Vitamin D has been in the news quite a bit, recently. It was known for a long time that the “Sunshine Vitamin” is important for our bones, and that if our children didn’t have enough they’d be liable to get rickets. And over the decades, science has continued to discover more about it. But since the coronavirus pandemic arrived there have been rumours and hints that Vitamin D might be an effective weapon in the fight against COVID-19. Urban myth? Fake news? Pie in the sky? Well, no. So, what’s the story?
But first, let’s look at the vitamin itself. Vitamin D is actually a kind of hormone: a substance produced within the body to enable messages to be passed from one part to others, and to switch on and off the functions of various cells. In Vitamin D’s case, it’s produced within the skin by the action of the ultraviolet light in sunlight, and finds its way first to the liver and then to the kidneys. It’s also available to a certain extent through our diet – from some green plants and fungi, and from oily fish. Vitamin D is mainly accessible in two forms, D2 (from plants and fungi: ergocalciferol) and D3 (from fish and sunlight: cholecalciferol), and of these two, D3 is the more effective.
The dietary route is less productive of Vitamin D than is exposure to sunlight. However, as we humans have moved away from our origins in central Africa and into more temperate latitudes, that exposure has been reduced, and with it our ability to produce our Vitamin D physiologically. The sun’s rays are less direct, and there are fewer hours of sunlight the further from the equator we go; plus we wear rather more in the way of clothing – to the extent that without the addition of dietary Vitamin D we would certainly be deficient. To give an example: healthy adults who live in Scotland typically receive considerably less sunlight than those in England’s southern counties and, as a result, without supplementation the level of Vitamin D found in Scots’ blood is typically quite a bit lower by comparison.
Another factor affecting our ability to produce our own Vitamin D is skin colour. Human skin contains melanin, a pigment that is responsible for skin’s darkness. Melanin acts by filtering the amount of ultraviolet light absorbed by the skin; the more melanin, the darker the skin and the less UV is absorbed; and people who naturally and historically live in regions with high levels of sunshine generally have darker skin. But over millennia, as the various strands of early man moved further from the equator, so the amount of melanin in their skin was reduced – they became lighter-skinned – to admit more UV and therefore more Vitamin D, in an attempt to compensate for the lower levels of sunshine. However, in evolutionary terms it’s not that long since man made the move away from the equator, and evolution has not yet caught up, so light-skinned people in temperate latitudes cannot yet make as much physiological Vitamin D as their dark-skinned ancestors who lived near the equator. How this is important will become apparent as you read further.
Essentially, Vitamin D, in concert with another vitamin, K2, controls the way that calcium becomes part of the structure of our bones. With insufficient calcium, bone is soft in youth and brittle in old age. As we’ve seen, the part that Vitamin D plays in making our bones strong has been recognised for many years. So what has changed?
Research during the latter half of the last century hinted that bone health might not be the whole story about the Sunshine Vitamin. It started to become apparent, and further research confirms, that Vitamin D also plays a role in helping us recover from – and in many cases avoid – infection. Vitamin D is part of our immune system.
In fact the body has two sorts of immunity: acquired immunity and innate immunity. Acquired immunity is the sort we’ve known about for quite some time. Special immune cells in our bloodstream – such as T-cells and macrophages, amongst others – attack and attempt to destroy infecting organisms such as bacteria and viruses. They acquire this ability to recognise invaders by being exposed to infection, and the next time that particular organism infects, the immune cells remember them from before and react accordingly. This is the mechanism, too, that lies behind vaccination: rather than put the body through the risk of actually being infected to teach the special cells, vaccines against, for example, flu, polio and covid introduce to the body a safe or modified organism that mimics an invader and teaches the immune system to recognise the real thing. In other words, the mechanism leads to acquired immunity.
Innate immunity, on the other hand, does not need exposure to invaders in order to learn. It’s already part of the system. And this is where recent research on Vitamin D comes in.
Vitamin D’s role in innate immunity works genetically in at least two ways. First, we know that infections can sometimes cause the immune system to overreact, leading to severe inflammation, so that the very processes meant to rid us of illness in fact cause organ damage, often fatally so. This is particularly true of Covid 19, many of the deaths from which have been attributed to so-called “cytokine storms”. One of Vitamin D’s functions is to reduce that process of inflammation significantly before it becomes dangerous. Second, Vitamin D is necessary to stimulate the immune cells to produce a chemical that dissolves an invading organism’s outer shell, thereby destroying it.
So, as well as being instrumental in maintaining our bone health, Vitamin D is also a key part of our immune defences. Without it – in sufficient quantity – our skeleton would be weak and fragile, and our immune system would not work as it should. We would be vulnerable not only to attack from infection but also to the result of the immune system’s overvigorous response. However, our reserves of Vitamin D are soon used up and become depleted, so we need either constant exposure to sunlight, a Vitamin D enriched diet, or supplementation, in order to maintain it at sufficient physiological levels. Of these, supplements are likely to be the most effective, but this is where the problem lies. Although evidence shows that Vitamin D undoubtedly has a role to play in the control of disease, governments – for the time being at any rate – are unwilling to promote its supplementation. More specifically, they are unwilling to agree to increasing the recommended daily amount (the RDA) of Vitamin D.
Why is this? When it was recognised only for its skeletal effect, a specific base level of circulating Vitamin D was recommended, one that was believed would be adequate for maintaining the correct amount of calcium in bones. There was concern that too high a dose could be harmful (there’s a rare condition known as Vitamin D toxicity which leads to hypercalcemia, too much calcium in the blood; and there are other conditions, such as sarcoidosis, in which Vitamin D supplementation might not be advisable). Tests suggested that most people only needed to take a small supplement, and only during the winter months, in order to maintain that base level, and for the US Institute of Medicine (IOM) the amount of that supplement for adults was 15 micrograms (µg) per day – thought to be roughly equivalent to swallowing a daily teaspoonful of cod liver oil. In the UK the National Institute for Health and Care Excellence (NICE) recommended a guideline dose of 400 International Units (IU) a day, which works out at 10 µg/day, somewhat lower than the IOM’s recommendation.
And these recommendations remain in place now, even though science is proving them after all to be inadequate and based on error. Circulating Vitamin D is measured by how much of its metabolite, 25-hydroxyvitamin D – 25(OH)D – is found in the blood. An adult taking a daily dose of 400–600 IU of Vitamin D3 during the winter months might expect to have a level of something like 10 nanograms per millilitre (ng/mL) of 25(OH)D, rather than the 20 ng/mL the IOM set out to achieve. So, hardly enough for bone health; definitely not enough to ensure there’s sufficient Vitamin D to play a part in immunity.
What dosage, then, will ensure sufficient Vitamin D? As in most things, it depends. For example, factors such as obesity can negatively affect Vitamin D’s efficiency. There have been a few clinical research trials to try to establish an RDA, but because Vitamin D supplements are relatively inexpensive there has been little incentive so far for drug companies to fund large scale trials. Without the evidence that would come from such trials, the UK government’s medical advisors are staying with the earlier findings.
Science’s most promising line of research, however, is to look at the evolution of human physiology before human evolutionary development was skewed by early man’s wanderlust. There are people today, living in regions close to where early hominids emerged, whose lifestyle is essentially similar to that of our ancestors. It’s reasonable to assume that, without supplementation, their levels of circulating 25(OH)D are just about what human physiology is finely tuned to work with. And those levels have been found to be somewhere between 40 and 80 ng/mL. To achieve them, an adult living at a temperate latitude would need regular supplementation of Vitamin D during winter months amounting to at least 4000 IU/day.
Is this safe? Is it reasonable? If you’re worried, best check with your GP. Be prepared, though, for mainstream medicine to cleave to the NICE guidelines. However, before his death from brain cancer in 2016, Dr Robert Heaney was one of the world’s foremost experts on Vitamin D. At a symposium on supplementation he was asked to comment on these questions. By way of a reply, he told how at a meeting of Vitamin D research specialists he had passed around the table a slip of paper asking what daily dose each one of them took. All gave an answer, and not one of them took less than 5000 IU/day.
***
The question of dark skin and Vitamin D insufficiency was mentioned above. There have been many reports of how dark-skinned people in countries such as Britain have numbered disproportionately highly in the death rates from Covid 19. Almost always this has been ascribed to disadvantage – poverty, crowded housing, language problems. There’s no doubt that these factors may have a part to play. But what has been overlooked or ignored is that deaths from Covid 19 among dark-skinned people have included many professionals, such as surgeons, accountants, lawyers and architects: people hardly likely to be numbered amongst the disadvantaged. Why is this? As we’ve seen, people with dark skins have a natural barrier to too much of the sun’s UV: melanin. Britain has relatively low levels of sunlight, but nevertheless the melanin in dark people’s skin remains active, blocking out what UV there is, and the consequence is that their skin is able to make very little Vitamin D. Without supplementation, people with dark skins are inevitably deficient, unable to benefit from the natural protection against infection that Vitamin D gives, and so much more vulnerable to Covid 19.
Further reading (not necessary)
Heaney R P, Holick M F: Why the IOM recommendations for vitamin D are deficient (2011)
https://doi.org/10.1002/jbmr.328
Durrant L R, Bucca G, Hesketh A et al.: Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System … (2022)
https://doi.org/10.3389/fimmu.2022.790444
Bob Heaney’s anecdote: Vitamin D, Sunshine, Optimal Health: Putting it all Together. YouTube
https://www.youtube.com/watch?v=B9SNfrE7P1s at 47 mins 19 secs.
Oliver's Twists 
Vitamin D. What’s the story?
But first, let’s look at the vitamin itself. Vitamin D is actually a kind of hormone: a substance produced within the body to enable messages to be passed from one part to others, and to switch on and off the functions of various cells. In Vitamin D’s case, it’s produced within the skin by the action of the ultraviolet light in sunlight, and finds its way first to the liver and then to the kidneys. It’s also available to a certain extent through our diet – from some green plants and fungi, and from oily fish. Vitamin D is mainly accessible in two forms, D2 (from plants and fungi: ergocalciferol) and D3 (from fish and sunlight: cholecalciferol), and of these two, D3 is the more effective.
The dietary route is less productive of Vitamin D than is exposure to sunlight. However, as we humans have moved away from our origins in central Africa and into more temperate latitudes, that exposure has been reduced, and with it our ability to produce our Vitamin D physiologically. The sun’s rays are less direct, and there are fewer hours of sunlight the further from the equator we go; plus we wear rather more in the way of clothing – to the extent that without the addition of dietary Vitamin D we would certainly be deficient. To give an example: healthy adults who live in Scotland typically receive considerably less sunlight than those in England’s southern counties and, as a result, without supplementation the level of Vitamin D found in Scots’ blood is typically quite a bit lower by comparison.
Another factor affecting our ability to produce our own Vitamin D is skin colour. Human skin contains melanin, a pigment that is responsible for skin’s darkness. Melanin acts by filtering the amount of ultraviolet light absorbed by the skin; the more melanin, the darker the skin and the less UV is absorbed; and people who naturally and historically live in regions with high levels of sunshine generally have darker skin. But over millennia, as the various strands of early man moved further from the equator, so the amount of melanin in their skin was reduced – they became lighter-skinned – to admit more UV and therefore more Vitamin D, in an attempt to compensate for the lower levels of sunshine. However, in evolutionary terms it’s not that long since man made the move away from the equator, and evolution has not yet caught up, so light-skinned people in temperate latitudes cannot yet make as much physiological Vitamin D as their dark-skinned ancestors who lived near the equator. How this is important will become apparent as you read further.
Essentially, Vitamin D, in concert with another vitamin, K2, controls the way that calcium becomes part of the structure of our bones. With insufficient calcium, bone is soft in youth and brittle in old age. As we’ve seen, the part that Vitamin D plays in making our bones strong has been recognised for many years. So what has changed?
Research during the latter half of the last century hinted that bone health might not be the whole story about the Sunshine Vitamin. It started to become apparent, and further research confirms, that Vitamin D also plays a role in helping us recover from – and in many cases avoid – infection. Vitamin D is part of our immune system.
In fact the body has two sorts of immunity: acquired immunity and innate immunity. Acquired immunity is the sort we’ve known about for quite some time. Special immune cells in our bloodstream – such as T-cells and macrophages, amongst others – attack and attempt to destroy infecting organisms such as bacteria and viruses. They acquire this ability to recognise invaders by being exposed to infection, and the next time that particular organism infects, the immune cells remember them from before and react accordingly. This is the mechanism, too, that lies behind vaccination: rather than put the body through the risk of actually being infected to teach the special cells, vaccines against, for example, flu, polio and covid introduce to the body a safe or modified organism that mimics an invader and teaches the immune system to recognise the real thing. In other words, the mechanism leads to acquired immunity.
Innate immunity, on the other hand, does not need exposure to invaders in order to learn. It’s already part of the system. And this is where recent research on Vitamin D comes in.
Vitamin D’s role in innate immunity works genetically in at least two ways. First, we know that infections can sometimes cause the immune system to overreact, leading to severe inflammation, so that the very processes meant to rid us of illness in fact cause organ damage, often fatally so. This is particularly true of Covid 19, many of the deaths from which have been attributed to so-called “cytokine storms”. One of Vitamin D’s functions is to reduce that process of inflammation significantly before it becomes dangerous. Second, Vitamin D is necessary to stimulate the immune cells to produce a chemical that dissolves an invading organism’s outer shell, thereby destroying it.
So, as well as being instrumental in maintaining our bone health, Vitamin D is also a key part of our immune defences. Without it – in sufficient quantity – our skeleton would be weak and fragile, and our immune system would not work as it should. We would be vulnerable not only to attack from infection but also to the result of the immune system’s overvigorous response. However, our reserves of Vitamin D are soon used up and become depleted, so we need either constant exposure to sunlight, a Vitamin D enriched diet, or supplementation, in order to maintain it at sufficient physiological levels. Of these, supplements are likely to be the most effective, but this is where the problem lies. Although evidence shows that Vitamin D undoubtedly has a role to play in the control of disease, governments – for the time being at any rate – are unwilling to promote its supplementation. More specifically, they are unwilling to agree to increasing the recommended daily amount (the RDA) of Vitamin D.
Why is this? When it was recognised only for its skeletal effect, a specific base level of circulating Vitamin D was recommended, one that was believed would be adequate for maintaining the correct amount of calcium in bones. There was concern that too high a dose could be harmful (there’s a rare condition known as Vitamin D toxicity which leads to hypercalcemia, too much calcium in the blood; and there are other conditions, such as sarcoidosis, in which Vitamin D supplementation might not be advisable). Tests suggested that most people only needed to take a small supplement, and only during the winter months, in order to maintain that base level, and for the US Institute of Medicine (IOM) the amount of that supplement for adults was 15 micrograms (µg) per day – thought to be roughly equivalent to swallowing a daily teaspoonful of cod liver oil. In the UK the National Institute for Health and Care Excellence (NICE) recommended a guideline dose of 400 International Units (IU) a day, which works out at 10 µg/day, somewhat lower than the IOM’s recommendation.
And these recommendations remain in place now, even though science is proving them after all to be inadequate and based on error. Circulating Vitamin D is measured by how much of its metabolite, 25-hydroxyvitamin D – 25(OH)D – is found in the blood. An adult taking a daily dose of 400–600 IU of Vitamin D3 during the winter months might expect to have a level of something like 10 nanograms per millilitre (ng/mL) of 25(OH)D, rather than the 20 ng/mL the IOM set out to achieve. So, hardly enough for bone health; definitely not enough to ensure there’s sufficient Vitamin D to play a part in immunity.
What dosage, then, will ensure sufficient Vitamin D? As in most things, it depends. For example, factors such as obesity can negatively affect Vitamin D’s efficiency. There have been a few clinical research trials to try to establish an RDA, but because Vitamin D supplements are relatively inexpensive there has been little incentive so far for drug companies to fund large scale trials. Without the evidence that would come from such trials, the UK government’s medical advisors are staying with the earlier findings.
Science’s most promising line of research, however, is to look at the evolution of human physiology before human evolutionary development was skewed by early man’s wanderlust. There are people today, living in regions close to where early hominids emerged, whose lifestyle is essentially similar to that of our ancestors. It’s reasonable to assume that, without supplementation, their levels of circulating 25(OH)D are just about what human physiology is finely tuned to work with. And those levels have been found to be somewhere between 40 and 80 ng/mL. To achieve them, an adult living at a temperate latitude would need regular supplementation of Vitamin D during winter months amounting to at least 4000 IU/day.
Is this safe? Is it reasonable? If you’re worried, best check with your GP. Be prepared, though, for mainstream medicine to cleave to the NICE guidelines. However, before his death from brain cancer in 2016, Dr Robert Heaney was one of the world’s foremost experts on Vitamin D. At a symposium on supplementation he was asked to comment on these questions. By way of a reply, he told how at a meeting of Vitamin D research specialists he had passed around the table a slip of paper asking what daily dose each one of them took. All gave an answer, and not one of them took less than 5000 IU/day.
***
The question of dark skin and Vitamin D insufficiency was mentioned above. There have been many reports of how dark-skinned people in countries such as Britain have numbered disproportionately highly in the death rates from Covid 19. Almost always this has been ascribed to disadvantage – poverty, crowded housing, language problems. There’s no doubt that these factors may have a part to play. But what has been overlooked or ignored is that deaths from Covid 19 among dark-skinned people have included many professionals, such as surgeons, accountants, lawyers and architects: people hardly likely to be numbered amongst the disadvantaged. Why is this? As we’ve seen, people with dark skins have a natural barrier to too much of the sun’s UV: melanin. Britain has relatively low levels of sunlight, but nevertheless the melanin in dark people’s skin remains active, blocking out what UV there is, and the consequence is that their skin is able to make very little Vitamin D. Without supplementation, people with dark skins are inevitably deficient, unable to benefit from the natural protection against infection that Vitamin D gives, and so much more vulnerable to Covid 19.
Further reading (not necessary)
Heaney R P, Holick M F: Why the IOM recommendations for vitamin D are deficient (2011)
https://doi.org/10.1002/jbmr.328
Durrant L R, Bucca G, Hesketh A et al.: Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System … (2022)
https://doi.org/10.3389/fimmu.2022.790444
Bob Heaney’s anecdote: Vitamin D, Sunshine, Optimal Health: Putting it all Together. YouTube
https://www.youtube.com/watch?v=B9SNfrE7P1s at 47 mins 19 secs.