I was at a physical and asked my doctor if vitamin D could be added to my labs.
“There’s no evidence it’s helpful,” the doctor said.
I wasn’t up for debate and simply told her I take vitamin D and like to know my levels. In fact, every year I like to check to see how if the amount I’m taking is enough to keep my levels above 30ng/ml (nanograms per milliliter). She reluctantly agreed.
I never went back to see this doctor and I still get my vitamin D levels checked. When hearing about the link between Covid-19 and vitamin D, I was intrigued.
Everything I’ve ever read taught me that vitamin D plays a key role in the immune system. And the groups deemed higher risk for complications of Covid-19 including people with darker skin and the elderly, are also the same groups more likely to have lower vitamin D levels.
So, I took some time to dig into the research and wanted to share what I found.
First signs of a link between COVID-19 and Vitamin D
Well into the coronavirus pandemic health experts because to notice patterns. First, is the difference between mortality rates in different counties.
When mortality per million is plotted against latitude, countries above 35 degrees north have a higher mortality rate. This is the point where people do not receive sufficient sunlight to make vitamin D during winter.
Researchers from Trinity College Dublin, Ireland reviewed the evidence on current vitamin D status, countries in these high-risk climates, and mortality from COVID-19.
The two hardest-hit countries, Italy and Spain, have lower vitamin D levels compared to Norway, Sweden, and Finland, which have fared much better. Experts speculate this is due to strong fortification and supplementation programs in these countries.
There are also data showing that BAME (black, Asian, and Minority Ethnic), people with a BMI >30, the elderly (especially home-care residents), and individuals with underlying health conditions, have higher severity and mortality from Covid-19.
All of these groups are at increased risk of vitamin D deficiency.
Researchers from Northwestern University examined the relationship between COVID-19 and vitamin D. They took data across countries with a large number of cases including China, Germany, South Korea, Germany, Italy, France, Spain, Iran, Switzerland, the UK, and the US.
Combining this data with established work relating to vitamin D and CRP levels, they discovered a link between vitamin D deficiency and Covid-19 disease severity.
“Our analysis shows that it might be as high as cutting the mortality rate in half,” said lead researcher Vadim Backman in a press release about the study. “It will not prevent a patient from contracting the virus, but it may reduce complications and prevent death in those who are infected.”
It’s important to note that these results were published in MedRxiv, which is designed for sharing preliminary data and is not peer-reviewed.
Blood levels of vitamin D are expressed in either ng/ml (nanogram per milliliter) or nmol/l (nanomoles per liter). To convert ng/ml to nmol/l multiply by 2.5. And to convert nmol/l to ng/ml divide by 2.5. For example 75nmol/l = 30ng/ml.
Vitamin D levels of COVID-19 patients
In another study published on MedRxiv led by Dr. Frank H. Lau, MD, FACS; Department of Surgery, Louisiana State University, data were collected from 20 COVID-19 patients who had vitamin D levels checked during hospital visits.
Vitamin D insufficiency (<30ng/ml) in ICU patients was 84.6% and 54.1% in floor patients. Of those under 75 years of age in the ICU, most had vitamin D levels below 20ng/ml.
Dr. Mark Alipio from Davao Doctors College; University of Southeastern Philippines gathered vitamin D data on 212 COVID-19 hospitalized patients. Although most patients had vitamin D levels <30ng/ml, most were not severely deficient. For every standard deviation increase in vitamin D, patients were 8 times more likely to have mild versus severe outcomes and 20 times more likely to have mild versus critical outcomes.
Of course, it’s difficult to tell if a low vitamin D caused the critical illness or the other way around.
A study in Diabetes & Metabolic Syndrome didn’t find a link between the risk of getting COVID-19 and vitamin D levels in the UK. But when separated out by race, whites had a median vitamin D level of 13.52ng/ml, blacks had 8.4ng/ml, and south Asians 5.7ng/ml. According to a report from the Institute of Fiscal Studies, blacks and Asians are dying at higher rates than whites in the UK.
Vitamin D will not prevent a patient from contracting the virus, but it may reduce complications and prevent death in those who are infected.” — Vadim Backman
Why vitamin D?
Although vitamin D plays a key role in bone health, it also is essential for the immune system. Vitamin D enhances immunity by helping reduce the pro-inflammatory TH1 cytokines. This may help to prevent the “cytokine storm” we’ve been hearing so much with the novel coronavirus.
“Cytokine storm can severely damage lungs and lead to acute respiratory distress syndrome and death in patients,” said Northwestern University study author Ali Daneshkhah, in a press release. “This is what seems to kill a majority of Covid-19 patients, not the destruction of the lungs by the virus itself. It is the complications from the misdirected fire from the immune system.”
There’s also an established link between low vitamin D levels and acute respiratory tract infections. In one review in BMJ, researchers examined 25 randomized control studies. Vitamin D supplementation reduced the risk of acute respiratory tract infections in all people. The effect was greatest in those who were the most vitamin D deficient (<10ng/dl) getting weekly or daily vitamin D instead of large doses.
Vitamin D has been shown to have anti-thrombotic functions and could help with COVID-19-associated coagulopathy (CAC). This is the tendency for the blood to clot due to infection which is a regular occurrence in severe Covid-19 cases.
Vitamin D has also been identified as a potential “therapeutic to mitigate the pandemic” along with Quercetin and estrogen with clinical trials underway. This has to do with vitamin D interfering with Covid-19 functions by altering how certain genes are expressed.
What about children?
It’s important to note that children are not a high-risk group of Covid-19. According to one large study in Pediatrics, 90% of children who tested positive of COVID-19 had none, mild or moderate symptoms.
Although there are a variety of theories as to why this is the case, one is that children more heavily rely on their innate immune system, the body’s first line of defense.
With time and aging, this response can become delayed. Vitamin D may help adults have a more effective innate response but also help to calm down the longer-term adaptive immune response.
Vitamin D levels are also lower in the winter months and thought to play a role in the seasonality of the flu and acute respiratory diseases. For example, in north and central regions in the US, mean vitamin D levels in the winter are 21ng/ml. This increases to 28ng/ml in the summer. In southern regions, mean levels are 24ng/ml and increase to 28ng/ml in the summer.
How much Vitamin D do people need?
I was talking to a friend about vitamin D and she asked how much is recommended. This is where things turn complicated. Recommendations from the Institute of Medicine (IOM) are 600IU after the age of one –and 800U after 70.
Yet this recommended amount is for bone health with target vitamin D blood levels >20ng/ml. In 2011 when IOM developed these guidelines, they said there was not enough evidence to recommend vitamin D to help prevent or treat other health conditions.
There’s an abundant amount of observational evidence linking lower vitamin D with many health conditions from heart disease to diabetes to autoimmune disease. But the scope of this article is vitamin D’s role in the immune system with a focus on Covid-19.
Some experts believe higher blood levels of vitamin D are needed to keep the immune system working well. The Endocrine Society recommends >30ng/ml of vitamin D. And studies to date on immune health support these higher levels as well.
But if you stick with the IOM recommendations, most will not get to 30ng/ml. According to the Endocrine Society, it takes 1500-2000IU to reach 30ng/ml. And if someone has much lower levels, say <12ng/ml, they will need even higher amounts to bring their levels up with the support of a doctor.
Most Americans – about 80% — have vitamin D levels above 20ng/ml according to the recent 2011-2014 NHANES data. But when separated by race less than 50% of blacks did, 63% of Asians, 68% of Hispanics, and 86% white.
But most still do not get above 30ng/ml. According to 2009-2010 NHANES, 64% have levels <30mg/ml.
Vitamin D sources
The average vitamin D intake from food is about 200IU. 1 cup of milk has 100IU and other fortified foods have similar amounts. Fatty fish like salmon has more but most people don’t eat fish every day. (see graph)
The sun has been the primary source of vitamin D for millions of years. When the skin is exposed to UVB light it makes vitamin D and can store as much as 20,000IU in the body.
Yet those farther away from the equator don’t get sufficient levels during winter. And someone with darker skin will need 3-10 times more the sun than someone with fair skin.
No to mention, we are all being asked to stay out of the sun or use sunscreen to prevent skin cancer. And sunscreen blocks UVB rays. For instance, SPF 30 blocks 97% of UVB rays.
Not everyone agrees that we need to stay out of the sun. Vitamin D expert Michael Hollick recommends sensible sun exposure. He suggests applying sunscreen to the face and chest while allowing sun exposure to the arms and legs three times a week for about 10 minutes or before burning would occur.
The chart below estimates how much sun exposure it takes to get 1000IU vitamin D. Skin type matters as those with darker skin need more time in the sun than those with fair skin.
You can get an app to measure the Ultraviolet Index (UVI) where you are. Lower numbers (1 to 2) mean you don’t get much UV rays but as numbers go up so does your exposure.
But for most people, vitamin D supplements are needed to help fill in the gaps between diet and the sun.
Picking a Vitamin D side
At the end of March – when COVID-19 took off on the US — a group of three doctors wrote a thoughtful paper encouraging health professionals to collect data on vitamin D and treat deficiency early.
They mentioned the established link between vitamin D and respiratory illnesses and argued for the potential role it could play in COVID-19. The feedback they got was polarizing with some attacking them for relying on “observational evidence.”
It’s like my experience with the doctor all over again.
It seems there is the camp of health professionals who believe in vitamin D and the camp that disregards it.
Much of the controversy about vitamin D has to do with the disappointing randomized control trials (RCTs). Yet there are challenges and design flaws with RCTs which is beyond the scope of this post.
Although more research is needed, right now everyone is looking for ways to fight COVID-19. And vitamin D has the potential to be a cost-effective, viable option.
Vitamin D isn’t just any vitamin
I’ve always been taken vitamin D’s story. First, is the fact that it acts more like a hormone in the body than a vitamin. The body’s exposure to UVB light has historically been the primary source. Low intake is not due to poor diets like with other vitamins.
Modern-day hunter-gatherers living in Tanzania have mean vitamin D levels of 46ng/ml. This is with type 6 skin, moderate clothing, and a majority of the time spent outdoors.
But that’s the exception as now most people spend their days in an office, use sunscreen, and live in polluted areas. These are all factors that can hinder the amount of UVB light that reaches the skin.
We also have a substantial period of history when rickets due to vitamin D deficiency claimed many young lives (read about it here). This happened as people began to live in more urban environments.
It took nearly three centuries to discover the cause (vitamin D deficiency) and a cure (sunlight and cod liver oil)!
And the discovery of vitamin D was only 100 years ago. We still have so much to learn about how it affects the human body.
More benefit than cost
There doesn’t seem many downsides to keeping my family’s vitamin D levels up. And there’s a lot of potential upsides.
That’s because vitamin D supplements are considered safe. The 2000IU used in a recent trial showed no signs of toxicity over 5 years. According to the IOM and Endocrine Society, vitamin D toxicity is rare and diagnosed at levels >150ng/ml.
Still, taking more than the upper limit (4000IU) should include monitoring by a doctor to look for signs like hypercalcemia but most importantly, to check vitamin D blood levels. Of course, this is for adults. See this post for more on children and vitamin D.
There’s little doubt that vitamin D is a complicated and controversial subject. Hopefully, in time, we’ll have better answers for the role vitamin D plays in COVID-19 duration and severity, and other respiratory illnesses that claim lives.
But in the meantime, supplementing with vitamin D can be a smart move. And some of us may even decide to get sensible sun exposure this summer.
More importantly, maybe this pandemic is the push health professionals need to get some agreement on vitamin D. According to one review, US physicians are all over the place in how they handle vitamin D screening. Most said they’d welcome clear-cut guidelines and procedures regarding testing and supplementation.
And if insurance only covers high-risk groups, that’s okay too. There are labs in the US that will do a vitamin D test for as little as $48.00 but I’m not sure how that works in other countries.
History tells us that humans living in modern times will always need to be conscious of their vitamin D status. Unfortunately, history also tells us it takes very difficult circumstances to be reminded of that.
And we just happen to be living through one of those times right now.