Some information shows a possible protective effect in vitamin D against the incidence of upper respiratory tract infections (colds). But, a piece of high-profile health news (published in the renowned Journal of the American Medical Association) found that people taking 100,000 IU a month of vitamin D3 did not have a significantly reduced incidence or severity of colds. IU stands for âinternational units,â a measure of the vitamin.
The link between not having enough vitamin D and susceptibility to respiratory tract infections has been unclear, according to background information in the article.
This one comes from New Zealand, where researchers conducted a good-quality study to see if vitamin D supplements actually protected against colds, and also limited how severe they were. It lasted from February 2010 to November 2011, comprising 322 healthy adults. Those individuals in the vitamin D group received an initial dose of 200,000 IU oral vitamin D3, then 200,000 IU one month later, then 100,000 IU each month for a year and a half. The comparison group took placebo.
So, at the beginning of the study, levels of functional vitamin D in the people were 29 nanograms per milliliter (ng/mL). When the supplements kicked in, they increased these levels to a point where they were maintained at more than 48 ng/mL throughout the 18 months.
A key fact: there were 593 upper respiratory tract infections in the supplement group and 611 in the placebo groupâessentially the same.
There was no statistically significant difference between the two groups, with an average of 3.7 infections (vitamin D) and 3.8 (placebo) per person over the 18 months. Also, in both groups, people had colds for the same time span: an average of 12 days. There was no difference in number of days of missed work as a result, or severity of symptoms.
The takeaway message is that, while vitamin D is enormously important on many fronts, taking a monthly dose of 100,000 IU is unlikely to protect you from the common cold or flu. Even during the winter. It remains important to consider vitamin D, however, on a regular basis, and ensure you are getting enough of this nutrient.