Vitamin D and Immunity: What You Need To Know
An intriguing new theory suggests that diminished winter blood levels of vitamin D increase people's susceptibility to influenza infection. Patients supplemented with vitamin D were shown to be completely protected against influenza infection, even while living in close proximity to people infected with flu.
Vitamin D has far-ranging effects on the immune system. Dangerous flu virus strains stimulate white blood cells to produce inflammatory cytokines associated with severe illness, while vitamin D protects against this effect. Vitamin D enhances the production of antimicrobial peptides, which are proteins that protect organisms from infection-causing microbes such as viruses. Vitamin D also activates essential infection-fighting immune cells known as macrophages.
People who live at higher latitudes, where less vitamin D is available from exposure to sunlight, experience a greater risk of illnesses such as multiple sclerosis, diabetes, osteoporosis, and certain cancers.
People seeking to optimize immune health and protect against viral flu infections, particularly elderly adults, should consider supplementing with high-dose vitamin D, especially during the winter months.
Vitamin D Dosage Suggestions
While the U.S. recommended dietary allowance (RDA) for vitamin D is 400 IU per day, (25) many health authorities now recommend consuming 800 IU or more of vitamin D daily. (26)
Research suggests that the elderly in particular may benefit from higher vitamin D doses such as 2000 IU daily—and perhaps even up to 5000 IU daily—for optimal effects. Studies suggest that a healthy serum level of vitamin D (25-hydroxyvitamin D) is 75–125 nmol/L. (27)
Research published since 1997 suggests that vitamin D toxicity is very unlikely in healthy individuals at intake levels lower than 10,000 IU/day. (28-30) Any individual taking high doses of vitamin D should be monitored for signs and symptoms of vitamin D toxicity.
Vitamin D toxicity can cause symptoms such as nausea, vomiting, poor appetite, constipation, and weakness, and signs that include heart arrhythmias, kidney stones, and elevated blood levels of cholesterol, calcium, or liver enzymes. (25,26)
Vitamin D is contraindicated in individuals with hypercalcemia (high blood calcium levels). (25,26)
People with kidney disease and those who use digoxin or other cardiac glycoside drugs should consult a physician before using supplemental vitamin D. (25,26)
25 Available at pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/vit_0265.shtml. Accessed November 6, 2006.
26 Meletis CD. Vitamin D. Cancer prevention and other new uses. Life Extension. March, 2006:50-58.
27 Holick MF. Vitamin D deficiency: what a pain it is. Mayo Clin Proc. 2003 Dec;78(12):1457-9.
28 Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. 1999 May;69(5):842-56.
29 Vieth R, Chan PC, MacFarlane GD. Efficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level.
Am J Clin Nutr. 2001 Feb;73(2):288-94.
30 Heaney RP, Davies KM, Chen TC, Holick MF, Barger-Lux MJ. Human serum 25-hydroxycholecalciferol response to extended oral dosing
with cholecalciferol. Am J Clin Nutr. 2003 Jan;77(1):204-10.
Excerpt from Life Extension web report lefcms.lef.org/magazine/mag2007/feb2007_report_vitamind_01, issued February 2007. Life Extension is a global authority on health, wellness, and nutrition as well as a respected provider of scientific information on disease prevention.