By Dr. Meghan Bauer ND
Vitamin D has a chemical structure like a hormone yet it’s classified as a vitamin. We can make it from a reaction in our skin with the sun and we can eat it as a nutrient (food and supplement). If this sounds like a riddle it’s because it is. Vitamin D has long been known for its necessity in absorption and retention of calcium and phosphorus for our bones but we find receptors for the vitamin throughout our bodies.
In recent years, researchers have been trying to unravel the full picture of Vitamin D and what we need it/use it for. So far we know that it is involved in cardiovascular health, cognitive health, bone health, cancer survivorship, improved outcomes in individuals with diabetes type II, autoimmune diseases like MS, control of inflammation and in general immune health.
A large scale review of all of the literature on Vitamin D was done in 2014 and the authors concluded that “Despite a few hundred systematic reviews and meta-analyses, highly convincing evidence of a clear role of vitamin D does not exist for any outcome, but associations with a selection of outcomes are probable” [10].
One area where the research is more robust and conclusive is with Vitamin D and our immune system, in particular it’s been well studied for its relationship with the common cold and the flu. Here’s a brief run down of the connections we have evidence for as it relates to the role of Vitamin D and the common cold and flus:
- Vitamin D levels are lowest in the winter months [1].
- The active form of vitamin D, D3, tempers the damaging inflammatory response of some white blood cells, while it also boosts immune cells’ production of microbe-fighting proteins [1].
- Children who have vitamin D-deficiency rickets are more likely to get respiratory infections, while children exposed to sunlight seem to have fewer respiratory infections [1].
- Adults who have low vitamin D levels are more likely to report having had a recent cough, cold, or upper respiratory tract infection [2].
- A large meta-analysis of individual participant data indicated that daily or weekly vitamin D supplementation lowers risk of acute respiratory infections. [4] This effect was particularly prominent for very deficient individuals.
- The findings from this large meta-analysis have raised the possibility that low vitamin D levels may also increase risk of or severity of novel coronavirus 2019 (COVID-19) infection. Although there is no direct evidence on this issue because this such a new disease, avoiding low levels of vitamin D makes sense for this and other reasons [4].
- A Systematic Review in October, 2022 concluded that: “Vitamin D supplementation is effective in reducing the COVID-19 severity. Hence, vitamin D should be recommended as an adjuvant therapy for COVID-19.However, more robust and larger trials are required to substantiate it further” [9].
An interesting randomized controlled trial in Japanese school children tested whether taking daily vitamin D supplements would prevent seasonal flu. The trial followed nearly 340 children for four months during the height of the winter flu season. Half of the study participants received pills that contained 1,200 IU of vitamin D; the other half received placebo pills. Researchers found that type A influenza rates in the vitamin D group were about 40% lower than in the placebo group; there was no significant difference in type B influenza rates.
Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. The American journal of clinical nutrition. 2010 May 1;91(5):1255-60.
Even without all of the details of how Vitamin D is working we have been able to understand that avoiding a vitamin D deficiency is key for overall health. Vitamin D is often the most common supplement that I see patients taking however I routinely see low levels of Vitamin D on testing. Make sure to get your levels tested and supplement accordingly.
The recommended daily intake is 600 – 800 IU’s/day however more is often needed to climb out of a deficiency. Please check with your health care providers for your best dosing strategy!
References (some of many!)
- Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, Garland CF, Giovannucci E. Epidemic influenza and vitamin D. Epidemiology & Infection. 2006 Dec;134(6):1129-40.
2. Ginde AA, Mansbach JM, Camargo CA. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Archives of internal medicine. 2009 Feb 23;169(4):384-90.
3. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. The American journal of clinical nutrition. 2010 May 1;91(5):1255-60.
4. Martineau AR, Jolliffe DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, Dubnov-Raz G, Esposito S, Ganmaa D, Ginde AA, Goodall EC. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017 Feb 15;356:i6583.
5. Zasloff M. Fighting infections with vitamin D. Nature medicine. 2006 Apr;12(4):388-90.
6. Nnoaham KE, Clarke A. Low serum vitamin D levels and tuberculosis: a systematic review and meta-analysis. International journal of epidemiology. 2008 Feb 1;37(1):113-9.
7. Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Archives of internal medicine. 2007 Sep 10;167(16):1730-7.
8. Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004; 79:362-71
9. Shah K. Does Vitamin D Supplementation Reduce COVID-19 Severity?: a systematic review. QJM. 2022 Oct 25; 115(10): 665 – 672.
10. Theodorateu E. et al. Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomized trials. BMJ. 2014 April 1; 348.