Upper respiratory tract infections (URTI’s) account for one of the main reasons for doctor visits.  It is estimated that adults have, on average, between 2-4 URTI’s per year.  This number is greater for children.  While vitamin C is widely accepted as having a preventative effect on colds and flu, vitamin D is quickly gaining ground!

A recent study from the Archives of Internal Medicine’s February 23, 2009 Issue [Ginde et al] associates higher vitamin D levels (serum 25(OH)D) with a reduction in the incidence of upper respiratory tract infection.

Based on 18 883 participants, the study showed that a recent URTI was reported by 24% of the individuals with vitamin D levels below 10ng/mL as compared to 17% by those whose levels were 30ng/mL or more.

“In this study, we also found that individuals with respiratory tract diseases (i.e. asthma and COPD) are of particular interest.  Effect modification by asthma and possibly COPD, on the association between serum 25(OH)D level and recent URTI indicates that the role of vitamin D may be of greater importance for individuals with these common conditions.”

“Randomized controlled trials of higher-dose vitamin D supplementation (>=1000IU/d), particularly in the winter season, at higher latitudes, and for individuals with respiratory tract diseases, will help clarify the role of vitamin D supplementation in the reduction of RTI.”

“In conclusion, serum 25(OH)D levels have an independent inverse association with recent URTI.  Although 25(OH)D levels less than 30ng/mL and URTI were higher in the winter season, the inverse association was present throughout the year.  [ ] Vitamin D supplementation may reduce the incidence of URTI and exacerbations of respiratory tract diseases.”

While Vitamin D is present in some foods, sun exposure or supplementation is necessary to obtain adequate daily amounts.  It is a fat soluble vitamin found in foods including butter, fortified milk, eggs, liver, and fatty fish.

Vitamin D supplements should be taken with food.  Other fat soluble vitamins include vitamins A, E and K.

There are two forms of vitamin D: vitamin D2 ‘ergocalciferol’ and vitamin D3 ‘cholecalciferol’.  Vitamin D2 is more commonly found in supplements.  It was believed that vitamin D3 was more potent than vitamin D2.  However, a December 10, 2007 randomized, placebo-controlled, double-blinded study conducted in Boston suggests that these vitamin subtypes are equally effective (The Journal Of Clinical Endocrinology & Metabolism; M.F. Holick et al.):

“1,000 IU of vitamin D2 daily was as effective as 1,000 IU of vitamin D3 in maintaining serum 25-hydroxyvitamin D levels and did not negatively influence serum 25-hydroxyvitamin D3 levels. Therefore, vitamin D2 is equally as effective as vitamin D3 in maintaining 25-hydroxyvitamin D status.”

Involved in calcium absorption and metabolism, vitamin D supplementation is used to prevent or manage osteoporosis, osteomalacia and rickets.  It also appears to be protective against cancer, and has other therapeutic uses such as the treatment of psoriasis.  Vitamin D is currently being researched for its effects on multiple sclerosis. Supplementation is particularly important for breast-fed infants, as breastmilk is typically deficient in vitamin D.  Breast-feeding mothers should consider testing their levels of Vitamin D.

Canadian Cancer Society currently recommends 1000 IUD, however the RDA is currently 400IUD.  There is pressure to increase the RDA. Supplementation has greater importance in the winter months and for those living in the north.

Toxicity is a consideration.  While sun exposure will not lead to excess vitamin D, it is possible to overdose on supplements.  In infants, large doses of vitamin D have been linked to nausea, vomiting, high blood pressure, and kidney problems.

Vitamin D levels are being tested more often.  It is necessary to fast for four hours prior to having this blood test performed.