Vitamin D, or Calciferol, is an essential fat-soluble hormone required to keep bones, teeth, and muscles healthy by regulating calcium and phosphate levels in the body. It has many other critical functions including reducing inflammation and modulating cell growth, neuromuscular and immune function, and glucose metabolism.
Vitamin D reduces hospitalization of COVID-19 cases
The potential benefits Vitamin D can offer for COVID-19 patients have always been a popular hypothesis for many scientists. However, in a recent non-funded case-control conducted by a team of researchers in the UK, evidence has shown that this is no longer a hypothesis.
Unlike other studies evaluating Vitamin D and its potential benefits in COVID-19 patients, this large retrospective case-control study led by a team from the University of Manchester included 80,670 participants in an attempt to examine the relationship between low vitamin D levels and hospitalizations due to COVID-19. Serum hydroxyvitamin D levels (25(OH)D) were defined as deficient if less than 25 nmol/L, insufficient if between 25 and 50 nmol/L, and sufficient or adequate if greater. The study demonstrates that those with lower serum 25-hydroxyvitamin D levels (<50 nmol/L) are 2.3 to 2.4 times more likely to be hospitalized. Moreover, the study shows that this risk is 2.9 to 3.57 times greater when Serum 25(OH)D is less than 25 nmol/L. Median serum 25(OH)D levels were 50 nmol/L in the nonhospitalized group compared to 35nmol/L in hospitalized patients. However, there was no association identified between vitamin D levels and patient mortality from COVID-19.
The study included two independent cohorts, a primary cohort of 59,368 participants and a validation cohort that included another 21,234. Interestingly, the findings were replicated across these two independent groups which renders this evidence uniquely strong. Despite the unique data it offers, this study had certain limitations, such as its retrospective design and the absence of data for underlying comorbidities that can increase hospitalization risk. Two studies, one in Belgium and another in Switzerland, have also shown similar findings. Another Israeli study of 7,807 subjects demonstrated lower concentrations of Serum 25(OH)D in people tested COVID-19 positive compared to healthy participants. Additionally, vitamin D deficiency (<30 nmol/L) have shown significant association with severity of disease in one Chinese study. On the other hand, a UK Biobank large study found no association between 25(OH)D and risk of COVID-19 infection.
The mechanism by which vitamin D is thought to reduce severity of COVID-19 disease is through modulating the immune system, leaving an effect on macrophage function and innate immunity. Vitamin D is anti-inflammatory, a trait achieved by increasing concentrations of defense peptides. Given such important functions, vitamin D can also clinically reduce the risk of respiratory infections.
Granted the potential beneficial role vitamin D sufficiency plays in improving SARS-CoV-2 status, the study recommends widespread measurement of 25(OH)D to treat cases of deficiency, thereby reducing risk of hospitalization from COVID-19. Such recommendations are very relevant in populations at risk for deficiency.
“In the absence of highly effective prevention and treatment strategies for the pandemic currently, any medical intervention, including vitamin D supplementation/treatment, becomes relevant.”
With that being said, vitamin D cannot act as a replacement for full vaccination. Getting fully vaccinated is prioritized over this recommendation.
Getting enough Vitamin D
Even though Vitamin D is found in some foods, such as oily fish, red meat, and liver, it is predominantly obtained through sun exposure. The ultraviolet rays are responsible for triggering the synthesis through contact with our skin. Through that synthesis process, vitamin D must undergo two hydroxylations in order to reach its activated form, 1,25-dihydroxyvitamin D, or calcitriol. 25-hydroxyvitamin or calcidiol, which is obtained after the first hydroxylation, acts as the best indicator for vitamin D status due to its long half-life. Vitamin D is also available as a dietary supplement.
The recommended intakes differ across many countries due to an incomplete understanding and limited research on the biology and clinical implications of vitamin D. For instance, the FNB committee’s recommended dietary allowances (RDA), sufficient for nutrient requirements, ranges from 600 IU for people 1-70 years of age to 800 IU for older people. On the other hand, The Endocrine Society establishes a requirement of 1,500-2000 IU per day of supplemental vitamin D for adults and 1,000 IU for children. Anyhow, it is very difficult to achieve toxic levels of Vitamin D. The maximum daily intakes unlikely to cause side-effects or the tolerable upper intake levels range from 2,500 IU for those aged 1-3 years to 4,000 IU for those aged 9 years or older. In fact, symptoms of toxicity are still unlikely to occur even at daily intakes below 10,000 IU though not for a long-term period.
One may think that obtaining adequate levels of vitamin D reuires hours of exposure to sunlight; However, experts estimate that only 5 to 30 minutes of daily exposure is sufficient to maintain good vitamin D levels. It is recommended that the time of this exposure be between 10 a.m. and 4 p.m. Ultraviolet light must access the face, hands, arms, and legs without sunscreen and without blocking glass to provide sufficient synthesis. On the other hand, UV radiation can act as a carcinogen, particularly when exposed to at longer time-intervals.
Very few foods contain a decent amount of vitamin D. For example, one table spoon of cod liver oil contains 1,360 IU, 3 ounces of trout or salmon include around 600 IU of vitamin D. Meanwhile, common foods like eggs, liver, beef, tuna fish, cheddar cheese, and sardines contain less than 100 IU per serving. More information regarding Vitamin D content in a variety of food is available on the NIH Vitamin D Fact Sheet.
Conclusion
Vitamin D, an essential nutrient for our health, is associated with a reduced risk of COVID-19 hospitalizations according to a large retrospective case-control study. The study clearly demonstrated that vitamin D insufficiency and deficiency exponentially increase the risk of hospitalizations by a factor of 2.3 to 3.6. This finding provides promising and strong evidence that monitoring and providing supplementation for populations at risk can help reduce the severity of SARS-CoV-2 cases. When natural foods only contain minimal vitamin D, the predominant natural source, sun exposure, and/or dietary supplementation act as an essential requirement for maintaining sufficient vitamin D synthesis.
References:
- Jude EB, Ling SF, Allcock R, Yeap BXY, Pappachan JM. Vitamin D deficiency is associated with higher hospitalisation risk from COVID-19: a retrospective case-control study. J Clin Endocrinol Metab. 2021 June
- NIH Vitamin D Fact Sheet.
Written by Zein Hanouneh
Zeintific 