recent small study showed Vitamin D deficiency more prevalent in children with serious mental illness. Emerging research suggests a possible role of Vitamin D in protecting against cancer, heart disease, fractures and falls, autoimmune disease, influenza, type 2 diabetes and depression.
A common reason that a child is deficient in Vitamin D is a lack of adequate intake of Vitamin D through food. A nutritionist estimated that a child 1-13 years old would need to drink six cups of milk or 15 servings of cereal that has been fortified with vitamin D daily to meet the recommended 600 IU's per day. Other reasons for deficiencies in Vitamin D include infants that are breast fed, limited exposure to sunlight, dark skin, and gastrointestinal conditions that impair the absorption of Vitamin D.
Vitamin D 3 (cholecalciferol) is the preferred form of supplementation. It should be taken with a snack or meal that contains fat. Fat soluble vitamins are better absorbed in the presence of fat. Blood serum levels can be done to check vitamin D levels. The recommended test is 25 (OH) D. Blood levels below 30 nmol/L (12ng/ml) are considered deficient.
In 2009 the Institute of Medicine recommended the following supplement schedule of Vitamin D: Age 0-12 mo, 400 IU's/day, 1-18 years old, 600 IU's/day. Other publications have written the following for Vitamin D supplementation:Adequate Intake:Birth to 18 ug/d = 200 IU; Upper Intake; 1-18 years 25 ug/d = 1000 IU. Vitamin D toxicity appears to occur from excess supplements