Vitamin D

What is Vitamin D?

Vitamin D is actually a hormone and one of the oldest ones at that, rather than a vitamin as it’s name suggests.  To be ultraspecific, it’s a group of fat soluble prohormones, meaning that the body turns them into the active hormonal form when it needs to.

What is the difference between a hormone and a vitamin?  A vitamin is a substance that an organism needs in order to survive and that it cannot manufacture in sufficient quantities endogenously or within itself.  It must therefore be obtained through the diet.  A hormone is a chemical produced by a cell or cells in the body that has a physiological action on other parts of the body.  It’s like a chemical messenger from one part of the body, telling another part of the body what to do.

Vitamin D has been produced by different life forms in response to sunlight exposure for over 750 million years.  Humans are hardly unique in their ability to manufacture this substance, as the majority of plants and animals, even phytoplankton and zooplankton will manufacture Vitamin D in response to sunlight exposure.

Although the signs of Vitamin D deficiency were first described in medical literature as early as the 17th century, and some indications of awareness of the effects of Vitamin D have been described from early antiquity, Vitamin D was first properly identified in 1921 making it the 4th ‘vitamin’ to be discovered, and hence it was named after the 4th letter in the alphabet.  Initially researchers discovered that vitamin D was present in certain fats, so they considered it to be a vitamin.  It wasn’t until 1923 that researchers discovered that when skin was irradiated with sunlight or UV light, that the skin itself produced a substance identical to ‘the fat soluble vitamin’ as it was then known.  In 1928, another researcher by the name of Adolf Windaus discovered the precursor to vitamin D and was awarded the Nobel Prize for Chemistry for his discovery.  Professor Windaus later determined the chemical structures of the compounds which made up the ‘vitamins D’ at the University of Göttingen in Germany.

Vitamin D deficiency is common in women with PCOS and contributes to the symptoms

Vitamin D deficiency occurs in a very high percentage of women with PCOS, over 70%, and appears to be a contributing factor to some of the biochemical abnormalities seen in the condition such as irregular menstruation and infertility.  Increasing Vitamin D levels has been shown to improve insulin sensitivity and help in the treatment of obesity.  Researchers at the Medical University of Graz in Austria have found that low Vitamin D levels correlate with the occurrence and severity of belly fat, weight gain, high blood pressure, elevated blood sugar levels, insulin resistance, elevated insulin levels, elevated triglycerides and high cholesterol levels.

In a study of 13 women with PCOS, 8 were found to have a degree of vitamin D deficiency – some quite severe.  All 13 women were treated with vitamin D2 (not the recommended form of Vitamin D by the way D3 is much much better) at a dose of 50,000 IU once or twice a week, and also received 1,500 mg of supplemental calcium per day.

Nine women in the study had either irregular or completely absent menstruation prior to the study.  After Vitamin D supplementation 7 had their cycles return and/or normalise within 2 months and … here’s the good bit … the 2 who didn’t have their cycles return or normalise … were pregnant!  Any incidences of dysfunctional uterine bleeding also resolved within 2 months of Vitamin D supplementation.

Other studies have also shown that a percentage of women with polycystic ovary syndrome had sub-optimal levels of vitamin D. Low vitamin D has been clearly linked to insulin resistance and obesity.

Have Your Vitamin D Levels Checked First

As Vitamin D is a fat soluble vitamin, it is possible to accumulate too much of it through oral supplementation.  Your body has natural regulatory mechanisms in place to ensure that you never create more Vitamin D from sunshine than you need, but when you supplement with Vitamin D, you override this.  Therefore, it is best to have your Dr test your Vitamin D levels before you begin supplementation.

The test to ask for is 25(OH)D or 25-hydroxyvitamin D. There is another test that they do called 1,25(OH)D but this is not as good a marker of functional Vitamin D deficiency as it measures a biologically inactive form of vitamin D. The test I recommend measures the level of activated Vitamin D, rather than a non-active precursor.

Note that there are two units of measurement for Vitamin D – nmol/L and ng/mL.  For Vitamin D 1.0 nmol/L is equivalent to 0.4 ng/mL.  The most common way is ng/mL and that is what I shall use in this article, however, if you are in a country where it is measured in nmol/L, all you need to do is multiply the figures in this article by 2.5 to get the equivalent in nmol/L or multiply your test results by 0.4 to convert them to ng/mL.

How Much Vitamin D do I Need?

The optimum level of 25(OH)D is between 50-65 ng/ml. If it is less than this, you increase your risk of certain diseases.  For treatment of specific conditions which respond to Vit D, levels can be as high as 95 ng/ml. Symptoms of excess or toxicity have not been demonstrated at levels below 200 ng/ml. Old ranges can state that as little as 20 ng/ml is ok, which is the point at which serious symptoms of deficiency can begin.

Most adults will require a minimum of 5000 i.u. per day to achieve this.  Studies have shown that supplementation of 10,000 i.u. daily did not cause any toxic side effects, though everyone is different and it is always wise to have your Vitamin D levels checked by a laboratory prior to commencing supplementation.

Steady-state serum 25(OH)D concentration will rise by 0.7 nmol/L for every 1 ng or 40 i.u. of oral Vitamin D3 given daily.  As a general rule, every 100 i.u. of Vitamin D3 taken orally will raise the level of Vitamin D circulating in the blood by approximately 1 ng/ml when taken every day.

How Can I Get Vitamin D?

If you live in an area where you can get adequate amounts of sunshine to allow your body to produce adequate Vitamin D and you have the time to do this in a safe manner – no sunscreen and spending at least 10-20 minutes a day every day in the sun which as much of your skin exposed to the sun as possible, then this is obviously the best method, however many of us don’t have that luxury.  Either we live in an area which does not get adequate sun exposure, or our lives are so busy that they don’t permit us to spend a sufficient amount of time lolling about in the sun.

The actual amount of time needed for each person varies enormously, depending upon their skin colour, degree of tanning and the geographical location of where they live. The darker your skin, the less Vitamin D you will produce in a given amount of time compared to someone with lighter skin.  It is important to note that getting an adequate amount of sunshine for therapeutic Vitamin D production is a very different proposition to going and baking in the sun for several hours to get a tan.  Whilst several episodes of time in the sun each day is beneficial, these periods of time should be sufficiently short that your skin NEVER develops a pinkish tinge.  This is a sign of skin damage and as all the skin cancer prevention advertisements on television make quite clear – this is a bad thing.  Something which researchers have only just discovered, however, and which goes against the traditional advice given by skin cancer authorities is that sun exposure in the middle of the day is actually more beneficial than at any other time of day as the ratio of UVB to UVA radiation is highest and you therefore require a shorter amount of time spent in the sun to achieve optimal 25-hydroxyvitamin D production.

Oral Supplementation

If you need to supplement with Vitamin D be aware that there are two different kinds.  If you stay away from ergocalciferol (D2) the synthetic form of Vitamin D which can be toxic at high doses, and instead choose cholecalciferol (D3) the natural form extracted from fish oil and also the kind found in eggs, organ meats like liver, fish etc, you will be highly unlikely to have any toxic effects.

Other Benefits of Having Optimal Vitamin D Levels:

Scientists are just now beginning to glimpse the body’s ubiquitous need for Vitamin D.  Since 1970 in excess of 9700 scientific papers have been published on some aspect or another of Vitamin D.  Not surprisingly, 400 of them have been in relation to it’s role in preventing and treating osteoporosis.  A further 250 have been in relation to the significant relationship between Vitamin D levels and reduced occurrence of various forms of cancer.  Almost all cells in the human body across 36 different organs including fat cells, pancreatic beta cells, the ovaries and uterus, have a receptor for Vitamin D!  This means that Vitamin D is involved in practically all processes within the body and this explains why deficiency in this vital nutrient can have such far reaching repercussions to our state of health and wellbeing.  So far, we know that having an optimal level of Vitamin D:

  • Decreases the risk of mortality (death) from ALL causes
  • Reduces the risk of cardiovascular disease, particularly in relation to blood pressure, cholesterol & triglyceride levels
  • During pregnancy reduces the occurrence of asthma in early childhood
  • Reduces the risk 0f many types of cancer including breast, prostate and colorectal cancers
  • Greatly improves the function and regulation of the immune system
  • Restores pancreatic secretion of insulin where it has been inhibited
  • Is associated with lower levels of insulin resistance, type II diabetes and poor blood sugar control
  • Improves brain function
  • Improves bone density in combination with calcium

Conversely, Vitamin D deficiency has been associated with an absolutely phenomenal number of diseases including:

  • Addison’s Disease
  • Allergic Hypersensitivity
  • Alzheimer’s Disease
  • Ankylosing Spondylitis
  • Asthma
  • Autism
  • Autoimmune illness
  • Benign Prostatic Hyperplasia
  • Bladder Cancer
  • Brain Cancer
  • Breast Cancer
  • Cancer
  • Coeliac Disease
  • Cerebral Palsy
  • Chronic Obstructive Pulmonary Disease (COPD)
  • Chronic Pain
  • Cognitive Function
  • Colon & Rectal Cancer
  • Cystic Fibrosis
  • Depression and Seasonal Affective Disorder (SAD)
  • Diabetes
  • Endometrial Cancer
  • Epilepsy
  • Eye Cancer
  • Gastrointestinal Function
  • Gaucher’s & Fabry’s Disease
  • Graves’ Disease
  • Hashimoto’s Thyroiditis
  • Heart Disease
  • Hypertension
  • Inflammatory Bowel Disease
  • Influenza
  • Innate and Adaptive Immunity
  • Liver Cancer
  • Liver Function
  • Lung Cancer
  • Lymphoid Cancer
  • Melanoma
  • Mental Illness
  • Mineral metabolism
  • Mortality
  • Multiple Sclerosis
  • Muscle Weakness & Falls
  • Obesity
  • Osteoarthritis
  • Osteomalacia
  • Osteopaenia
  • Osteoporosis
  • Otosclerosis
  • Ovarian Cancer
  • Pancreatic Cancer
  • Parathyroid Function
  • Parkinson’s Disease
  • Premenstrual Syndrome
  • Prostate Cancer
  • Renal Function
  • Rickets
  • Sarcoidosis
  • Sickle Cell Disease
  • Skin Cancer
  • Stroke
  • Tuberculosis
  • Turner Syndrome

One of the most well-regarded research scientists in the area of Vitamin D is Anthony W Norman.  He was written myriad articles on the subject and collated a great deal of historical research on Vitamin D into a concise and easily readable form.


Vitamin D3 is one of the safest substances known to man – overdose of vitamin D3 doesn’t occur until more than 100 times the daily RDA has been taken every day for several months. Acute, one-time overdoses require over 50 mg of Vitamin D3 to be taken orally in one dose.  This is equal to about 100 bottles of Vitamin D3 supplements or10,000 times the RDA. Formal toxicity studies on animals have indicated that signs of toxicity begin at 20,000 i.u. per kilogram! That’s absolutely huge.

The oral LD50 (lethal dose 50% or the amount necessary to kill half the animals in a study) for Vitamin D3 or cholecalciferol in dogs is about 88 mg/kg, or 3,520,000 IU/kg, again an absolutely mind-boggling amount.  A 165 lb adult human would need to take 660,000 capsules containing 400 i.u. of Vitamin D3 to achieve this and frankly I think their stomach would literally explode well before any vitamin D poisoning occurred!

The only documented case of pharmacological poisoning or overdose from Vitamin D3 relates to a man who consumed between 156,000–2,604,000 IU of cholecalciferol a day for 2 years, due to a manufacturing problem with a supplement called Prolongevity, where the supplement actually contained as much as 430 times the amount of Vitamin D3 that it stated on the label.  Even in such an extreme case, once the unfortunate fellow was properly diagnosed and treated, he recovered uneventfully.

It is a different story with the synthetic form of Vitamin D, ergocalciferol or D2.  It is not recommended that Vitamin D2 be taken as a nutritional supplement for this reason.

More information:

Thys-Jacobs S, Donovan D, Papadopoulos A, Sarrel P, Bilezikian JP. Vitamin D and calcium dysregulation in the polycystic ovarian syndrome. Steroids 1999;64:430-435.

Armas LAG et al, Vitamin D2 is much less effective than vitamin D3 in humans. J Clin Endocrinol Metab 2004;89:5387-5391.

Chiu, KC et al, Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction, Am. J. Clinical Nutrition, May 2004; 79:820-825

Borissova AM et al, The effect of vitamin D3 on insulin secretion and peripheral insulin sensitivity in type 2 diabetic patients. Int J Clin Pract 2003;57:258-261.

Norman, A. W. 2008. From vitamin D to hormone D: Fundamentals of the vitamin D endocrine system essential for good health. Am. J. Clin. Nutr. 88:491S–499S

Hathcock JN et al. Risk Assessment for Vitamin D Am J Clin Nutr. 2007;85:6–18

Wehr E et al, Association of hypovitaminosis D with metabolic disturbances in polycystic ovary syndrome, Eur J Endocrinol. 2009 Oct;161(4):575-82

Raghuramulu N et al, Vitamin D improves oral glucose tolerance and insulin secretion in human diabetes. J Clin Biochem Nutr

Panidis, D et al, Serum parathyroid hormone concentrations are increased in women with polycystic ovary syndrome, Clin Chem, 2006, 51(9):1691-7

Hahn, S et al, Low Serum 25-Hydroxyvitamin D Concentrations are Associated with Insulin Resistance and Obesity in Women with
Polycystic Ovary Syndrome, Exp Clin Endocrinol Diabetes. 2006 Nov;114(10):577-83

Vitamin D: Physiology, Molecular Biology, and Clinical Applications, Anthony W Norman edited by Michael F Holick, 1999 Humana Press, Inc, Totowa, NJ (457 pages, Hardcover book)


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