If you have researched more natural ways of relieving the symptoms of chronic urticaria (CU) online, you have perhaps come across the personal accounts of people who have reduced or eliminated hives using vitamin D supplementation. Vitamin D has been on everyone's lips in the last few years, promising to cure or prevent pretty much everything from depression to cancer (not even sparing COVID). This is often accompanied with shady statistics stating that pretty much everyone is vitamin D deficient and that you just can't get enough vitamin D. The idea that a vitamin is the magical cure for everything that ails you isn't new, and it's always raised healthy skepticism in the medical community, for good reasons. So, is there any data to back the claims of people successfully managing their chronic urticaria symptoms with vitamin D supplementation ?
The theory : how could vitamin D help patients with CU ?
In addition to its important role in maintaining bone health, vitamin D also acts as a hormone in the body. It has an important role both on skin health and immune system modulation. In the immune system in particular, it is known to increase the production of factors that promote tolerance of harmless antigens (tolerogenic cytokines), decrease the production of factors that promote inflammation (proinflammatory cytokines), and stabilize mast cells, the cells that release histamine in patients with CU. Tolerogenic cytokines and mast cell stability are key in understanding the causes of allergic diseases such as CU, so there is much interest in researching the relation between vitamin D, its metabolism and these diseases.
The hints : from what observations can we suspect vitamin D could help patients with CU ?
It has been observed that the incidence of acute urticaria episodes follows a seasonal pattern, with higher incidence from winter to spring. Since the main source of vitamin D in the absence of supplementation is often from skin exposure to the sun, blood vitamin D levels also follow this pattern in the population, and are lowest at that time. There are also known genetic variation in the vitamin D receptor, with some that seem to promote allergic diseases. CU has been known for some time to be more prevalent in the first degree relatives of another CU patient than in the general population, which would hint at a genetic cause or risk factor.
Another important clue concerns the relationship between vitamin D deficiency and CU. Studies have shown that :
1) Patients with CU are more likely to be vitamin D deficient
2) People who are vitamin D deficient are more likely to develop CU
This seems to show that vitamin D deficiency is a risk factor for CU, since the correlation goes both ways.
The clinical trials : does vitamin D supplementation actually help patients with CU ?
There have been a few clinical trials aiming at treating CU patients with vitamin D, including a randomized controlled trial performed in the US on 42 CU patients in 2014. All the trials have shown significant improvement of CU symptoms and no reported adverse event. The US study concluded that high dose vitamin D3 (4000 IU / day) could be a safe and effective add-on to CU treatment.
The problem however is that all these studies involve a relatively small number of patients for a maximum of 12 weeks. They also all selected patients with a known vitamin D deficiency, so there is no data on whether CU patients with normal vitamin D levels could benefit from supplementation - which is still possible because the current range for blood vitamin D are based on what is needed for bone health, and individual vitamin D receptor mutations might mean a CU patient who has it needs a higher baseline.
In short, these studies are encouraging, but they do not yield enough data yet to conclude that high doses of vitamin D are safe and effective for patients with CU.
The caveats : can vitamin D supplementation harm you ?
Vitamin D is what is called liposoluble. This means that as opposed to water soluble vitamins like vitamin C, surplus will accumulate in the body. This surplus can become toxic.
There are case studies in the literature of people who have poisoned themselves with vitamin D. In extreme cases, it has caused life-threatening brain swelling. In more moderate cases, it has caused hypercalcemia (high calcium levels in the blood) and kidney stones.
High dose vitamin D supplementation shows promise as a safe treatment for CU, but larger long term studies are needed. If you are vitamin D deficient and have CU, correcting the deficiency might improve CU symptoms. And as with all supplements, the safest way to proceed is to discuss whether it is appropriate in your particular situation with your doctor, especially when it involves vitamins taken at doses higher than generally recommended taken in combination with medication.
Meta-analysis : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8125545/pdf/ijerph-18-04911.pdf
US clinical trial : https://pubmed.ncbi.nlm.nih.gov/24507460/