Vitamin D has received increased attention due to its crucial role in disease prevention and immune response.
People deficient in vitamin D who don't get enough sun may need to supplement, particularly during winter months. D3 or cholecalciferol is the recommended form and in sufficient amounts to make a difference in maintaining health or treating illness.
Natural Swine Flu Prevention & Treatment: Vitamin D
Most vitamin D is created from exposure to UV-B radiation from the sun. As a result, vitamin D deficiency is more common in the winter, when cold and flu levels reach their peak in populations. The rapid spread of the flu usually stops by May when population 25(OH) D levels quickly rise.
A large study appearing in the February 2009 Archives of Internal Medicine found that people with the lowest blood vitamin D levels reported having more recent colds or flu. The risks rose in adults and children who had acute or chronic respiratory disorders. "The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu," says Adit Ginde, MD, MPH, UC Denver Division of Emergency Medicine and lead author of the study.
How Vitamin D Fights Colds and Flu
The body's immune system naturally produces antimicrobial, (destroying or inhibiting the growth of microorganisms), peptides or (AMPs). These AMPs won't work with every virus it comes in contact with, but for the ones they do, the body's immune system automatically springs into action.
When microbes like the influenza virus reach upper respiratory airways, they stimulate the production of an enzyme that converts 25(OH)D, the circulating inactive form of vitamin D, into the hormonally active 1,25(OH)2D (1,25-dihydroxyvitamin D). 1,25(OH)2D is needed to activate the genes that produce antimicrobial peptides.
Ref: http://www.suite101.com/content/swine-flu-prevention-requires-optimal-vitamin-d-a161231 
Swine Flu Deaths in Children and Vitamin D Deficiency
A 2009 report in the Journal of Pediatric Research stated that infants and children appear more susceptible to viral rather than bacterial infections when they are deficient in vitamin D. Based on the available evidence connecting vitamin D, infections and immune function in children, researchers suggest vitamin D supplementation may be a useful therapy in pediatric medicine.
Dr. Cannell a leader in the field of vitamin D research, published his findings on the seasonality of the flu and vitamin D deficiency in 2006 in a study "Epidemic influenza and vitamin D". Results indicate that vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation exposure on the skin (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children.
A large study reported in the February 2009 Archives of Internal Medicine found that people with the lowest blood vitamin D levels reported having more recent colds or flu. Risk rose in adults and children with acute or chronic respiratory disorders. "The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu," says Adit Ginde, MD, MPH, UC Denver Division of Emergency Medicine and lead author of the study.
Dr. Mercola, a leading natural health advocate notes in his online article "Anti-Vitamin D Bias, CDC Stumbles on Deficiency Link to H1N1 Deaths," that while several of the children who died of the swine flu did have neurodevelopment issues, many of these conditions are associated with childhood vitamin D deficiency. In addition, these neurodevelopment conditions are often treated with anti-convulsant drugs which further lower D levels.
Optimal Vitamin D Levels
Despite the name, vitamin D isn't a vitamin; it's a secosteroid hormone that targets over 2000 genes in the human body. Vitamin D has been shown, according to the Vitamin D Council, to have a positive effect on bone health, immunity, cancer prevention and inflammation. Vitamin D not readily available in most foods. It is made in large quantities when sunlight strikes bare skin, which is why a deficiency is more common in the winter, when sunlight is less available. Colds and flu levels also reach their peak in populations during the winter months.
Vitamin D deficiency in American teens is common. One study indicates that only 25 percent of more than 3,500 teenagers ages 12 to 19 had levels higher than 26 ng/ml, and 25 percent had levels lower than 15 ng/ml which is severely deficient. The optimal level of vitamin D is much higher than the conventional recommendation of 30 ng/m. Vitamin D levels should be 50-65 ng/ml.
"If you use suntan parlors once a week," says Dr. Cannell, "or if you live in Florida and sunbathe once a week, year-round, do nothing." However, if you receive very little UVB exposure the Council recommends the following dosing levels of D3 for healthy adults and children:
- healthy children under the age of 2 - 1,000 IU per day*
- healthy children over the age of 2 - 2,000 IU per day*
- adults and adolescents - 5,000 IU per day.
*The American Academy of Pediatrics recommends 400 mg per day for children.
Dr. Cannell suggests increasing the dose if your child is ill although there is really no way to know if they are at optimal levels unless they are tested. He recommends supplementing before getting the 25(OH)D test blood test then adjusting the dose so your child's 25(OH)D levels are between 5080 ng/ml, summer and winter.
Studies show that vitamin D stimulates the immune system and disease-fighting cells, called macrophages and T cells. The cells create proteins that have antiviral and antimicrobial properties. Further, we know that macrophages and T cells have vitamin D receptors (VDRs) on them, enhancing their functions. Dr. Cannell became interested in vitamin D research when he noted that patients in his psychiatric ward who took 2,000 IU of vitamin D did not get the flu, while the patients in other wards (who did not take vitamin D) did. The patients intermingled with each other so cross exposure was certain. The study showed that vitamin D supplementation could prevent one from developing the flu.
