Spring is just around the corner, and the winter flu season is on its way out. However, we are still dealing with some aspects of the COVID-19 pandemic with the Omicron variant. Protecting and boosting your immune system is still important.
Vitamin D plays a key role in keeping your immune system strong to help fight against respiratory infections. Vitamin D is a fat-soluble vitamin that you need for immune function, brain, muscle, bone, and mental health. Even though vitamin D is so important to our health, most of the American population is deficient in this crucial vitamin.
Let’s take a deeper look at what vitamin D is, how it and your immune system work together, vitamin D levels and viral infections, and vitamin D and the flu.
What is Vitamin D?
Vitamin D is a fat-soluble vitamin your body needs to function well. It is vital for your immune function, bone and muscle health, brain function, and mental health as well as other health issues.
When the sun’s ultraviolet (UV) rays reach your skin, it initiates vitamin D synthesis in your body. This is the optimum way to obtain your vitamin D needs. You can also obtain vitamin D by consuming fatty fish, such as tuna, salmon, and mackerel, beef liver, egg yolks, and mushrooms.
Still, these two methods may fall short in providing you with adequate levels of vitamin D. Many of us do not get enough healthy sun exposure. We work and live indoors. And, many of us live in areas with weather conditions that limit sun exposure, like the northern parts of the United States, Canada, and Alaska. This gives even greater importance to supplement with vitamin D to maintain optimal levels and protect your health.
How does Vitamin D work?
When your vitamin D comes from sunshine or food, it will undergo two hydroxylations to become activated and available for use by your body. The first hydroxylation happens inside your liver where vitamin D converts into 25-hydroxyvitamin D (25(OH)D) or calcidiol.
After this, the second hydroxylation occurs in your kidneys. There it can convert into 1,25-dihydroxy vitamin D (1,25(OH)2D), or calcitriol, which is a physiologically active form of vitamin D your body needs that interacts with the VDR receptor on the cells of the body.
This active form of vitamin D is necessary for optimal phosphate concentration and serum calcium levels. It supports bone mineralization, bone strength, and bone growth. Vitamin D may lower the risk of muscle cramps, muscle spasms, osteomalacia, and osteoporosis. In addition, it supports cellular metabolism, immune health, cellular growth, and neuromuscular function.
Vitamin D and immune function
Vitamin D plays a key role in your innate and adaptive immune responses. It plays a key role in maintaining immune homeostasis, and it is an immunomodulator that targets B-lymphocytes, T- lymphocytes, and immune cells like macrophages, monocytes, and dendritic cells. Vitamin D deficiency increases the risk of autoimmune disorders and chronic infections.
In addition, the active metabolite of vitamin D, 1,25(OH)2D is an active player when it comes to immune function, immune regulation, and the health of your innate and adaptive immune system. Vitamin D deficiency thus may increase the risk and symptoms of immune dysfunction. Low levels of vitamin D may raise the risk of autoimmune disorders such as multiple sclerosis and type 1 diabetes. Deficiency in vitamin D increases the risks and outcomes of infectious diseases.
Studies suggest that vitamin D deficiency increases the risk of tuberculosis and respiratory infections. Other studies show that adequate levels of vitamin D may decrease the risk of viral influenza infections like the flu and COVID-19.
Vitamin D receptors are expressed on your immune cells, including antigen-presenting cells, B cells, and T cells. This can impact your innate and adaptive immune response and lower your risk of infections and autoimmune issues.
A 2020 study found that vitamin D may play a crucial role in your immune health. According to the researchers, 1,25(OH)2D may increase autophagy in your body. This may support your body in fighting respiratory infections. It can mediate T-cell responses, lower inflammation, and even offer antiviral and antibacterial benefits.
Vitamin D and viral infections
Vitamin D plays an essential role in fighting against viral infections. It may help to modulate your immune system to reduce your risks, support recovery, and stop viral infections.
Researchers found that vitamin D deficiency is common among people with viral infections, including influenza, COVID-19, hepatitis, and HIV/AIDS. They found that vitamin D helps to regulate the innate and the adaptive immune system, offers anti-viral properties, and may reduce the risk of infections.
A 2019 meta-analysis analyzed individual participant data and has found that vitamin D supplementation may help to prevent acute respiratory infections. A 2020 review found that vitamin D may have immune-modulatory benefits on viral infections.
A 2021 article found that vitamin D plays a role in immune protection. It may help to reduce inflammation, decrease the risk of tissue damage, and may offer an antiviral immune response. The study suggested that vitamin D may be beneficial for those with COVID-19 as deficiencies in vitamin D have been linked to increased risk of severe disease and mortality.
Studies on Vitamin D and flu
Every year, we face the flu season, so it’s critical that you support your immune system year-round to help your body through this season. The effects of vitamin D on the flu virus have been studied extensively. Here are just a few of those studies and their results.
A 2020 review found that vitamin D may reduce the risk of respiratory infection, serious illness, and death in both influenza (the flu) and COVID-19. According to the review, vitamin D may decrease the concentration of inflammatory cytokines and as a result may lower the risk of lung infections, pneumonia, and ARDS.
Researchers found that vitamin D deficiencies are common in chronic diseases and health issues that increase the risk of complications for the flu and COVID-19. The authors of the review recommend 10,000 IU/dL of vitamin D during the initial phase of the infection followed by 5,000 IU/dL after a few weeks with a goal to achieve 40 – 60 ng/mL 25(OH)D.
A 2021 paper found that sunlight, which increases vitamin D production and vitamin D levels, may reduce the risk of the flu. Researchers found that the relationship between sunlight and influenza respiratory infections was one of the main driving factors during the H1N1 epidemic in 2009.
They found that about a 10 percent rise in relative sunlight reduced the influenza index by 1.1 points on a 10-point scale. These results corresponded with the number of flu cases in various counties in New York State.
A 2018 multicenter, randomized, open, controlled clinical trial found that vitamin D may reduce the risk of seasonal influenza A in infants. Researchers looked at 400 infants during the study and broke them into low- and high-dose vitamin D groups.
Out of the 121 total cases, 78 were in the low-dose and 43 were in the high-dose vitamin D group. The symptoms of those infants in the high-dose group also resolved more quickly. The results suggest that a higher dose of vitamin D may help to reduce the risk and improve recovery of the flu during infancy.
Studies on Vitamin D and COVID-19
We have seen a lot of information on social media and certain media outlets about the potential benefits of vitamin D in relation to COVID-19. These are typically based on plenty of research evidence that suggests vitamin D is a key factor in supporting your body during the COVID-19 pandemic.
A 2021 systematic review looked at 49 printed and 5 pre-print publications and a total of 1,403,715 cases on the relationship between vitamin D deficiency, COVId-19 infections, related hospitalization, and mortality. The review found that patients with low vitamin D levels had an increased risk of acute respiratory distress syndrome (ARDS) and mortality from COVID-19.
Another 2021 systematic review and meta-analysis found that vitamin D deficiency may be linked to an increased risk of COVID-19 infection and adequate levels reduced the risk. Analyzing 318 studies on vitamin D and COVID-19 and selecting 14 that met the inclusion criteria, researchers found that people with vitamin D deficiency were 80 percent more likely to get infected with COVID-19.
A 2021 meta-analysis of observational studies looked at 3637 participants to better understand the connection between vitamin D and COVID-19. Similar to other research, they also found that vitamin D deficiency has increased the risk of serious disease and mortality in COVID-19. Patients with low vitamin D levels were more likely to experience cardiovascular disease, hypertension, and other risk factors.
Using Vitamin D supplementation for COVID-19
With the strength of the research evidence, it makes sense to supplement with vitamin D for COVID-19 as a support strategy. Let’s look at some of that evidence.
A 2021 study found that supplementing with vitamin D may help to reduce the length of hospital stay and the risk of mortality in COVID-19. After analyzing the past data of 867 COVID-19 cases, researchers conducted a prospective study with 23 health individuals and 210 cases. 163 of the cases received vitamin D supplementation. The results suggest that vitamin D supplementation has helped to increase the vitamin D levels of patients and raise it above 30 ng/mL only within two weeks.
Some patients had existing comorbidities or health issues that may increase their risk of serious illness, hospitalization, and mortality. Researchers found that patients without comorbidities that didn’t receive vitamin D treatment had a 1.9-fold increased risk of needing to be hospitalized for longer than 8 days compared to patients who had comorbidities but received vitamin D treatment who were more likely to need less than 8 days of hospitalization.
This suggests that adequate vitamin D levels and vitamin D supplementation may be important for those who don’t have any existing health risk factors. Researchers also found that vitamin D supplementation had lowered the mortality rate by 2.14 times in the cases they observed.
Vitamin D and respiratory infections
A population-cohort study found that vitamin D supplementation may improve COVID-19 outcomes. The study looked at COVID-19 cases of individuals who were supplemented with vitamin D between April 2019 and February 2020 and compared them to a control group who did not. Researchers looked at the difference between how they fared during the first wave of the pandemic in 2020.
They found that patients who were supplemented with cholecalciferol had a reduced risk of COVID-19 infection. Those who achieved at least 30 ng/mL 25OHD levels through cholecalciferol supplementation experienced a reduced risk of infection, severe disease, hospitalization, and mortality compared to the control group.
Researchers found that while calcifediol supplementation alone didn’t reduce the risk of COVID-19, those who achieved at least 30 ng/mL 25OHD levels through calcifediol supplementation did have a lower risk of infection, severe disease, hospitalization, and mortality from COVID-19. Researchers found that the key to decreasing the risk of COVID-19 infections and associated severe illness, hospitalization, and mortality may lie in having at least 30 ng/mL 25OHD.
Testing Vitamin D levels
You can test to determine if you are deficient in vitamin D. Testing can help your health care provider determine the best supplementation strategy for you. When it comes to vitamin D levels, most studies use <20 nmol/L for very deficient, <30 nmol/L for deficient and >30 nmol/L for normal vitamin D levels. Optimal levels of vitamin D are over 50 nmol/L and this is what you want to aim for in functional medicine.
You and your functional medicine doctor can look at your 1,25-OH Calcitriol and 25-OH cholecalciferol D3 levels to understand the full picture. Optimal ranges for 1,25 OH Calcitriol are between 50 and 100 ng/ml and for 25-OH vitamin D3 it is also between 50 and 100 ng/ml.
Comprehensive blood analysis
You may also opt for a Comprehensive Blood Analysis (CBA). This test is more sophisticated than most conventional doctors will order. The test will determine your 25(OH) and 1,25(OH). For some individuals, they struggle with vitamin D resistance where they are unable to increase their vitamin D levels in spite of supplementation.
If you fall into this category, your functional medicine doctor can look at an array of markers like parathyroid function, liver markers, calcium and magnesium markers, and more.
For these individuals, we have to look at a wide variety of markers including inflammatory markers, parathyroid function, calcium and magnesium levels, liver markers and more. A CBA will look at inflammatory markers, vitamin A, PTH, calcium, magnesium, complete metabolic panel, complete blood count, liver function markers, blood sugar levels, nutrient deficiencies, and more.
Final thoughts
Vitamin D is an essential vitamin and critical for immune health and fighting respiratory infections. Many Americans are deficient in vitamin D. Raising the awareness of the importance of vitamin D and improving your body’s vitamin D levels is more crucial than ever. You can determine if you are deficient in vitamin D through testing and a Comprehensive Blood Analysis. Then you and your doctor can develop an appropriate supplementation strategy to reach optimal vitamin D levels.