Respiratory tract infections: can vitamin D supplements reduce the risk of getting sick?
Respiratory infections: can vitamin D reduce the risk?
Vitamin D supplements could play a role in preventing respiratory tract infections, reducing the risk of being affected by up to 12 percent. Daily or weekly supplementation with vitamin D appears to be effective especially in individuals with low levels of the vitamin in their blood, prior to treatment. These findings, which will need to be confirmed and further investigated by other studies, suggest the importance of introducing public health measures to increase vitamin D levels in countries where deficiency is very common.
This is the result of research conducted at Queen Mary University of London, and published in the British Medical Journal.
Respiratory tract infections are among the leading causes of hospitalization and mortality
Acute respiratory tract infections affect both the upper and lower airways, causing more or less serious conditions including:
- rhinitis
- sinusitis
- pharyngitis
- pneumonia
- bronchitis
- bronchiolitis
- pertussis
Respiratory tract infections can be caused by bacteria or viruses, which are present in the environment, and are a major cause of hospitalization and mortality worldwide, with more than 2 million deaths in 2013 alone. They are also responsible for nearly 50 percent of doctor visits and hospitalizations in children; in particular, bronchiolitis is the most common cause of hospitalization in the first 12 months of life. Some studies have reported a link between low blood concentrations of 25-hydroxyvitamin D, the main circulating vitamin D metabolite, and susceptibility to acute respiratory tract infections; this molecule and other derivatives of the vitamin would, in fact, be able to induce molecular mechanisms with antimicrobial action.
25-Hydroxyvitamin D appears to promote the activation of certain defense molecules of the immune system in response to attacks by pathogens, viral or bacterial, of 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 tract infections.
For this reason, the team of researchers decided to evaluate the overall effect of vitamin D supplements with respect to the risk of respiratory tract infections and to identify factors that modify this action.
Vitamin D supplements reduce the risk of acute respiratory tract infections
The study conducted by the London researchers compiled data collected from 25 other studies conducted in different countries, which had involved a total of 11,321 participants of all ages. In each of these papers, the effects on participants of treatment, of any duration, with vitamin D3 or vitamin D2 supplements had been observed. After adjusting the data for other potentially influential factors, such as age, sex, and duration of treatment, the results of this meta-analysis revealed that vitamin D supplementation had reduced the risk of infection in all participants. In detail; vitamin D supplementation had resulted in a 12 percent reduction in the percentage of subjects who had had at least one episode of acute respiratory tract infection.
Through subgroup analysis, protective effects were observed especially in subjects who had consumed different amounts, daily or weekly, of vitamin D without additional doses. Among them, the defensive outcomes of supplementation had been greater in those who had, at the start of treatment, low blood levels of 25-hydroxyvitamin D, i.e., less than 25 nanomoles per liter (nmol/L.), than in those with higher levels (≥ 25 nmol/L.). To explain the difference in effects, the authors referred to other previous research that proposed how concentrations of vitamin D that are too high in the circulation after consumption with supplements can deactivate certain enzymes responsible for the synthesis and degradation of its active metabolite, resulting in decreased concentrations in extra-renal tissues.
Such an effect could therefore attenuate the ability of 25-hydroxyvitamin D to support immune responses against respiratory pathogens. The increased efficacy of supplementation in individuals with vitamin D deficiency is based on the principle that people with a deficiency of a micronutrient will be more likely to respond to its introduction. According to the research findings, the use of vitamin D was safe and free of side effects. Potentially adverse reactions were rare, and the risk of such events was the same as for participants who were part of the control group.
A study with some limitations
By the admission of the researchers who conducted it themselves, the study has some limitations, including the difficulty in detecting the effects of vitamin D for some of the groups analyzed. In this regard, in a related editorial, Mark Bolland of the University of Auckland (New Zealand) and Alison Avenell of the University of Aberdeen (UK) question whether this work is really an important new milestone or just another hypothesis that needs confirmation with more research. Indeed, in their opinion, the results obtained are too heterogeneous and insufficiently applicable to the general population.
Vitamin D as a strategy to reduce respiratory tract infections
Despite the doubts highlighted, the researchers point out that in conclusion the data obtained are of high quality and suggest vitamin D supplementation as an effective and safe way to prevent respiratory tract infections. According to the obtained statistical data, those who would benefit most are people with severe vitamin D deficiency.
This reinforces the 'hypothesis of a number of studies that support the introduction of public health measures, such as food fortification, to improve vitamin D status in populations living in areas where insufficiency is very common. Indeed, recall that vitamin D hypovitaminosis is common throughout Europe, especially during winter periods and among certain population groups such as the elderly.
Vitamin D supplements: D3drops
D3drops is a vitamin D3 dietary supplement, manufactured by Omegor, which can be used in all cases of increased need or decreased dietary intake of vitamin D, and, especially in children to ensure normal bone growth and development. Each drop of D3 drops 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