The importance and the challenging role of vitamin D in the 21st Century

Table of contents

  1. Introduction
  2. The importance of Vitamin D and its health benefits
  3. The Vitamin D deficiency epidemic and the challenges surrounding sunlight exposure in avoiding vitamin D deficiency
  4. Testing for Vitamin D deficiency and sufficiency and methods of raising serum vitamin D levels
  5. Vitamin D levels from individual cases in different environments
  6. Summary and conclusion
  7. Appendix 1
  8. References

1.0   Introduction

My dissertation will be looking at the importance and the challenging role of vitamin D in the 21st century. The health benefits of vitamin D have long been known to doctors, scientists and health professionals for many years. Much of the findings from earlier studies surrounding vitamin D were based on the nutritional role of vitamin D in supporting and enhancing calcium absorption and bone health as opposed to other genomic functions which were relatively unknown until in the last ten years when scientists and doctors were able to have the technical ability to research this steroid hormone precursor (as opposed to a vitamin) further and explore many of the other genomic functions that are linked to vitamin D. The first part of my report will look at some of the health benefits of vitamin D that have been found from studies over the last 10 years and why it is one of the most important and oldest prohormone known to mankind.

The second part of my report will focus on the global epidemic crisis surrounding vitamin D deficiency. Vitamin D deficiency is now considered to be a worldwide problem that is being witnessed even in countries that are closer to the equator. Many health experts continue to advise people to increase their exposure to sunlight and in this section I will be exploring some of the challenges surrounding raising vitamin D levels via ultra violet radiation from sunlight exposure.

The third part of my report will look at some of the blood test laboratory ranges which can confirm vitamin D deficiency and the correct serum vitamin D levels required in order to remain vitamin D sufficient. I will be exploring some of the other methods of raising vitamin D levels in order to avoid vitamin D deficiency besides sunlight exposure.

The fourth part of my report will look at some examples of individuals who have experimented with sunlight exposure in raising their serum vitamin D levels.

The last part of my report will conclude with a summary of the increasing difficulties and challenges that we all face in avoiding vitamin D deficiency particularly through sunlight exposure. I will summarise my thoughts on why conventional advice on vitamin D from government and many health professionals may not be enough to address the current global crisis that we have with vitamin D deficiency.

2.0   The importance of Vitamin D and its health benefits

Historically most health experts had associated vitamin D deficiency with rickets in children, osteoporosis, bone disease and in enhancing the absorption of calcium and magnesium. However research over the last ten years has found some incredible studies on vitamin D. In 2001 scientists first completed the human genome sequence and estimated that the human body has about 27,000 genes and since then estimates have varied from one source to another over this number with somewhere between 20,000 to 30,000 genes in the human body. According to one well documented study on PubMed that is contributed from Eric Lander reveals that the human body has about 20,500 genes[i]. According to the Vitamin D Council vitamin D is known to influence almost 3,000 of these genes and a study from the Reproductive Biology and Endocrinology on PubMed seems to confirm this theory[ii][iii]. One of the most important studies that I have found over the years regarding the health benefits of vitamin D is its effectiveness and protection it can provide against many different types of cancer. In fact there are already over 800 references that have been documented on the effectiveness of vitamin D with cancer[iv]. According to one study from one of the leading experts in the field of vitamin D Dr William Grant, vitamin D can influence as many as 16 different types of cancers despite the study revealing some inconsistent results between bladder, lung and pancreatic cancer with UVB radiation[v].

Vitamin D deficiency has been linked to a number of other health conditions besides cancer. This includes diabetes which has been closely linked with vitamin D deficiency with some data from the human observational studies showing that deficiency in vitamin D can contribute towards the development of type 1 diabetes[vi].  On the other hand a study of 126 individuals in California (US) showed that insulin resistance is closely related to vitamin D deficiency. [vii]

There are a number of sources that reveal how hypovitaminosis D (also known as vitamin D deficiency) is strongly linked to number of autoimmune disorders such as crohn’s disease, multiple sclerosis and rheumatoid arthritis. [viii] Whilst the role of vitamin D in influencing and stimulating the functions of T-cells is well understood according to one report from the Harvard Medical School which evaluated 1446 studies that examined the role of vitamin D and the prevention of autoimmune diseases, there still appears to be a lack of prospective interventional evidence of the role of vitamin D in the prevention of autoimmune diseases.[ix]

Some of the other health conditions which vitamin D deficiency has been linked to include:

  • Heart Disease [x]
  • Fatigue [xi]
  • Depression [xii]
  • Seasonal Affective Disorder [xiii]
  • Obesity [xiv]
  • Syndrome X [xv]
  • Infertility and PMS [xvi][xvii]

Several studies have shown the link between Vitamin D deficiency with many health conditions in humans however from some of the evidence given in my report so far, it can partly explain the importance role of vitamin D and remaining vitamin D sufficient. In the 21st century particularly in the west, we have witnessed many individuals presenting with some of the health conditions as described so far in the report. Our human evolutionary history suggests that these health conditions were relatively unknown to most people when our ancestors many hundreds and thousands of years ago stayed largely outdoors and exposure to UVB rays from the sunlight was much more constant. The wearing of clothes was minimal and most probably large amounts of their skin were most likely exposed to the sun and possibly reaching optimal levels of serum vitamin D. The average person today in evolutionary terms spends a lot of time sitting indoors in a chair in an office or at home under fluorescent light bulbs and perhaps this could help us to understand to some extent why we are witnessing an epidemic of vitamin D deficiency in the modern era.

3.0   The Vitamin D deficiency epidemic and the challenges surrounding sunlight exposure in avoiding vitamin D deficiency

Many studies and experts views on recommendations over  the length of time the skin needs to be exposed to UVB rays from the sunlight in order to produce vitamin D vary but most seem to agree that approximately 15 minutes of sunlight exposure three times a day is required in order to avoid vitamin D deficiency. Despite this, we have a global world wide vitamin D deficiency issue with increasing evidence that many people particularly from the Middle East, Asia and even South America where there is abundance of sunshine and vitamin D synthesis available all year around, we are still witnessing some of the lowest levels of vitamin D and highest rates of hypovitaminosis D within those regions that are closer to the equator. According to one study conducted by the College of Medicine in Saudi Arabia, a study of 31 Saudi Arabian women confirmed despite abundant of sunshine, social customs and urbanisation could partly explain why many of these women involved in the study were vitamin D deficient.[xviii] In India, a study by the All India Institute of Medical Sciences in New Delhi found that vitamin D deficiency was prevalent even in South India States and sunshine exposure alone can’t fully justify the vitamin D deficiency epidemic in India[xix]. According to world renowned vitamin D expert Dr Michael Holick approximately over one billion people worldwide are vitamin D deficient and this has now become a global health problem.[xx] Evolution, social customs or industrialisation could help us to partly understand the vitamin D epidemic however the complexity surrounding using UVB rays from the sunlight in raising serum vitamin D levels needed to be further examined.

When the UVB rays from the sun come in contact with the skin, the cholesterol in the skin converts these rays into vitamin D3 or also known as cholecalciferol. From the skin, cholecalciferol is converted into calcidiol (25-hydroxyvitamin-D) by the liver. Once this is circulated in the blood, it is converted into calcitriol (1,25-dihydroxy Vitamin D) by the kidneys.

Some of the studies that I have looked into gave me an insight into many of the factors that could affect ones ability to raise their serum vitamin D levels from UV radiation from sunlight exposure. These include:

  • Skin colour and pigmentation – individuals with lighter or pale skin generally require less sunlight exposure than those individuals with darker skin. Individuals with darker colour skin may require an hour or two of sunlight exposure to reach optimal levels as opposed to individuals with light coloured skin who may require around 20 minutes of sunlight exposure 3 times a week.[xxi]
  • Weather – clouds can filter some of the UV radiation so less UVB rays could reach the earth’s surface
  • Pollution – pollution in the air can filter UV radiation from the sun particularly if there is a lot of ozone in the air pollution. Cities or places where there are a lot of buildings surrounded together can be affected by this.
  • UVB rays are considered to be only available when the UV Index is at least 3 or above. This means even winter sunshine during the winter season for those living at much higher altitudes is not enough as the UV radiation is generally below 3.
  • Many experts such as Dr Mercola and Dr M. Holick recommend optimal times for vitamin D production to be around midday. The recommendation is that UVB rays are considered to be at their strongest between the hours of 10am through 2pm and this is the ideal time to take advantage of UVB rays in raising vitamin D levels. I have not been able to verify this information or find any credible evidence from PubMed or other sites of any useful studies which have shown some evidence of this. The only information I was able to establish was an Interview conducted by Dr Mercola with Carole Baggerly (Director and founder of GrassrootsHealth) in 2011 quoting the following:

“When we did a scientific test of what it’s going to take to get enough sun in San Diego… at my age – age is a factor in how much you absorb – we came to a test conclusion that it was going take 15 to 20 minutes a day in the prime time of UV, between 10 am and 2 pm, each and every day… with 40 percent of my body exposed.  … I encourage people to take advantage of the sun.  The only message I have about the sun is: don’t burn.  That’s it.”

Source: http://mercola.fileburst.com/PDF/ExpertInterviewTranscripts/InterviewCaroleBaggerlyVitaminD.pdf

  • At least 40% of the skin surface should to be exposed in the sun in order to raise enough vitamin D in order to avoid vitamin D deficiency. This should include not just the hands and arms but also the torso or the legs.  The facial skin produces very little vitamin D and needs to be protected from the sun in order to avoid skin damage to the delicate skin around the face and prevent premature wrinkling. [xxii]
  • Latitude and altitude – The closer to the equator, the better as sunlight is usually stronger closer to the equator. UV radiation is much higher the closer you are to the equator. Individuals with dark skin living at higher latitudes are generally speaking at a higher risk of vitamin D deficiency.
  • Clothing – the more clothes one wears, the less area of the skin is exposed to the sun so there is a chance of raising serum vitamin D levels.
  • Sunscreen – The use of most sunscreen blocks can reduce one’s ability to produce vitamin D. [xxiii] An SPF of 8 or less could block up to 95% of vitamin D production.
  • Bathing or showing – Originally in one of Dr Micheal Holicks earlier studies many years ago he revealed that bathing and showering withi soap soon after the skin’s surface has been exposed to sunlight exposure could enable the individual to lose the benefits of vitamin D production. More recently Dr Mercola has claimed that new research shows that individuals should wait at least 48 hours after sunlight exposure.[xxiv] Vitamin D does not not penetrate immediately from the skin and into the bloodstream and how long it can actually take is rather questionable in my view . I have not be able to find any useful studies or trials on PubMed to verify these claims.

Some of the other factors that could affect serum vitamin D levels include age, cholesterol levels and obesity. Obese individuals are likely to experience poor bioavailability due to large amounts of deposition of vitamin D in the body fat stores.[xxv]

Age can also play a factor in vitamin D deficiency particularly in older people due to lack of dietary measures such as low consumption of oily fish food as well as large amount of time spent indoors in later life and lack of sunlight exposure particularly in winter for those individuals based in northern altitudes. [xxvi]

Given that cholesterol is the precursor for the production of vitamin D3, low levels of cholesterol could affect vitamin D3 production.

4.0   Testing for Vitamin D deficiency and sufficiency and methods of raising serum vitamin D levels

In order to establish whether one is vitamin D deficient or not a serum vitamin D test would be the starting point. The correct test is known as 25-Hydroxyvitamin D or 25 (OH) D. It is widely believed that this test is a better overall marker of serum vitamin D levels. Currently there appears to be no one universally accepted serum level for vitamin D deficiency. Much of the earlier studies that I had examined showed that an individual with serum vitamin D levels below 40ng/ml would be regarded as being vitamin D deficient. GrassrootsHealth, an organisation leading in the field of vitamin D research state that at least 40 researchers/practitioners agree that serum vitamin D levels should at least be 40ng/ml in order to be vitamin D sufficient[xxvii]. However other sources such as the Vitamin D Council believe that this level should be much higher as much as 50ng/ml in order to be vitamin D sufficient. Laboratory ranges vary from one source to another. According to Dr Michael Holick vitamin D laboratory reference ranges for vitamin D are as follows for optimum human environment:

  • Vitamin D – 25 Hydroxy D
  • Deficient – Less than 50ng/ml
  • Optimal – 50-70ng/ml
  • Treatment of heard disease or cancer – 70-100ng/ml
  • Excess – greater than 100ngml

Source: Holick MF. Calcium and Vitamin D Diagnostics and Therapeutics. Clinical Lab Med. 2000 Sep; 20(3):569-90)

There have been various theories presented by many researchers on dosages required in order to raise vitamin D levels at accepted levels. The exact dosage of vitamin D that an individual would require in order to avoid vitamin D deficiency would vary from person to person. One of the pioneers in the field of vitamin D for over the last 30 years Dr Michael Holick believes 100IU of vitamin D should raise serum vitamin D levels by 1ng/ml. Going by this theory and if we assume 40ng/ml is the accepted level that most of us should strive for, this would suggest that the average person would need 4,000IU’s of vitamin D in order to raise their vitamin D levels in order to avoid vitamin D deficiency (assuming all other factors remain constant). On the other hand current research from GrassrootsHealth suggests that most adults need approximately 8,000IU’s of vitamin D a day in order to raise serum vitamin D levels above 40ng/ml. The first step in determining the dosage required would be to monitor the serum vitamin D levels. If the levels are too low, the individual can use one of the following four methods in raising their serum vitamin D levels. These are as follows:

  • Sunlight exposure
  • Safe Tanning bed
  • Oral supplementation
  • Food such as salmon and cod.

Sunlight exposure – the human body was made to adapt to the natural environment with adequate exposure to sunlight[xxviii]. Ultra Violet Ray B from the sun on clear days in equilateral latitudes can provide as much as 20,000IU of vitamin D and provide all the necessary vitamin D for humans in order reach optimal levels. [xxix] Once the body has produced all the necessary vitamin D it requires, our body has mechanisms in place whereby it will automatically stop producing any further vitamin D from sunlight. When the skin turns into the lightest shade of pink this is often a good indication that the individual no longer needs to continuously expose large amounts of their skin to the sun and to minimise the risk of burning. [xxx]

Safe tanning bed – Artificial ultra violet light from a tanning bed with the use of new form of electronic ballasts can reduce or eliminate the risk of electronic magnetic frequency radiation that are often generated by standard tanning beds with magnetic ballasts. These are considered to be not only safe and fully approved by the Vitamin D Council but economical to run. [xxxi] [xxxii]

Oral supplementations can be useful in meeting the daily requirements of vitamin D where regular natural sunlight and a safe tanning bed isn’t available to the individual. Unfortunately supplementation doesn’t provide the same benefits as natural sunlight as it is non-sulfated and can not be converted to vitamin D sulfate. [xxxiii] The other difficulty with oral supplementation is that there is no way of knowing whether one has achieved the right serum vitamin D levels without a blood test. Vitamin D toxicity can occur if the dosage is too high and as vitamin D is a fat soluble vitamin, vitamin D toxicity is not easy to reverse.

Foods such as oily fish such as wild salmon contain some vitamin D however the levels are usually very low around 500-1000 IU’s of vitamin D and farmed fish containing just a few hundred IUs. An individual would need to eat a few salmons a day just to meet their daily requirements of vitamin D. There are other factors that need to be considered such as risk of exposure to mercury and as well as other toxic chemicals from fish which can increase the risk of other health problems. [xxxiv]

5.0 Vitamin D levels from individual cases in different environments

On the 17th August 2012 I had asked two people who are closely related to me to undertake a 25 Hydroxyvitamin D test with Thyrocare in India (http://www.thyrocare.com/). For this example purposes I will refer to the first person as person 1 and the 2nd person as person 2.  Both individuals are from India and have lived there since birth. They work as self-employed in a factory and between the months of March and August 2012 both individuals had spent around 30-45 minutes approximately in the sun around 3 or four times a day. The hands, arms and parts of their legs were all exposed in the sun at the back of their garden usually around midday. The first person (28 year old male) took no vitamin D3 supplements and the second person (67 year old male) took an additional 3,000IU of vitamin D3 a day on the advice of his doctor.  I had received their blood test results (see appendix 1) of their serum vitamin D levels. The first person had a reading of 20.85ng/ml and the second person had a reading of 45.1ng/ml. Despite the additional 3,000 IU of vitamin D3, it’s not clear just how much of person 2 serum vitamin D levels were raised by sun exposure however the first person’s blood test results clearly show that he is deficient in vitamin D despite plenty of exposure to sunlight. There may be several reasons why despite adequate exposure to sunlight, both individuals were unable to get their serum vitamin D levels high enough. One possibility is that the high level of air pollution in India could be filtering out a lot of the UV radiation from the sun and could partly explain why there is a wide scale vitamin D deficiency in India.

On the other side of the world in the US, Kevin Gianni (Health Advocate and owner of the website Renegade Health) claims that he struggles to keep up his vitamin D levels despite spending a lot of time in the sun. His recent test results posted on his own blog reveals a reading of just 25.2ng/ml which again indicates vitamin D deficiency[xxxv].  I have not been able to establish from his blog whether he took into consideration the points I raised in chapter 3 my report regarding the factors affecting UV radiation from sunlight exposure such as how much of the skin surface was exposed to the sun, what time of the day or length of time in the sun.

6.0 Conclusion

There are various theories put forward by many different researchers supporting the positive effects of sun exposure against many diseases. Given that it has only been in the last ten years or so that researchers have had the technical ability to research vitamin D much further, I believe that there still needs to be much further randomised clinical trials surrounding sunlight exposure and its role in preventing various diseases and promoting health. Much of the research that I have read appears to be from observational studies as opposed to interventional studies and I think most probably the interventional studies will require much further and larger studies to be carried out over a much longer time period. However at present researchers must make use of well conducted observational studies that are currently available. GrassrootsHealth are one of the few organisations currently campaigning to solve the vitamin D deficiency epidemic and are currently undertaking a major five year international public health project. The findings from the project most probably won’t become available to the public until 2017 once the 5 year project comes to an end but it is a step in the right direction in educating more people of the importance of vitamin D and getting their serum vitamin D levels checked regularly.

Individuals must take several factors into consideration when attempting to use UV radiation from the sun in raising their serum vitamin D levels. The standard fifteen to twenty minutes sun exposure three times a week rule that most researchers advocate is a good starting point for most people however as outlined in my report there are various different factors that could affect one’s ability in producing vitamin D from sunlight exposure and these should be taken into consideration.

In attempting to solve the current global vitamin D epidemic crisis, I believe first and foremost governments need to be able to make vitamin D testing much more easily available and affordable for people. Unfortunately for most people the only option at present is to undertake a 25 Hydroxyvitamin D test either through a private health insurance or to just to pay for the test at a clinic. In most cases particularly here in the UK, some private clinics would refuse such testing without a referral from the patients GP. One idea is perhaps vitamin D testing could become part of the standard blood test (such as Complete Blood Count) that most doctors refer patients to when making a patient referral to a laboratory clinic. The difficulty at the moment is the cost. Serum 25 Hydroxyvitamin D assays are expensive and it may take some time perhaps a few years or longer before the cost of 25(OH)D assays fall but essentially I feel the cost may perhaps need to be subsidized by governments if they are to become more easily affordable and cost effective to people. This seems increasingly unlikely in the current economic climate but it remains to be seen what governments in each country do in the foreseeable future in working together in overcoming this global epidemic crisis. As mentioned earlier organisation’s like GrassrootsHealth are leading the way in educating people all across the world the importance of vitamin D and the more people that can sign up to this initiative, the greater the pressure that could be exerted on government officials worldwide to make the necessary changes to help solve this epidemic.

There won’t be any easy solution to solving this crisis as evolution, industrialisation or social customs among other things do play a role in the current global vitamin D deficiency epidemic but educating people to make the necessary small and gradual measures that they can take in overcoming vitamin D deficiency will be critical. If getting adequate sunlight exposure is not an option for most people, oral supplementation or the use of a safe tanning bed could be considered. The market for safe tanning bed with the new safer electronic ballasts is still relatively new and expensive. Oral supplementation and regularly monitoring of serum vitamin D levels would require the patient to work closely with a physician. There are some theories from some researchers on mega dosing on vitamin D3 supplements to bring serum vitamin D levels up for a limited period followed by a maintenance phase however it must be emphasized that the patient must consult their General Practitioner or a fully qualified practitioner who specialises in this field before starting any new initiative of such kind.

Essentially if more governments or health organisations do invest in educating people the importance of vitamin D and tackling the current global vitamin D deficiency epidemic, individuals themselves will also have to play their part in firstly deciding what is important for them in life before we can together solve this crisis.

7.0 Appendix 1

Person 1: 28 year old/Male

Test Name Method Value Units
25-OH Vitamin D Total C.L.I.A 20.85 Ng/ml
ANY

Person 2: 67 year old/Male

Test Name Method Value Units
25-OH Vitamin D Total C.L.I.A 45.1 Ng/ml
ANY

8.0 References

[i] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2148306/
[ii] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3239848/#B145
[iii] http://www.vitamindcouncil.org/about-vitamin-d/what-is-vitamin-d/
[iv] http://mercola.fileburst.com/PDF/703-highly_cited_vitamin_D_cancer%5B3%5D.pdf
[v] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2715209/
[vi] http://jn.nutrition.org/content/135/2/323.long
[vii] http://www.ncbi.nlm.nih.gov/pubmed/15113720
[viii] Cantorna MT. Vitamin D and autoimmunity: Is vitamin D status an environmental factor affecting autoimmune disease prevalence? Proc.Soc.Exp.Biol.Med. 2000;223:230-3
[ix] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3098920/
[x] Segall JJ. Latitude and ischemic heart disease [letter]. Lancet 1989;1:1146.
[xi] Puchacz E, Stumpf WE, Stachowiak EK, Stachowiak MK. Vitamin D increases expression of the tyrosine hydroxylasegene in adrenal medullary cells. Brain Res. Mol. Brain Res. 1996;36:193-6.
[xii] Gloth FM 3rd, Alam W, Hollis B. Vitamin D vs. broad spectrum phototherapy in the treatment of seasonal affective disorder. J Nutr Health Aging. 1999;3(1):5-7.
[xiii] Gloth FM, III, Alam W, Hollis B. Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. J.Nutr.Health Aging 1999;3:5-7.
[xiv] Cantorna MT. Vitamin D and autoimmunity: is vitamin D status an environmental factor affecting autoimmune disease prevalence? Proc.Soc.Exp.Biol.Med. 2000;223:230-3
[xv] Henendez C, Lage M, Peino R, Retinoicacid and vitamin D(3) powerfully inhibit in vitro leptin secretion by human adipose tissue. J Endocrinol. 2001 Aug;170(2):425-31
[xvi] Panda DK, Miao D, Tremblay ML, Targeted ablation of the 25-hydroxyvitamin D 1alpha -hydroxylase enzyme: evidence for skeletal, reproductive, and immune dysfunction. Proc Natl Acad SciU S A. 2001 Jun 19;98(13):7498-503.
[xvii] Thys-Jacobs S. Micronutrients and the premenstrual syndrome: the case for calcium. J.Am.Coll. Nutr. 2000;19:220-7.
[xviii] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2418001/pdf/postmedj00127-0021.pdf
[xix] http://www.icmr.nic.in/ijmr/2008/march/0303.pdf
[xx] Hollick MF, Chen TC. Vitamin D deficiency a worldwide problem with health consequences. Am J Clin Nutr. 2008;87:10805–68.
[xxi] http://articles.mercola.com/sites/articles/archive/2009/10/29/how-much-sunshine-does-it-take-to-make-enough-vitamin-d-perhaps-more-than-you-think.aspx
[xxii] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3068797/
[xxiii] http://www.ncbi.nlm.nih.gov/pubmed/19663879
[xxiv] http://www.vitamindcouncil.org/news-archive/2009/showering-after-sunbathing/
[xxv]http://ajcn.nutrition.org/content/72/3/690.abstract?ijkey=b1ea181c3fb64e4a29fe2add84f34cda84066987&keytype2=tf_ipsecsha
[xxvi] http://jcem.endojournals.org/content/94/4/1214.long
[xxvii] http://www.grassrootshealth.net/daction#hqone
[xxviii] Heaney RP. Long-latency deficiency disease: insights from calcium and vitamin D. Am J Clin Nutr. 2003;78(5):912-9.
[xxix] Heaney RP. Long-latency deficiency disease: insights from calcium and vitamin D. Am J Clin Nutr. 2003;78(5):912-9.
[xxx] http://lifespa.com/2011/07/investigating-vitamin-d/
[xxxi] http://articles.mercola.com/sites/articles/archive/2006/11/11/can-a-tanning-bed-be-healthy.aspx
[xxxii] http://tanningbeds.mercola.com/tanning-beds/standup-tanning-systems.aspx
[xxxiii] http://www.mommypotamus.com/why-vitamin-d-supplements-cant-replace-sunshine/
[xxxiv] http://drbenkim.com/dr-michael-holick-vitamin-d.htm
[xxxv] http://renegadehealth.com/blog/2012/02/01/blood-tests-results-revealed

Gurjit Dhallu
London, England
Graduate of the School of Modern Naturopathy
August 2012