Vitamin D protects against common cold and flu

A group of researchers at the Queen Mary University of London (QMUL) showed through a meta-analysis that Vitamin D protects against acute respiratory tract infections (ARIs). Those who are lacking Vitamin D and those not receiving bolus doses, a quantity of fluid or medication given intravenously at a controlled, rapid rate, benefit the most.

ARIs are a major cause for global mortality. They were responsible for an estimated 2.65 million deaths in 2013, according to the Global Burden of Disease (GBD), and 10 percent of ambulatory and emergency visits in the USA, according to a study conducted by Carlos Grijalva of the Vanderbilt University School of Medicine.

ARIs are divided into two subcategories: upper respiratory tract infections (URIs) and lower respiratory tract infections (LRIs). The upper part of the respiratory tract starts from the airways of the nostrils to the vocals cords in the larynx. Common infections include rhinitis (the common cold) and the flu.

The lower part of the respiratory tract continues from the trachea and bronchi and ends at the bronchioles and the alveoli. Typical forms of infections consist of pneumonia and bronchitis.

This meta-analysis study evaluated data for 10,933 participants in 25 randomized controlled experiments done in 14 different counties, including the U.S., Japan, New Zealand and Sweden.

“This major collaborative research effort has yielded the first definitive evidence that Vitamin D really does protect against respiratory infections,” Professor Adrian Martineau of QMUL, the leading researcher in this study, said in a press release. “Our analysis of pooled raw data from each of the 10,933 trial participants allowed us to address the thorny question of why Vitamin D ‘worked’ in some trials, but not in others.”

Vitamin D, the sunshine vitamin, is known to increase antimicrobial peptides in the lungs to combat invading viruses and bacteria. According to Martineau, Vitamin D is also known to induce cell self-degradation and the synthesis of reactive nitrogen and oxygen intermediates.

Several observational studies have indicated a relationship between ARIs and Vitamin D, yet of the other five meta-analyses to date, only two studies report that Vitamin D supplements have significant effect in decreasing the risk for ARIs.

Martineau and his team suggested the cause of conflicting results is due to various Vitamin D levels and use of bolus doses. Those who had the lowest Vitamin D levels benefited the most whereas those with higher levels benefited less.

They proposed that the reason why the bolus doses were ineffective against ARIs is because of the wide fluctuations in the 25-hydroxyvitamin D concentration. 25-hydroxyvitamin D is the major circulating Vitamin D metabolite, a compound that is formed from Vitamin D metabolism.

The results of this study provide evidence that could aid the introduction of public health policies.

“By demonstrating this new benefit of Vitamin D, our study strengthens the case for introducing food fortification to improve Vitamin D levels in countries such as the UK where profound Vitamin D deficiency is common,” Martineau said.

In addition, the results could potentially explain the observation that the cold and flu are the most common during the winter due to fewer hours of sunshine. Vitamin D could also be potentially helpful against asthma attacks, which are caused by respiratory viruses.