The existence of Vitamin D was established in the 17th century because two men, Dr. Daniel Whistler (1645) and Professor Francis Glisson (1650), recognised that rickets was a deficiency disease. Only much later, in the early 20th century was science developed enough to identify what Vitamin D is and how it functions.

Although this vitamin was discovered a long time ago, it has been something of a stepchild in the nutrition world. This is probably because it has been assumed that everyone gets enough of it anyway.

After all, exposure to sunlight is all that is needed for the body to generate its own supplies. And this capacity means that it is technically not a vitamin at all, but rather a hormone! Now, however, we are realising anew just how important Vitamin D is for our health.

What it does

Vitamin D controls the expression of more than 200 genes. In this way it plays a role in many metabolic functions including calcium metabolism, neurotransmitters such as serotonin, the immune system and cell growth and death (called apoptosis).

In fact, recent studies have found that more than one million people die every year from lack of sun exposure and subsequent vitamin D deficiency!

Production in the skin

Vitamin D is actually a group of fat-soluble steroid compounds. The two major forms are vitamin D2 (ergocalciferol), which is produced by plants, invertebrates, fungi and invertebrates, and vitamin D3 (cholecalciferol), which is produced by humans and other vertebrates.

Vitamin D3 is produced in skin exposed to sunlight, specifically UVB radiation (photochemically) from 7-dehydrocholesterol which is already present in that organ.

Thereafter it undergoes further modification in the liver and kidneys and other organs (so having liver or kidney disease predisposes individuals to Vitamin D deficiency).

The two most important factors that govern the generation of Vitamin D3 in the skin are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol in the deeper layers of the epidermis.

Other factors influencing Vitamin D production in the skin


Vitamin D3 production in the skin is affected by the presence and concentration of melanin which functions as a light filter in the skin.

As a result, the concentration of melanin in the skin is related to the ability of UVB light to penetrate the skin and cause the photo-conversion of Vitamin D3 from its precursor.

So people with higher skin melanin content (dark-skinned people) will simply require more time in sunlight to produce the same amount of vitamin D as individuals with lower melanin content (light-skinned people).

In white skin, about 20 minutes of UV-B exposure of a significant skin area is often enough for Vitamin D3 production whereas it can take up to twenty times longer for darkly pigmented skin.

The sun's rays:

Another factor determining the production of Vitamin D3 in the skin is the person’s distance from the equator. The season of the year, and the amount of time spent in the sun.

So, where you live plays an important role. At latitudes north and south of 35 degrees, UV-B irradiation is very low for long periods of the year – winter, autumn (fall) and the spring.

So for at least 6 months Vitamin D3 production will be inadequate, even is you spend a significant amounts of time outdoors. Added to this is the fact that very little skin is exposed during these colder months. (The UV Advantage, Dr. Michael Holick)

Indoor lifestyles:

For many people most of their daylight hours are spent indoors because of work requirements and other lifestyle choices.

This means that their skin is exposed to too little direct sunlight on a regular basis to produce adequate supplies of Vitamin D3 –such people are almost certainly deficient in this vitamin.

In addition, glass filters out the UV-B rays, so travelling in your car and feeling the sun on you arms does not mean that your skin is making Vitamin D3!

The recommended exposure is at least 15 to 20 minutes in the sunlight three to five days per week and as much of your skin should be exposed as possible!


Then we are also afraid of the sun’s effects! We have been persuaded that we should not go out into the sun without slathering sunscreen all over our exposed skin. What we have failed to recognise is that a sunscreen of SPF 8 reduces vitamin D production by 95%!

The reason for using sunscreen is to protect ourselves against the damaging effects of the sun which can ultimately lead to cancer. The rays that are most dangerous are the UV-A rays while the sunscreens are most effective at screening out UV-B rays.

So the small advantage that is gained is totally offset by the disadvantage of developing Vitamin D3 deficiency!

Even if you find a suitable sunscreen which filters out UV-A rays (and does not contain toxic ingredients) it is recommended that it only be used when you are planning to stay out of doors for a long time, and have no way of covering up the exposed skin.

It is far better to go into the sun with no sunscreen for long enough to get your Vitamin D3 (when your skin has turned very slightly pink, as a white person) and then cover your exposed skin with a hat and some loose clothing.

So why is Vitamin D so important?

Vitamin D plays an important role in the health of many organs.

Blood calcium levels

Vitamin D plays a crucial role by regulating the calcium and phosphorus levels in the blood.

This is done either by increasing absorption from the intestines, or, if dietary calcium is inadequate, by stimulating the release of calcium from the bones (or the teeth). On the other hand, if the calcium levels rise too high, excretion by the kidneys is increased.

Healthy bones

The classic Vitamin D deficiency disease is rickets, which is a malformation in the long bones of the legs in developing children. The adult equivalent is osteomalacia which results in weak muscles and bones.

As with many deficiencies, the early stages of the problem may be symptom-free and so go undetected in the initial stages.

Vitamin D plays a role in maintaining healthy bones because it is essential for proper absorption of calcium from the intestines and reabsorption from the kidneys, and also controls the levels of calcium (and phosphate) in the blood.

Bone is constantly undergoing growth and remodelling (by cells called osteoblasts and osteoclasts). This process depends upon Vitamin D. If there is a deficiency bones become thin, brittle and even misshapen

Osteoporosis is strongly associated with low vitamin D – largely because too little calcium is absorbed when Vitamin D is lacking. In fact, osteoporosis is a chronic disease caused by a long-term deficiency of calcium and vitamin D.

Postmenopausal women with osteoporosis respond rapidly and positively to higher levels of D together with calcium and magnesium.

Back pain and other musculoskeletal pain have also been associated with low Vitamin D levels.

Vitamin D and calcium supplementation reduces the incidence of hip fractures, especially in menopausal women. Women of all ages with the lowest levels of Vitamin D in their blood had a 70% increased likelihood of fracture than those with the highest concentrations (even although the number of falls was the same in both groups).


Pre-eclampsia is a relatively common problem of pregnancy that is characterized by proteinuria (protein in urine), high blood pressure, and oedema. It can cause serious illness and even death in both pregnant mothers and their infants and is also a cause of premature delivery.

The exact cause of this condition is not clear, but it has been discovered that a vitamin D deficiency early in gestation increases the risk of developing pre-eclampsia five-fold. (University of Pittsburgh)

Eye problems (myopia) and crooked teeth problems may have their origins in utero if the pregnant mother has low levels of Vitamin D, and perhaps calcium.

Low Vitamin D levels contribute to infertility. Vitamin D is necessary for oestrogen production (in men and women).

Premenstrual syndrome (PMS) can be reversed by supplementing with Vitamin D, calcium and magnesium, as can menstrual migraines.


The risk of developing Type I diabetes is increased in people who are getting too little Vitamin D in childhood. In fact, the greater the amount of vitamin D supplied in the child’s diet (within reason, of course), the greater the benefit.

The cause of this type of diabetes is a malfunctioning pancreas which is unable to produce insulin. Frequently this is the result of an autoimmune disease where the person’s own immune system attacks the pancreas.

In addition, Vitamin D is essential for the biosynthesis and release of insulin. Glucose intolerance (a measure of the body’s ability to maintain the correct levels of sugar in the blood) is associated with the low concentrations of vitamin D in the blood. These are symptoms of Type II diabetes, so, vitamin D may protect against both Type I and Type II diabetes.


There is gathering evidence to suggest that inadequate Vitamin D and calcium levels might be a cause of obesity.

Sunlight (UV-B) or Vitamin D supplementation can normalise appetite, so reducing excessive food intake and normalising blood sugar levels. Unfortunately, some obese people tend to have an impaired ability to manufacture Vitamin D in their skin and also to absorb Vitamin D from the diet.

Calcium levels also play a role. A diet lacking in calcium results in an increase in the activity of the enzyme fatty acid synthase whose role is to convert calories into fat for storage purposes. Animal experiments have shown that increasing calcium intake can stimulate weight loss.

As noted before, there is a very close relationship between Vitamin D and calcium so it is not surprising that the interactions is seen here as well.


Many studies now link Vitamin D deficiency and the incidence of various cancers.

Dr Mercola goes so far as to say that “Optimizing your vitamin D levels can help you to prevent as many as 16 different types of cancer including pancreatic, lung, breast, ovarian, prostate, and colon cancers.

And vitamin D does not just impact your cancer risk slightly. It can cut your risk by as much as 60 percent!” and that any risks of sun exposure are far outweighed by the benefits.

The protective effects work in several ways, including:

o Increasing the self-destruction of mutated cells. If these cells are allowed to replicate tumours and cancer will result.

o Reducing metastasis (spreading of the cancer to other parts of the body). Patients with metastasized cancers are much more likely to die of the disease.

o Preventing the formation of new blood vessels which feed the tumour cells, causing them to become cancerous

o Protecting cells from oxidative stress by reducing free radical damage which leads to mutations and the development o cancerous cells.

o Causing cells to become differentiated rather than remaining undifferentiated cancerous cells.

o Researchers studying the link between Vitamin d deficiency and lung cancer believe that the vitamin causes the release of chemicals which, together with calcium, causes cells to stick more closely to one another, thereby preventing them from dividing uncontrollably.

In studies of breast cancer, 75% of patients were found to be Vitamin D deficient at the time of diagnosis. Furthermore, those who were deficient were much more likely to suffer from metastasis (spreading of the cancer to other parts of the body) and they were more likely to die of the disease.

Similar results have been found with other cancers including prostate and colon.

Brain function

Brain cells have many Vitamin D receptors on their surfaces, indicating an important role for the vitamin. More research is needed , but accumulating evidence suggests that:

o children with brain dysfunction are deficient in Vitamin D

o low Vitamin D levels increase depression and other mental disorders in older adults and the elderly

o low Vitamin D may contribute to chronic fatigue and depression.

o Seasonal Affective Disorder (SAD) has been treated successfully with vitamin D.

o People under high stress need to increase their intake Vitamin D and calcium.

o Parkinson’s disease and Alzheimer’s disease have been associated with lower levels of vitamin D.

o Vitamin D and calcium, together with an adequate diet and trace minerals has a positive effect in behaviour and learning disorders.

o Adequate vitamin D intake is essential for maintaining brain function later in life. Studies on 3000 European men found that the men with the highest levels of Vitamin D in their blood performed best on a test of mental function, including memory and information processing, while those with the lowest levels performed worst. Other research shows that Vitamin D protects ageing people from cognitive decline

Heart disease

Syndrome X is the name given to a collection of symptoms that tend to occur together: high blood pressure, obesity, diabetes and heart disease. Low levels of Vitamin D appear to be a cause of this syndrome.

Research also suggests that that vitamin D deficiency leads to deposits of calcium in the arteries (which leads to hardening of the arteries or atherosclerosis), joints, kidneys and maybe even the brain.

Conversely, supplementation with Vitamin D (or UV-B treatment) can lower blood pressure and lower cholesterol levels. Women with vitamin D deficiency have three times the risk for hypertension than women with high or sufficient levels.


To understand the importance of Vitamin D in immunity the following quote from Adrian Gombart (associate professor of Biochemistry and principal investigator with the Linus Pauling Institute at Oregon State University) is worth reading:

”Vitamin D is so crucial to the functioning of your immune system that the ability of vitamin D to boost immune function and destroy invading microorganisms has been conserved in the genome for over 60 million years of evolution.

The fact that this vitamin-D mediated immune response has been retained through millions of years of evolutionary selection, and is still found in species ranging from squirrel monkeys to baboons and humans, suggests that it must be critical to their survival, researchers say.

Vitamin D prevents the 'adaptive' immune response from over-reacting and reduces inflammation, and appears to suppress the immune response. However, the function of the new genetic element this research explored allows vitamin D to boost the innate immune response by turning on an antimicrobial protein. The overall effect may help to prevent the immune system from overreacting.

The existence and importance of this part of our immune response makes it clear that humans and other primates need to maintain sufficient levels of vitamin D”.

Vitamin D plays a role in regulation of both the "infectious" immune system and the "inflammatory" immune system. It promotes phagocytosis (the engulfing and removal of bad cells), anti-tumor activity, and is essential for a variety of functions that modulate the immune response.

Low vitamin D is associated with several autoimmune diseases including multiple sclerosis, Sjogren's syndrome, rheumatoid arthritis, thyroiditis and Crohn's disease. These are diseases caused when the immune system turns on itself – in other words it starts to malfunction.

Vitamin D deficiency is more than likely the main reason for seasonal outbreaks of the flu – rather than the flu virus itself which is almost certainly still around at other times of the year but unable to gain a foothold in people with healthy immune systems.

And Vitamin D supplementation can indeed have a protective effect. For example, psychiatric patients receiving 2,000 IU of vitamin D for several months were protected from a flu epidemic in the hospital. These were the findings of Dr. Cannell, a psychiatrist at Atascadero State Hospital in California who described Vitamin D as a potent antibiotic and antiviral agent.

In addition, Vitamin D prevents the immune system from producing a dangerous amount of inflammatory chemicals (cytokines) that attack sensitive respiratory membranes. Cytokines are an important part of your immune system. But in severe cases of the flu, their production spirals out of control, causing high fever and extreme fatigue. In fact, in most cases, this so-called "cytokine storm" is the actual cause of death.

The bottom line

It is almost certain that most people these days are short of Vitamin D.

Exceptions would be the rugged outdoors types like farmers and hunters – provided that they are in fact exposed to the sun at midday for a while, and not so thoroughly covered that they too are underexposed.

Taking a supplement would be a sensible protective action to take. Notably, both Vitamin D3 and Vitamin D2 (from plant sources, for example) can be used in supplements.

How much is enough?

The RDA is set at 200 IU of Vitamin D per day but higher levels are almost certainly better.

Studies have shown that adults supplied with up to 5000 IU per day will use the full supply, and natural production in the skin when exposed to reasonable sunlight is in the region of 20 000IU per day. Perhaps the body knows best what it needs?

Current research supports the idea that 4,000 IU per day, from all sources, is about optimal. Assuming you get some (but not a lot) of sun exposure daily, then you probably only need to consume about 2,000 IU per day from food and supplements. Certainly 1000 IU per day would be safe.

Many naturopathic physicians go even further stating that anywhere between 4,000 IU and 10,000 IU a day is appropriate.

Vitamin D is not dangerous nor is it particularly toxic – but one needs to be sensible. It has a therapeutic index of 10 which means that it is considered by the Vitamin D Council to be twice as safe as water in terms of "overdosing".

In other words, this vitamin is safe and beneficial in the relatively large amounts that nature intended!

Of course, the best way of knowing your Vitamin D status is to actually have a blood test for levels of 25-hydroxyvitamin D [25(OH)D] – twice a year or at least once a year.

Normal healthy levels are taken to be 45-55 ng/ml. Acceptable levels are between 35-35 ng/ml and optimal levels 55 ng/ml.

Levels below 35 ng/ml means you are deficient, and 100 ng/ml is regarded as excessive with greater levels being toxic. But in most ordinary circumstances this is probably not necessary.

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