The Importance of Vitamin D
Vitamin D, the "sunshine vitamin," plays a major role in the development of bones and protects against muscle weakness. And its importance is growing, as new research has revealed that it prevents many health risks and diseases.
Doctors agree that to get enough vitamin D (at least by FDA standards), all you need is fifteen minutes of full sun exposure, without sunblock or cloud cover, twice a week. This sounds easy, and yet 75% of Americans are deficient in vitamin D,59 including 70% of children.58
Factors like living in the northern part of the country, having dark skin, or constantly using sunblock will affect how much vitamin D is produced by your body from sunlight. Moreover, excessive exposure to sunlight, particularly in young people, has been shown to increase skin cancer risk later in life. The alternative to this confusion is to obtain your vitamin D through food, an equally potent source.
But even so, the amount of vitamin D found in food is usually small - one glass of fortified milk contains 100 IU of vitamin D; one egg, 20 IU. By contrast, the Omega Cookie's content of 800IU can be a big help in ensuring that you always have the amount of vitamin D your body needs.
A lot of research has shown that vitamin D supplementation may go a long way in reducing the risk of developing diabetes.
Scientists at the University of California, San Diego, researched correlations between vitamin D and diabetes, analyzing national diabetes rates and comparing them with proximity to the equator (and therefore the extent of sun exposure). Even after controlling for confounding variables such as quality of health care, it was obvious that the sunny equatorial countries had lower diabetes rates. These results coincided with another study that found that in the study participants, vitamin D supplementation in infancy and early childhood reduced the risk of type 1 diabetes by 29%.8
Scientists from the Institute of Child Health in London conducted a birth-cohort study of 10,366. The 81 children who developed type 1 diabetes within a year had a lower vitamin D intake than the others, even after adjusting for other characteristics. Children who took vitamin D supplements (2,000 IU daily) appeared to be at the lowest risk of all for developing diabetes in the future.47
Des Moines University compared the vitamin D levels of 26 people with diabetes and 15 people without it. The people with diabetes, not too surprisingly, had significantly less vitamin D than their non-diabetic counterparts. "Given the importance of vitamin D in bone metabolism and the osseous consequences associated with diabetes, as well as other systems affected by low levels of vitamin D in the diabetic patient," the study's authors write, "it appears that vitamin D levels should be monitored in diabetic patients."48
Finland's National Public Health Institute pooled the data from two case-control cohort studies in which the vitamin D levels of a total 412 type 2 diabetics were compared with those of non-diabetics of similar age, health habits, etc. The results indicate that having more vitamin D seems to help protect against type 2 diabetes.49
Not only does vitamin D potentially reduce diabetes risk, it may make the condition more manageable for those who already have it.
The University hospital of Sofia, Bulgaria, conducted a case-controlled study of 27 females, 10 of whom had type 2 diabetes. As the diabetic women, over the course of one month of supplementation, reached the vitamin D levels of their non-diabetic counterparts, they also experienced improved insulin secretion and insulin sensitivity. The study's conclusion suggests that vitamin D may be a valuable part of type 2 diabetes treatment, especially during the winter when there is less sunlight exposure.50
An article review from Purdue University made a similar point: "Several clinical intervention studies [...] support that vitamin D [...] improves insulin sensitivity."51
And yet, even with all this positive science, one study found that, of the 28 type 1 diabetic youth studied, only 25% were not vitamin D deficient. Meanwhile, three-quarters were forfeiting a simple method of reducing the risk of several consequences of this disease.52
Doctors from Washington University School of Medicine performed lab tests in which they compared cholesterol uptake in diabetics and non-diabetics. They found that when the diabetics' vitamin D levels rose to equal those of their non-diabetic counterparts, ability to process cholesterol dramatically improved, cutting heart attack and stroke risk.62
The latest science is revealing that vitamin D may cut down on several cardiovascular risk factors, and therefore on the prevalence of heart disease and the frequency of cardiac events.
The Third National Health and Nutrition Examination Survey, conducted by the CDC (Centers for Disease Control), gathered information about 15,000 American adults over the age of 20. Among this population, a correlation existed between vitamin D deficiency and increased incidence of hypertension, diabetes, obesity, and high triglycerides, even after adjusting for other variables like age and race. All four of these conditions are, of course, major cardiovascular risk factors.37
A study out of Sweden also found an association between low vitamin D and high triglycerides and blood pressure, this time specifically in middle-aged men.38
A similar study comes from Uppsala, Sweden, where Gavle County Hospital carried out a prospective, placebo-controlled, double-blind study over the course of six months, in which vitamin D cause a "significant reduction" of diastolic blood pressure compared with placebo.43
Ruhr University Bochum in Germany conducted a review of previous experimental studies on the matter and concluded that vitamin D deficiency can contribute to hardening of the arteries. (Excessive vitamin D intake can have the same effect, but this is very rare in the modern Western world).39
Researchers at Marmara University School of Medicine in Istanbul, Turkey, studied arterial health in 23 vitamin D-deficient subjects who showed no symptoms, and reached the conclusion that "Vitamin D deficiency can be seen as an independent risk factor of atherosclerosis."60
A recent study published in the Journal of Inflammation found that vitamin D deficiency in women was associated with inflammation, a major contributing factor in heart disease, in addition to multiple sclerosis and rheumatoid arthritis.59
This risk reduction has notable consequences.
For instance, researchers from Austria observed the heart health of 3,258 patients (average age: 62) for over seven and a half years. By the study's end, the data suggested that "People with low blood levels of vitamin D are more than twice as likely to die from cardiovascular disease as those with high levels."5
Vigorous review from Chicago Medical School of previous randomized, placebo-controlled studies noted a "striking correlation" between low vitamin D levels and cardiovascular incidences like heart failure and heart attack.40
Several scientists from Harvard University and the Medical University of South Carolina prospectively assessed the correlation between vitamin D intake and heart attack (myocardial infarction) in 18,225 men ages 40 to 75 who were studied over the course of ten years in the Health Professionals Follow-up Study. The results showed that even after controlling for other risk factors known to be associated with coronary artery disease, risk of heart attack increased in inverse proportion with vitamin D levels.41
A community-based case-control study on the same topic, conducted by the University of Auckland in New Zealand, reached the same conclusion after studying 179 heart attack patients and comparing with corresponding control patients.42
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In a study of 3,316 patients conducted by the Synlab Center of Laboratory Diagnostics in Heidelberg, Germany, over the course of nearly eight years, researchers found a correlation between low vitamin D levels and increased stroke risk. The study speculates that these results imply that vitamin D supplementation could be one component of stroke prevention.10
Another study from Addenbrooke's Hospital in Cambridge, UK, also noted that "Vitamin D is a potential risk marker for stroke." The study's authors encouraged the conduction of further research on whether post-stroke vitamin D supplementation could improve muscular and skeletal health.11
In fact, one such study had already been conducted with a randomized, placebo-controlled design in Iizuka, Japan, on 96 elderly women who had had strokes. The group that received vitamin D, rather than a placebo, experienced less muscular atrophy, and subsequently fewer falls and hip fractures.12
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So far, the evidence associating vitamin D and cognitive function is not yet strong enough to confirm a causal relationship; however, the promising science that is currently available continues to spur ongoing investigation.
- In a study of 1,766 patients over the age of 65, researchers from Peninsula Medical School, the University of Cambridge, and the University of Michigan found that "compared to those with optimum levels of vitamin D, those with the lowest levels were more than twice as likely to be cognitively impaired."4 These findings suggest a correlation between vitamin D deficiency and risk of developing dementia later in life.
- Tufts University conducted cross-sectional investigation in which the vitamin D blood levels of 1,080 participants ages 68-99 were compared with their scores on a variety of neuropsychological assessments. While there was no correlation between vitamin D level and memory, those with more vitamin D in their blood did perform better on the cognitive tests.53
- The Health Survey for England 2000, a nationally representative population-based study, included data about 1766 adults aged 65 years and older. Among the 12% of these individuals who were cognitively impaired, blood vitamin D levels were significantly lower, implying some sort of connection.54
- A vitamin D receptor and related enzymes for vitamin D metabolism are located in the same part of the brain "involved in complex planning, processing, and the formation of new memories," so Tufts University has theorized that this may be more evidence that vitamin D and cognitive function are related.55
- A review of studies related to this potential connection was written by doctors from the Children's Hospital Oakland Research Institute in California. "We conclude there is ample biological evidence to suggest an important role for vitamin D in brain development and function," the article states, but adds the caveat that such a conclusion is tentative.56
- The University of Wisconsin-Madison analyzed the blood vitamin D levels and cognitive test scores of 32 patients and once again found a "positive, significant correlation" that "suggests a potential role for vitamin D in cognitive function of older adults."57
Research has indicated an association between vitamin D deficiency and cancer risk for years, but only recently have scientists come up with a potential explanation. It seems that when vitamin D is deficient (and particularly when vitamin D and calcium are deficient), cells lose the ability to communicate with one another. As a result, the regulation of the proper cycle of cell growth and death is disrupted among healthy cells, clearing the way for the more aggressive cancer cells to thrive and multiply. This association implies that eliminating vitamin D deficiency can prevent the growth of cancer in its early stages. Furthermore, over 200 real-word research studies have linked vitamin D to certain cancers, in addition to more than 2,500 laboratory studies.2 One recent study in particular found that upping vitamin D intake may reduce breast cancer risk by over 20%.6
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A Spanish study of 121 women of varying weights found an association between vitamin D deficiency and obesity.3 In 90 young women ages 16-22, higher vitamin D intake was associated with lower body fat and increased height.21 Four hundred ten healthy women between ages 20 and 80, studied by Winthrop-University Hospital in Mineola, New York, exhibited the same correlation between a high percentage of body fat and low vitamin D levels.24 In 60 morbidly obese women studied by the University of Tennessee, the data suggested "that low vitamin D may be associated with obesity per se [by itself]."25 The Veterans Administration Medical Center in Charleston, South Carolina, was yet another institution to point out that "vitamin D is significantly lower in obese than in nonobese individuals."22
More to the point, when researchers in Minnesota put 38 overweight men and women on a reduced-calorie diet, they found that the patients with more vitamin D in their blood lost more weight than the patients who were more deficient. The study's lead author, Shalamar Sibley, MD, from the University of Minnesota, commented, "Our results suggest the possibility that the addition of vitamin D to a reduced-calorie diet will lead to better weight loss."7 An article from Caterham on the Hill in Surrey, UK, concurred: "It may be possible to reverse the increasing prevalence of obesity by improving vitamin D status."20
Furthermore, a transversal, observational study out of Madrid, Spain, found a correlation between vitamin D deficiency and metabolic syndrome (commonly a precursor to diabetes) in its 73 morbidly obese participants.23
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Vitamin D can strengthen bones by increasing bone mineral density, fighting the bone softening and increased risk of fracture caused by osteoporosis.
Tufts University conducted a prospective observational study on 556 osteoarthritis patients, and found that low vitamin D intake and blood levels were associated with painful knee cartilage loss and risk for progression of the condition.44
In a cross-sectional, longitudinal study of 880 subjects (average age:61), the University of Tasmania also found that high vitamin D levels in the blood were associated with decreased knee cartilage loss.45
A third study from Boston University, with a population-based design observing 228 osteoarthritic subjects, found that bone mass density was better in those with higher vitamin D levels in their blood, a correlation that remained even after adjusting for variables like age and gender.26
Vitamin D plays an interesting role in the immune system, able to modulate it to reduce its response to a threat (to decrease inflammation) and increase its response (to fight off infection). The regulation is selective, and the role played by vitamin D (or a lack thereof) varies according to the amount of calcium available (more is better, of course) and "the nature of the immune response (eg, infectious disease, asthma, or autoimmune disease)," an article from Pennsylvania State University explains.29 However, a review of previous studies conducted by the Veterans Affairs Medical Center in San Francisco reached the conclusion that the net effect of vitamin D on the immune system is positive.30
- A study from Italy found that vitamin D was capable of enhancing both innate (generic) and adaptive (target-specific) immunity, due to the fact that the vitamin's effects vary: it can be antibacterial, anti-inflammatory and immunomodulatory, among other things. The study went on to comment, "Epidemiological [from the real world, not a laboratory] evidence indicates a significant association between vitamin D deficiency and an increased incidence of several autoimmune diseases." This helps explain why vitamin D seems to be able to ward off rheumatoid arthritis and type 1 diabetes, and suggests that in the future, we may find out that it affects lupus, multiple sclerosis, and other conditions, too.31
An interventional study from Atascadero State Hospital in California also found that among the children who participated, vitamin D reduced the frequency of respiratory infections, including the flu.32
Many of the studies currently available focus on vitamin D's effects on tuberculosis protection.
- A meta-analysis of seven previous studies out of Oxford, England, concluded that low levels of vitamin D in the blood seem to increase the likelihood of contracting active tuberculosis.33
- Royal Melbourne Hospital found the same correlation in African immigrants to Australia.34
- And in an experiment conducted by Northwick Park Hospital in the UK, a single dose of 2.5 mg vitamin D (which, given, is a massive amount) significantly enhanced the bodies ability to fight off mycobacteria, which cause tuberculosis.35
The effects on vitamin D on the immune system are serious. The Sunlight, Nutrition, and Health Research Center in San Francisco estimated that if everyone in western Europe upped his or her vitamin D intake to 2,000 to 3,000 IU, it would cost €10 billion annually, but it would save €187 billion annually in health care costs.36
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The University of Oslo in Norway conducted a study in which 48 women took fish oil throughout their pregnancy and for the first three months of breastfeeding, whereas 36 women took a placebo (corn oil). They found that the average IQ at age four of children born to the fish oil group significantly exceeded that of the placebo group.61 back to top
The fact that diabetes rates in America first began to increase in the 1960s, when people were spending less time outdoors and probably receiving less vitamin D, has aroused interest in a possible connection. So far the research on the topic is limited, but intriguing.
In the studies they conducted, scientists at Brigham and Women's Hospital in Boston found that "higher vitamin D intake by pregnant mothers reduces asthma risk by as much as 40% in children 3 to 5 years old."27
In the 616 asthmatic Costa Rican children studied by Channing Laboratory, rates of vitamin D deficiency were unusually high given the country's close proximity to the equator (and hence high exposure to direct sunlight). Furthermore, there was a positive association between the severity of the vitamin D deficiency and the number of asthma-related hospitalizations in the previous year, indicative of the severity of the condition.28
Another study from the University of California, San Diego, was conducted on 14 people with ectopic dermatitis and 14 people with normal skin. The results implied that in both sets of patients, vitamin D helped boost production of protective compounds in the skin, with the potential effect of improved prevention of skin infections.9
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The Queensland Centre for Schizophrenia Research in Australia found that rats born to mothers with vitamin D deficiencies had brains that were physically deformed and proceeded to develop abnormally, so evidence that vitamin D seems to play a role in mood isn't too surprising.13 In fact, a review of previous studies written by scientists from the Medical University of South Carolina found that in women, vitamin D deficiency was associated with "premenstrual syndrome, seasonal affective disorder, non-specified mood disorder, and major depressive disorder."14
The University of Tromso in Norway conducted a randomized, double-blind, placebo-controlled trial on 441 subjects who were depressed and either overweight or obese. The researchers found an inverse correlation between vitamin D levels and severity of depressive symptoms.15
In a longitudinal study of 80 elderly participants, the Washington University School of Medicine also found an association between vitamin D deficiency and low mood.16
An article written by scientists at the University of Miami noted the same correlation, in addition to connections to bipolar disorder and schizophrenia.17
Some researchers have chosen to particularly focus on vitamin D's role in the prevention of Seasonal Affective Disorder (SAD), a seasonal depression that worsens during the winter months.
The University of Newcastle in Australia conducted a controlled study of 44 participants in late winter. After five days, the subjects reported that they were experiencing "significantly enhanced positive affect," and "there was some evidence of a reduction in negative affect."18
A prospective, randomized controlled trial conducted in a group of 15 subjects with SAD by Union Memorial Hospital in Baltimore also found that "All subjects receiving vitamin D improved in all outcome measures," suggesting that "Vitamin D may be an important treatment for SAD."19
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The research on vitamin D and autism is scant, but interesting. An article written by a doctor at Atascadero State Hospital in California sums up the notable points.
The rise in autism rates corresponds to the decreased exposure to the sun (and hence lower vitamin D) that began about twenty years ago, when the dangers of ultraviolet radiation became known.46
In experiments, rats who were severely vitamin D deficient in gestation shared some of the same abnormal hallmarks of physical brain development exhibited by autistic children.
"Children with vitamin D deficient rickets have several autistic markers that apparently disappear with high-dose vitamin D treatment."
Estrogen and testosterone have different effects on the body's metabolism of vitamin D, which might explain the disproportionate gender ratio of people with autism.
Autism is more common in areas further from the equator, which receive less direct sunlight.
Autism is also more common in people with dark skin, who are also at a higher risk for vitamin D deficiency.
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The FDA recommends a vitamin D intake of 200 International Units daily, but virtually all doctors agree that the suggestion is outdated. A commonly recommended daily intake is 1,000 IU, though some scientists have gone so far as to push for raising the requirement to 2,000 IU.1 However, be careful to not take in too much vitamin D. In particular, young children should not receive more than 400 IU daily, and adults probably should not receive much more than 2,000 IU.4
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1. NutraIngredients-USA.com: "'Call to action' issued for raising vitamin D levels." 18 November 2008.
2. ScienceDaily: "New Model Of Cancer Development: Low Vitamin D Levels May Have Role." 26 May 2009.
3. The Journal of Endocrinological Investigation: "Low 25-hydroxyvitamin D concentrations in obese women: their clinical significance and relationship with anthropometric and body composition variables." September 2007.
4. NutraIngredients-USA.com: "Low vitamin D linked to higher risk of dementia: Study." 23 January 2009.
5. NutraIngredients-USA.com: "More vitamin D for fewer heart-related deaths: study." 24 June 2008.
6. NutraIngredients-USA.com: "Vitamin D again linked to breast cancer protection." 26 September 2008.
7. NutraIngredients-USA.com: "Vitamin D linked to successful weight loss with dieting." 12 June 2009.
8. CBS News: "Vitamin D May Cut Risk Of Type 1 Diabetes." 2008.
9. NutraIngredients-USA.com: "Vitamin D may protect skin from within: Study." 8 October 2008.
10. Stroke: "Low vitamin d levels predict stroke in patients referred to coronary angiography." September 2008.
11. Stroke: "Reduced vitamin D in acute stroke." January 2006.
12. Cerebrovascular Diseases: "Low-dose vitamin D prevents muscular atrophy and reduces falls and hip fractures in women after stroke: a randomized controlled trial." 27 July 2005.
13. Neuroscience: "Vitamin D3 and brain development." 2003.
14. The Journal of Midwifery & Women's Health: "Vitamin D and mood disorders among women: an integrative review." October 2008.
15. The Journal of Internal Medicine: "Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial." December 2008.
16. The American Journal of Geriatric Psychiatry: "Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults." December 2006.
17. Current Psychiatry Reports: "Some new food for thought: the role of vitamin D in the mental health of older adults." February 2009.
18. Pyschopharmacology: "Vitamin D3 enhances mood in healthy subjects during winter." February 1998.
19. The Journal of Nutrition, Health & Aging: "Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder." 1999.
20. Medical Hypotheses: "Vitamin D deficiency is the cause of common obesity." March 2009.
21. The Journal of Clinical Endocrinology and Metabolism: "Vitamin D status and its relationship to body fat, final height, and peak bone mass in young women." January 2009.
22. Calcified Tissue International: "Low circulating vitamin D in obesity." October 1998.
23. Clinical Nutrition (Edinburgh, Scotland): "Vitamin D deficiency is associated with the metabolic syndrome in morbid obesity." October 2007.
24. The Journal of Clinical Endocrinology and Metabolism: "Body fat content and 25-hydroxyvitamin D levels in healthy women." January 2003.
25. Obesity Surgery: "Vitamin D Deficiency in the Morbidly Obese." November 1993.
26. Arthritis and Rheumatism: "Positive association between serum 25-hydroxyvitamin D level and bone density in osteoarthritis." 15 December 2005.
27. The Journal of Allergy and Clinical Immunology: "Is vitamin D deficiency to blame for the asthma epidemic?" November 2007.
28. The American Journal of Respiratory and Clinical Care Medicine: "Serum vitamin D levels and markers of severity of childhood asthma in Costa Rica." 1 May 2009.
29. The American Journal of Clinical Nutrition: "Vitamin D status, 1,25-dihydroxyvitamin D3, and the immune system." December 2004.
30. Current Opinion in Nephrology and Hypertension: "Vitamin D and the immune system: role in protection against bacterial infection." July 2008.
31. Natural Clinical Practice. Rheumatology: "Control of autoimmune diseases by the vitamin D endocrine system." August 2008.
32. Epidemiology and Infection: "Epidemic influenza and vitamin D." December 2006.
33. The International Journal of Epidemiology: "Low serum vitamin D levels and tuberculosis: a systematic review and meta-analysis." February 2008.
34. Clinical Infectious Diseases: "Vitamin D deficiency is associated with tuberculosis and latent tuberculosis infection in immigrants from sub-Saharan Africa." February 2008.
35. The American Journal of Respiratory and Clinical Care Medicine: "A single dose of vitamin D enhances immunity to mycobacteria." 15 July 2007.
36. Progress in Biophysics and Molecular Biology: "Estimated benefit of increased vitamin D status in reducing the economic burden of disease in western Europe." 4 March 2009.
37. The Archives of Internal Medicine: "Prevalence of Cardiovascular Risk Factors and the Serum Levels of 25-Hydroxyvitamin D in the United States." 11 June 2007.
38. The American Journal of Hypertension: "Vitamin D is related to blood pressure and other cardiovascular risk factors in middle-aged men." 3 April 1995.
39. Current Opinion in Lipidology: "Vitamin D and vascular calcification." February 2007.
40. The American Journal of Therapeutics: "Vitamin D Deficiency and Its Correlations With Increased Cardiovascular Incidences." 15 May 2009.
41. The Archives of Internal Medicine: "25-Hydroxyvitamin D and Risk of Myocardial Infarction in Men." 9 June 2008.
42. The International Journal of Epidemiology: "Myocardial infarction is inversely associated with plasma 25-hydroxyvitamin D3 levels: a community-based study." September 1990.
43. The American Journal of Hypertension: "Hypertension in primary hyperparathyroidism-reduction of blood pressure by long-term treatment with vitamin D (alphacalcidol). A double-blind, placebo-controlled study." October 1988.
44. Annals of Internal Medicine: "Relation of dietary intake and serum levels of vitamin D to progression of osteoarthritis of the knee among participants in the Framingham Study." 1 September 1996.
45. Arthritis and Rheumatism: "Serum levels of vitamin D, sunlight exposure, and knee cartilage loss in older adults: the Tasmanian older adult cohort study." May 2009.
46. Medical Hypotheses: "Autism and vitamin D." 2008.
47. Lancet: "Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study." 3 November 2001.
48. The Journal of the American Podiatric Medical Association: "A comparison of vitamin D levels in nondiabetic and diabetic patient populations." February 2009.
49. Epidemiology: "Serum vitamin D and subsequent occurrence of type 2 diabetes." September 2008.
50. The International Journal of Clinical Practice: "The effect of vitamin D3 on insulin secretion and peripheral insulin sensitivity in type 2 diabetic patients." May 2003.
51. Nutrition Research Reviews: "Vitamin D: emerging new roles in insulin sensitivity." June 2009.
52. The Journal of Pediatrics: "Significant Vitamin D Deficiency in Youth with Type 1 Diabetes Mellitus." January 2009.
53. The Journals of Gerontology: "Vitamin D is associated with cognitive function in elders receiving home health services." August 2009.
54. The Journal of Geriatric Psychiatry and Neurology: "Serum 25-Hydroxyvitamin D Concentration and Cognitive Impairment." 4 Feb 2009.
55. Molecular Aspects of Medicine: "Vitamin D and neurocognitive dysfunction: preventing D'ecline?" December 2008.
56. The Journal of the Federation of American Societies for Experimental Biology: "Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction?" April 2008.
57. Archives of Biochemistry and Biophysics: "Is vitamin D important for preserving cognition? A positive correlation of serum 25-hydroxyvitamin D concentration with cognitive function." 15 April 2007.
58. CNN: "Vitamin D deficiency common in U.S. children." 3 August 2009.
59. Medical News Today: "Relationship Between Vitamin D Deficiency And Increased Inflammation In Healthy Women." 9 April 2009.
60. The Journal of Clinical Endocrinology and Metabolism: "Effect of vitamin D deficiency and replacement on endothelial function in asymptomatic subjects." 7 July 2009.
62. NutraIngredients-USA.com: "Study identifies vitamin D's benefits for diabetic heart health." 24 August 2009.
For a larger collection of Vitamin D research, visit the website of the Vitamin D Council.