Ready for an unpopular opinion?
Forget the vitamin D when it comes to preventing COVID-19.
There are a ton of recommendations circulating online promoting the use of vitamin D in preventing and treating COVID-19. It seems reasonable that people would recommend this, as we know that low levels of vitamin D are associated with poor health and more respiratory infections. Finally, we know that Vitamin D has a variety of effects on the immune system.
However, I've got my doubts.
I’m sharing my unpopular opinion for a few reasons:
1. The published literature is not at all clear if giving Vitamin D is helpful in preventing respiratory infections.
2. Some patients are taking too much vitamin D and doing themselves harm.
3.There are better options from a preventative standpoint.
Can Vitamin D supplementation prevent respiratory infections?
The evidence on the role of vitamin D on preventing respiratory infections is mixed. Some reviews do suggest benefit, but an equal number show no effect. As this analysis wrote:
“A total of five aggregate data meta-analyses incorporating data from up to 15 primary trials have been conducted to date, of which two report statistically significant protective effects, and three report no statistically significant effects. (1)”
When strong clinical effects are present, what happens is that as more studies are done, there is a large amount of agreement and the evidence piles up on one side. When an intervention doesn’t work as well, as in this example, we see a mixed picture.
Researchers have been interested in this question for a long time and there are a lot of studies to look at. If Vitamin D had a hugely helpful effect, we would know it. Unfortunately, when we take the big picture view of the evidence, Vitamin D just doesn’t have a big role to play in preventing respiratory infections.
What is the evidence against Vitamin D ?
Dr. Alan Gaby, a pioneer in Integrative and Nutritional medicine, (yes, he actually wrote the book) wrote the following in an editorial for Townsend Letter:
“Contrary to these claims, I have argued on numerous occasions that using large doses of vitamin D for the sole purpose of achieving an “optimal” serum 25(OH)D level has not been demonstrated to be safe or effective. The idea that we should aim for 25(OH)D levels of 36-40 ng/mL or higher is based almost entirely on observational studies, which found that these levels were associated with better health outcomes. However, associations do not prove causation. A growing body of evidence from randomized controlled trials indicates one of the following: 1) high doses of vitamin D are not more effective, and may actually be less effective in some instances, than moderate doses of the vitamin, or 2) high doses of vitamin D are not more effective than placebo (2).”
First, let’s look at a well done study was published in JAMA and looked at giving healthy children in Toronto either a high dose of vitamin D or a standard dose during cold and flu season (3). They then observed the number of infections in each group - there was no difference.
"These findings do not support the routine use of high-dose vitamin D supplementation in children for the prevention of viral upper respiratory tract infections."
Next, the PODA Trial showed that vitamin D supplementation in older African American Women did not prevent acute respiratory infections (4). This was a group of 260 women who were followed for three years.
Finally, we also have a study of 5,110 New Zealand adults were given monthly doses of vitamin D and compared against a placebo group (5). They were followed for three years. The treatment group had vitamin D levels that rose to 54.1 compared to 26.4 in the placebo group. The researchers concluded:
“Monthly high-dose vitamin D supplementation does not prevent ARI in older adults with a low prevalence of profound vitamin D deficiency at baseline.”
Is there evidence that too much vitamin D can be a bad thing?
Unfortunately, yes there is.
On this very topic, some studies have shown that supplementation with vitamin D is associated with higher rates of respiratory infections. A study of high dose vitamin D was associated with increased risk and duration of upper respiratory infections in a group of patients in the UK (6).
Other potential risks are that high dose vitamin D may actually lead to an increase in falls in older adults (7).
There is emerging evidence that high dose vitamin D supplementation might be harmful in cardiovascular disease and atherosclerosis (8).
“Notably, some cohort studies and a recent RCT provide evidence for harmful effects of vitamin D on CVD outcomes at 25(OH)D levels in excess of 100 nmol/l .”
What happens when the vitamin D is pushed up high is that it encourages the body to absorb extra calcium even if it isn’t needed. If the body is is unable to use all that extra calcium it will make its way into several unhelpful places like joints (causing arthritis) and blood vessels (contributing to heart disease). I often use a scan called a coronary calcium score, which measures the presence of calcium in the arteries as a marker for heart disease. Extra calcium in the arteries is highly associated with coronary artery disease. Let’s not put more calcium in our arteries than is needed, okay?
I have seen vitamin D supplementation cause elevated calcium levels in several patients who came to work with me. I once had a patient come in who was taking 37,000 IU of vitamin D daily for over a year because a well-meaning but clueless practitioner didn’t think to add up the vitamin D in all the various supplements she was recommending.
Anything else?
I don’t have a secret agenda against vitamin D. I often recommend low dose vitamin D supplementation to my patients when they are are deficient, but rarely find a need to give more than 2,000 IU a day. (I do think it is important to use a supplement that also includes vitamin K2, but that’s a story for another day.)
What I observe is that vitamin D levels in the blood are often a marker of poor health rather than a marker of deficiency in the tissues. I have observed several patients who improved their diet, sleep and nutrition habits, and their vitamin D levels improved to normal in a matter of weeks, without supplementation.
In this case, I don’t think there is strong evidence for using vitamin D to prevent viral infections, especially COVID-19. I would much rather have my patients focus on optimizing their sleep, stress and nutrition habits. I’ll talk about supplements that are more likely to be helpful in a future post.
Would you like more information, or to schedule an appointment?
References:
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:i6583. Published 2017 Feb 15. doi:10.1136/bmj.i6583
Gaby, Alan. Concerns About High Dose Vitamin D. Townsend Letter. January 2018.
Aglipay M, Birken CS, Parkin PC, et al. Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children. JAMA. 2017;318(3):245–254. doi:10.1001/jama.2017.8708
Aloia JF, Islam S, Mikhail M. Vitamin D and Acute Respiratory Infections-The PODA Trial. Open Forum Infectious Diseases. 2019 Sep;6(9):ofz228. DOI: 10.1093/ofid/ofz228.
Camargo CA, Sluyter J, Stewart AW, et al. Effect of monthly high-dose vitamin D supplementation on acute respiratory infections in older adults: A randomized controlled trial [published online ahead of print, 2019 Aug 17]. Clin Infect Dis. 2019;ciz801. doi:10.1093/cid/ciz801
Martineau AR, Hanifa Y, Witt KD, et al. Double-blind randomised controlled trial of vitamin D3 supplementation for the prevention of acute respiratory infection in older adults and their carers (ViDiFlu). Thorax. 2015;70(10):953–960. doi:10.1136/thoraxjnl-2015-206996
Guirguis-Blake JM, Michael YL, Perdue LA, Coppola EL, Beil TL. Interventions to Prevent Falls in Older Adults: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA. 2018;319(16):1705–1716. doi:10.1001/jama.2017.21962
Zittermann A. Vitamin D Status, Supplementation and Cardiovascular Disease. Anticancer Res. 2018;38(2):1179–1186. doi:10.21873/anticanres.12338