Respiratory Tract Infections: Can Vitamin D Supplements Reduce Your Risk of Getting Sick?

Respiratory infections: can vitamin D reduce the risk?

Vitamin D supplements might play a role in preventing respiratory tract infections, reducing the risk by up to 12%. Daily or weekly vitamin D supplementation seems especially effective in individuals with low blood vitamin levels before treatment. These results, which need to be confirmed and further investigated by other studies, suggest the importance of implementing public health measures to increase vitamin D levels in countries where deficiency is very common.

This is the outcome of research conducted at Queen Mary University of London, published in the British Medical Journal.

Respiratory tract infections are among the leading causes of hospitalization and mortality 

Acute respiratory infections affect both the upper and lower airways, causing more or less severe conditions including:

• rhinitis
• sinusitis
• pharyngitis
• pneumonia
• bronchitis
• bronchiolitis
• whooping cough

Respiratory tract infections can be caused by bacteria or viruses found in the environment, and represent one of the main causes of hospitalization and mortality worldwide, with over 2 million deaths in 2013 alone. They are also responsible for nearly 50% of medical visits and hospitalizations in children; in particular, bronchiolitis is the most frequent cause of hospital admission in the first 12 months of life. Some studies have reported a link between low blood levels of 25-hydroxyvitamin D, the main circulating metabolite of vitamin D, and susceptibility to acute respiratory infections; this molecule and other vitamin derivatives are thought to induce molecular mechanisms with antimicrobial action. 

25-hydroxyvitamin D seems to promote the activation of certain immune defense molecules in response to attacks by viral or bacterial pathogens in the respiratory tract. Despite knowledge of these mechanisms, previous studies have reported conflicting results on the role of vitamin D supplements in preventing acute respiratory infections. 

For this reason, the research team decided to evaluate the overall effect of vitamin D supplements on the risk of respiratory tract infections and to identify factors that modify this effect.

Vitamin D supplements reduce the risk of acute respiratory infections

The study conducted by the London researchers analyzed data from 25 other studies carried out in different countries, involving a total of 11,321 participants of all ages. Each study observed the effects of treatment, of any duration, with vitamin D3 or vitamin D2 supplements. After adjusting data for other potentially influential factors such as age, sex, and treatment duration, the results of this meta-analysis revealed that vitamin D supplementation reduced infection risk in all participants. Specifically, vitamin D supplementation led to a 12% reduction in the proportion of subjects who had at least one episode of acute respiratory infection. 

Subgroup analysis showed protective effects especially in subjects who consumed varying amounts, daily or weekly, of vitamin D without additional doses. Among these, the protective effects of supplementation were greater in those who began treatment with low blood levels of 25-hydroxyvitamin D, i.e., below 25 nanomoles per liter (nmol/L), compared to those with higher levels (≥ 25 nmol/L). To explain the difference in effects, the authors referred to previous research suggesting that excessively high circulating vitamin D concentrations, after supplementation, can deactivate some enzymes responsible for the synthesis and degradation of its active metabolite, resulting in decreased concentrations in extra-renal tissues. 

Such an effect could therefore reduce the ability of 25-hydroxyvitamin D to support immune responses against respiratory pathogens. The increased efficacy of supplementation in vitamin D-deficient subjects is based on the principle that individuals deficient in a micronutrient are more likely to respond to its introduction. According to the study’s findings, vitamin D use was safe and free of side effects. Potential adverse reactions were rare, and the risk of such events was the same as that of participants in the control group.

A study with some limitations

According to the researchers themselves, the study has some limitations, including difficulty detecting vitamin D effects in some analyzed groups. In a related editorial, Mark Bolland from the University of Auckland (New Zealand) and Alison Avenell from the University of Aberdeen (UK) question whether this work is truly a new important milestone or just another hypothesis that needs confirmation by further research. In their opinion, the results obtained are too heterogeneous and not sufficiently applicable to the general population.

Vitamin D as a strategy to reduce respiratory tract infections

Despite the highlighted doubts, the researchers emphasize that overall the data are of high quality and suggest vitamin D supplementation as an effective and safe way to prevent respiratory tract infections. According to the statistical data obtained, those who would benefit most are people with severe vitamin D deficiencies. 

This supports the hypothesis from a series of studies advocating public health measures, such as food fortification, to improve vitamin D status in populations living in areas where deficiency is very common. It is important to remember that vitamin D deficiency is widespread throughout Europe, especially during winter and among certain population groups such as the elderly.

Vitamin D supplements: D3drops

D3drops is a vitamin D3 dietary supplement produced by Omegor, suitable for cases of increased need or reduced dietary intake of vitamin D, especially in children to ensure normal bone growth and development. Each drop of D3drops provides 400 IU (International Units) of vitamin D3.   

Source: Adrian R Martineau, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 2017;356