Dr. Arianna Carughi
SAB Member, Nutritional Scientist
One of the most important things we can do these days is keep up our vitamin D status (or levels in our blood). Coming up to winter and with “lockdown” and “stay-at-home” orders we should redouble our efforts to obtain vitamin D in our diet. Why? Because studies show that optimal levels of this vitamin appear to protect and improve the time course of difficult-to-treat viral respiratory tract infections such as influenza.
Vitamin D is a fat-soluble vitamin that can be manufactured in our skin upon exposure to sunlight. Some foods like oily fish, eggs and fortified dairy products contain vitamin D but it is difficult to achieve sufficient intake by diet alone. Famously known for its role in building and maintaining strong bones and in calcium absorption, we now know that vitamin D has many other effects in our body, particularly on the immune, nervous and cardiovascular systems.
Vitamin D plays an important immuno-regulatory role in the immune system as it enhances innate immunity and the protective immune responses to respiratory pathogens and boosts the defences of the membranes that line body cavities and passages like those of the respiratory tract.
Large population studies show that low blood levels of vitamin D are linked to higher levels of both viral and bacterial infection. The effect is stronger in individuals with chronic pulmonary disease or asthma. Studies also show that higher vitamin D status is associated with better outcome and time course of the infection.
Looking at the effectiveness of vitamin D supplementation, three large reviews consistently show its benefits for preventing respiratory tract infection, particularly in children. Daily smaller doses of 400 to 1000 IU (or 10 to 25 mcg) appear to be more effective than single large doses. Those individuals that were most vitamin D deficient experienced the greatest benefit. Levels from 1000 to 2000 IU (or 25 mcg to 50 mcg) are known to be safe and beneficial but individuals should not go higher than this unless medically advised to do so, because large doses actually suppress T-cell function.
- Bergman P, Lindh ÅU, Björkhem-Bergman L, Lindh JD. Vitamin D and respiratory tract infections: A systematic review and meta-analysis of randomized controlled trials. PLoS One. 2013;8(6). doi:10.1371/journal.pone.0065835
- Gruber-Bzura BM. Vitamin D and influenza—Prevention or therapy? Int J Mol Sci. 2018;19(8):2419. doi:10.3390/ijms19082419
- Aponte R, Palacios C. Vitamin D for prevention of respiratory tract infections. World Health Organization. http://www.who.int/elena/titles/commentary/vitamind_pneumonia_children/en/. Accessed April 6, 2020.
- Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356. doi:10.1136/bmj.i6583
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