Topic Review: Vitamin D

1922 The discovery of a ‘new vitamin’ that cured the bone disease known as ‘rickets’ caused by Vitamin D deficiency

50% estimated percentage of people today with Vitamin D deficiency

$1,100,000,000 Global market for Vitamin D supplements

600 International units recommended for Vitamin D for ages 1-70 years old

800 International units recommended for Vitamin D for ages over 70 years old

170 the percentage daily intake of Vitamin D from one tablespoon of cod liver oil

71 the percentage daily intake of Vitamin D from 85gram serving of salmon

46 the percentage daily intake of Vitamin D from half-cup of mushrooms

 

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ORIGIN STORY

Curing the ‘English Disease’ with cod liver oil and sun

Rickets was one of the most debilitating diseases of childhood throughout the early 20th century. It caused serious skeletal deformities of the spine and stunted growth. Some 60-80% of children in poor households had rickets and it was getting more prevalent during the industrial revolution throughout Great Britain – with some calling it the ‘English Disease’.

In 1890, doctor Theodore Palm was curious to find that rickets was not as prevalent in lower latitude countries in East Asia. So Palm theorised that rickets was related to the amount of sunlight people received – which would be proved correct.

Meanwhile Sir Edward Mellanby, experimented with puppies, feeding them an oats-diet indoors. He found they developed rickets identical to the human version but giving the dogs cod liver oil cured them – and assumed it was because of Vitamin A.

In the USA, biochemist Elmer McCollum went a step further from Sir Mellanby’s experiment, feeding sick animals with cod liver oil that had Vitamin A removed. The oil also healed the sick dogs, so McCollum concluded it contained an unknown new vitamin – he called it vitamin D (the next available on the alphabet).

A generation of mothers in northern latitudes forced their kids to have daily cod liver oil. Along with the knowledge that sunlight also helped – rickets was largely cured.

The industrial revolution took large numbers of people from the land into factories – cutting off their sunlight. Thick pollution also lowered the amount of ultraviolet light reaching cities. There’s only a few foods that contain good amounts of Vitamin D (fatty fish like salmon or mackeral are good) – the vast majority of Vitamin D is manufactured when UV light hits our skin.

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THE CONSENSUS

Is Vitamin D important for bone health?

100% Likely via 4 experts

Read the full answers to this question here. Experts say that Vitamin D is important to build and maintain healthy bones. That’s because calcium, the primary component of bones, can only be absorbed by your body from food when vitamin D is present. “Its primary role is to maintain the levels of calcium within our bodies at optimal levels” says Dr Bill Ribbans, an orthopedic expert from the University of Northampton. “It does this by helping the calcium in our diet enter our blood stream and reduces the amount of calcium that otherwise be lost in our urine.”

When you have vitamin D deficiency, you do not have enough calcium in your body. Then the body tries to compensate by taking calcium out of your bone, causing your bone to become more fragile. Aside from causing rickets in children, experts say a Vitamin D deficiency causes the adult equivalent disease called osteomalacia. “Additionally, both clinical and experimental studies suggest low vitamin D levels can be associated with osteoporosis although the links are not straightforward”, says Dr Bill Ribbans.

What about the claim made that Vitamin D helps reduce bone fractures? That is uncertain

Dr Xingzhong Xin, an expert from UNSW Sydney says “Vitamin D is important for optimal musculoskeletal health because it allows your body to absorb calcium, which promotes mineralisation in bone, and maintains muscle function. Strong bone and good muscle function help protect against falls and bone fractures.

While higher vitamin D levels in the blood is associated with lower risk of bone fractures, evidence shows that taking daily standard vitamin D supplementation alone is not enough to reduce fracture risk. Instead, supplementing vitamin D in combination with calcium is a more promising strategy to prevent bone fracture.”

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THE CONSENSUS

Does a vitamin D deficiency elevate the risk of multiple sclerosis?

100% Likely via 9 experts

Read the full answers to this question here. Multiple sclerosis is a devastating illness with high mortality rates. Is Vitamin D a risk factor? The expert consensus is unanimous in agreeing that a vitamin D deficiency seems to make us more vulnerable to MS.

Low vitamin D is a risk factor, but supplementation doesn’t work for MS

“There are now many studies that show that a low level of vitamin D (or really 25-hydroxyvitamin D since that is what we use to measure vitamin D status) in the blood is associated with an increased risk of MS” writes Professor Robyn Lucas, epidemiologist and Vitamin D expert from Australian National University.

Other experts agree. “The evidence for low vitamin D as a predictor of MS risk is strong” writes Dr Dimitry Krementsov, an MS expert from the University of Vermont. Others, like Professor Prue Hart from the University of Western Australia notes that while a Vitamin D deficiency is a risk factor, there’s no causal role for vitamin D in multiple sclerosis.

And trials using vitamin D supplements for MS patients have been disappointing Prof Hart says. Although Dr Krementsov says more recent Mendelian randomization studies lend support to it having a causative role but “Unfortunately, as mentioned [by Prof Hart[, clinical trials have not shown a consistent benefit to supplementation (e.g. this recent metanalysis). Dr Krementsov also points out that genetics are important, as white populations are more susceptible.

The Sun seems more effective for MS than supplements

Professor Lucas writes in detail that her work with colleagues shows that having “higher sun exposure over the lifecourse reduces the risk of MS (but this could just be a vitamin D effect)”. And there might be wider benefits from the sun on our immunology writes Professor Joost Smolders, a leading MS expert from the Netherlands Institute for Neuroscience who explains how sunlight “is the most important source of vitamin D which has immune-suppressive effects by itself.”

There’s no denying that low vitamin D levels seem to be a genuine risk factor for multiple sclerosis but many questions remain about the causal relationship and whether increasing vitamin D intake can help prevent MS. Also, it appears unanimous the vitamin D supplementation is entirely ineffective in raising levels. Whereas exposure to the sun throughout the lifespan might act as a legitimate preventative measure.

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THE CONSENSUS

How much sun do you need for Vitamin D? Is 5-minutes enough?

100% Negative via 7 experts

Read the full answers to this question here. Exposure to UV rays helps us produce vitamin D while also important for our mental health. But too much time in the sun can lead to severe sunburns, sunstroke, and – over time – skin cancer. Some say spending just 5-minutes is enough at least for Vitamin D production. Is that true? We asked 7 experts who all said no. They say that the amount of sun needed to produce adequate levels of Vitamin D varies alot, depending on your latitude, time of year and your skin type. Here’s what we learned.

5minutes is not enough sun

Even if you are nude, 5 mins. of summer sun at noon for skin types II-III (mostly whitish skin) is inadequate to produce enough vitamin D” says skin cancer and Vitamin D expert Dr Dianne Godar. “You would need a whole body exposure of at least 5 mins. per side to get close to making enough vitamin D for good health (but depends on latitude and altitude as well).”

Professor Ann Web is an expert in UV radiation and Vitamin D production from the University of Manchester. She writes a detailed answer explaining that in recent research in the UK, people living above 50deg latitude need about 9-minutes of lunchtime sun during between March to September to provide for vitamin D needs. All they would need is to wear shorts/skirt and t-shirt, exposing 35% of their skin. This would also likely be safe from sunburn she says. For people with skin type V (brown, South Asian) the equivalent exposure time in the UK is 25 minutes per day.

However during October – February in the UK there is insufficient UV radiation in sunlight to initiate any appreciable vitamin D synthesis she says. That is where diet and/or supplements might help (see below).

It’s also important to know that UV gets blocked by glass – so you can’t burn or get Vitamin D from behind glass in a car or office window – it needs to be full sunlight with UV. Also, age is a big factor too. “you make about half as much Vitamin D from the same amount of sun at age 70 as you made when you were age 20” says Dr Godar.

What about overusing sunscreen? Is that a problem for Vitamin D?

“No” says Dr Reinhold Vieth, Vitamin D expert from the University of Toronto, “BUT with a minor technicality.”

Sunscreen does block vitamin D production but in practice he says, people use sunscreen so that they can stay out in the sun longer. In population surveys, people who use sunscreens do not have lower levels of vitamin D nutrition (serum 25-hydroxyvitamin D) compared to those who do not use them. Even if they do use a potent sunscreen, people eventually do develop a tan. A tan is a sign that vitamin D is also produced says Dr Vieth.

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THE CONSENSUS

Does vitamin D protect against COVID-19?

80% Uncertain via 5 experts

Read the full answers to this question here. Many headlines have suggested vitamin D deficiency could increase the risk of dying from COVID-19, and in turn, that we should consider taking vitamin D supplements to protect ourselves. Is this all just hype, or could vitamin D really help in the fight against COVID-19?

Although some evidence suggests a Vitamin D deficiency may make you more susceptible to infection, the consensus is uncertain whether Vitamin D helps or protects against COVID.

In terms of general immune health, adequate amounts of Vitamin D is important according to Dr. Anthony Fauci, the US governments top immunologist: “If you are deficient in Vitamin-D, that does have an impact on your susceptibility to infection” he recently said on Instagram.

So how does Vitamin D potentially help our immunity? Professor Elina Hyppönen, nutritional epidemiologist from the University of South Australia tells us how.

Vitamin D, the immune system and respiratory infections

At least in theory, there may be something to the claims that Vitamin D helps protect against COVID. Nearly all immune cells have vitamin D receptors, showing vitamin D interacts with the immune system. The active vitamin D hormone, calcitriol, helps regulate both the innate and adaptive immune systems, our first and second lines of defence against pathogens.

And vitamin D deficiency is associated with immune dysregulation, a breakdown or change in the control of immune system processes. Many of the ways calcitriol affects the immune system are directly relevant to our ability to defend against viruses. For example, calcitriol triggers the production of cathelicidin and other defensins – natural antivirals capable of preventing the virus from replicating and entering a cell.

Calcitriol can also increase the number of a particular type of immune cell (CD8+ T cells), which play a critical role in clearing acute viral infections (such as influenza) in the lungs. Calcitriol also suppresses pro-inflammatory cytokines, molecules secreted from immune cells which, as their name suggests, promote inflammation. Some scientists have suggested vitamin D might help to alleviate the “cytokine storm” described in the most severe COVID-19 cases.

Evidence from randomised controlled trials suggests regular vitamin D supplementation may help protect against acute respiratory infections. A recent meta-analysis brought together results from 25 trials with more than 10,000 participants who were randomised to receive vitamin D or a placebo.

It found vitamin D supplementation reduced the risk of acute respiratory infections, but only when it was given daily or weekly, rather than in a large single dose. The benefits of regular supplementation were greatest among participants who were severely vitamin D deficient to begin with, for whom the risk of respiratory infection went down by 70%. In others the risk decreased by 25%.

Vitamin D and COVID-19

“There is currently no evidence that vitamin D protects against COVID-19, either in terms of initial infection or severity of disease once infected” writes Dr Claire Hastie from the University of Glasgow.

Most studies have linked vitamin D levels to COVID infections on population data – and there are some interesting links being made writes Dr Karin Amrein, a Vitamin D expert from Austria. The first appearance of COVID came from winter months in the Northern Hemisphere, while “the higher incidence in non-white populations and worse outcomes would suggest a role of vitamin D.”

“There are very good data that vitamin D reduces acute respiratory infections (https://www.bmj.com/content/356/bmj.i6583) and asthma exacerbations” Dr Amrein says and “Recent US data from a large dataset clearly showed a higher rate of COVID-19 positivity in vitamin D deficient individuals.”

Dr Claire Hastie from the University of Glasgow disagrees any link can be drawn about Vitamin D writing “Studies that suggest a link have either failed to take confounding variables into account… or they measured 25(OH)D once patients are already ill. This introduces the possibility of reverse causation, i.e. COVID-19 leading to lower vitamin D rather than low vitamin D leading to COVID-19, because vitamin D is a negative acute phase reactant. All existing evidence is limited due to its observational nature. For a definitive answer on whether there is a link we await the results of randomised controlled trials (RCTs), of which there are several underway.”

Although there is no evidence that Vitamin D protects against COVID-19, other experts like Dr Reinhold Vieth from the University of Toronto say that taking Vitamin D supplements is a low risk strategy but “Certainty on the topic will probably only come in a year or two, after it is too late to make any difference to people.”

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During the wintertime at latitudes above 35deg, there is negligible production of vitamin D in the skin. In addition, vitamin D can be found in a very limited variety of diets, including fatty fish, cod liver oil and mushroom. Although it is fortified in some products of milk and orange juice, you need to ingest at least six to eight servings a day to achieve its minimal daily requirement. Thus, you are likely to have vitamin D deficiency at some point unless you live in a tropical area and have regular sunlight exposure, and therefore vitamin D supplement is necessary to achieve healthy vitamin D status which is essential for bone health.

There is promising evidence that connects a healthy level of vitamin D with decreased risks of several other non-skeletal chronic diseases such as diabetes mellitus, cardiovascular disease, cancers and autoimmune diseases. However, it is still debatable if vitamin D supplementation has a significant benefit to prevent these non-skeletal diseases, or vitamin D only serves a marker of good general health.

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TAKEAWAYS

• Vitamin D is important for our bone health, linked to our mental health and a risk factor for Multiple Sclerosis
• There is emerging evidence it helps protect against certain infections and helps our immunity
• It is still uncertain whether Vitamin D helps protect against disease like COVID-19, cancer and cardiovascular disease
• The best source of Vitamin D is from the sun (in moderation). In the UK for example, during summer (or similar latitudes) ~9 minutes in midday sun wearing shorts/shirt is likely enough
• Most of us however will have a Vitamin D deficiency during winter months – so you can help avoid deficiency by eating fatty fish (salmon or trout). Mushrooms are also rich in Vitamin D
• You can also take supplements but consult your doctor first to get the right advice for you