Vitamin D update: Diabetes, cognitive decline, asthma, and heart attack

Vitamin D continues to make news.  Although previously well-known for its effects on calcium absorption and therefore bone health, vitamin D has also emerged as a contributor to many nonskeletal physiological processes, and functions have been attributed to vitamin D in the prevention of cancer, cardiovascular disease, infections, autoimmune diseases, and more. There are vitamin D receptors in almost every cell in the human body, and vitamin D regulates the expression of over 200 different genes. It is not surprising that sufficient vitamin D is crucial to the proper function of so many of our body’s tissues.1

Scientists estimate that 50% of the population of North America and Western Europe has insufficient blood vitamin D levels (as measured by 25(OH)D; sufficient is defined as greater than 30 ng/ml). Although recommended vitamin D intakes remain at only 200-400 IU per day, there is consensus among the scientific community that 2000 IU or more may be necessary for most  people to maintain sufficient blood levels.2

The newest research has found that vitamin D sufficiency is important for preventing type 2 diabetes, cognitive decline, asthma, and cardiovascular disease.




Type 2 diabetes

There is some evidence that vitamin D is involved in insulin secretion by pancreatic beta cells, since insulin secretion is a calcium-dependent process. Vitamin D may also prevent the development of insulin resistance by stimulating expression of the insulin receptor on the surface of cells that use glucose as fuel.3 A study performed at Johns Hopkins University School of Medicine on type 2 diabetics found that 91% of the patients were either deficient (less than 15 ng/ml) or insufficient (between 15 and 30 ng/ml) in vitamin D. Furthermore, there was inverse association between vitamin D levels and HbA1c, an indicator of blood glucose levels over the preceding 2-3 months, implying that vitamin D sufficiency contributes to glycemic control in diabetics.4 Vitamin D’s effects are not specific to type 2 diabetes; there is also convincing evidence that vitamin D supplementation during pregnancy and early childhood can reduce the risk of type 1 diabetes, and prospective studies on this topic are ongoing.1,5

Cognitive decline

Vitamin D receptors are present throughout the entire human brain, and genes that are regulated by vitamin D are involved in processes such as memory formation and neurotransmission.6,7 Although previous studies have been inconclusive8, this data supports a role for vitamin D in maintaining brain health in older adults. 


Two studies on asthma, one in adults and one in children, has linked vitamin D insufficiency with increased asthma severity.9 Those with 25(OH)D levels above 30 ng/ml had greater lung function, and used less medication.10 A similar study in children also found that lower vitamin D levels were associated with increased asthma severity, and that higher vitamin D levels were associated with reduced odds of hospitalization for asthma.11 Vitamin D’s anti-inflammatory actions or regulation of smooth muscle cell contraction via calcium handling may be the responsible factors. The researchers also conducted a trial investigating vitamin D supplementation as a therapeutic option for asthma. Vitamin D is also important for lung development in utero, so maternal supplementation with vitamin D during pregnancy is recommended.12

Cardiovascular disease

There is continually building evidence in the literature that sufficient vitamin D levels protect against cardiovascular disease. Vitamin D deficiency is extremely prevalent among heart attack sufferers – 96% of heart attack sufferers in a recent study were either insufficient (21%) or deficient (75%) in vitamin D. Those with sufficient vitamin D levels are less likely to die from heart attack or stroke.  Vitamin D insufficiency may allow for increased cholesterol uptake by inflammatory cells, which contributes to atherosclerosis.13 A study recorded vitamin D levels at baseline and throughout 6 years of follow-up. At the start of the study, the average 25(OH)D level was 19.3 ng/ml (insufficient). During the trial, about half of the subjects increased their levels to the sufficient range (above 30 ng/ml), and these subjects had significantly reduced incidence of heart attack, heart failure, and coronary artery disease. Some subjects raised their 25(OH)D levels above 44 ng/ml, and they received even stronger protection against cardiovascular disease. Compared to those who reached levels above 44 ng/ml, those whose levels stayed between 10 and 19 ng/ml had a 27% increase in coronary artery disease, a 32% increase in heart failure, and a 59% increase in heart attack incidence.14

Maintaining sufficient vitamin D levels is essential to our health. 

Very few foods naturally contain vitamin D and we cannot rely on sun exposure alone because of indoor jobs, cool climates, and the risk of skin cancer that may arise from adequate amounts of sun exposure to maintain vitamin D levels.   Plus, requirements vary with genetics and skin type greatly effecting Vitamin D production in the skin.  Taking a multivitamin is not the answer because almost all  multivitamins still provide an inadequate amount of vitamin D (400 IU). Favorable levels can be confirmed with a blood test, and supplementation can be adjusted accordingly.   I recommend supplementing with an adequate amount of vitamin D in order to maintain 25(OH)D levels of 35-55 ng/ml. For some people 2000 IU will be sufficient, but others may require more.


1. Hyppönen E. Vitamin D and increasing incidence of type 1 diabetes-evidence for an association? Diabetes Obes Metab. 2010 Sep;12(9):737-43.

2. University of California - Riverside (2010, July 19). More than half the world's population gets insufficient vitamin D, says biochemist. ScienceDaily. Retrieved July 28, 2010, from /releases/2010/07/100715172042.htm

3. Pittas AG, Lau J, Hu FB, Dawson-Hughes B. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. J Clin Endocrinol Metab. 2007 Jun;92(6):2017-29.

4. The Endocrine Society (2010, June 21). Poor control of diabetes may be linked to low vitamin D. ScienceDaily. Retrieved July 28, 2010, from /releases/2010/06/100621091209.htm

5. Zipitis CS, Akobeng AK. Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and meta-analysis. Arch Dis Child. 2008 Jun;93(6):512-7.

6. McCann JC, Ames BN. Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction? FASEB J. 2008 Apr;22(4):982-1001.

7. Llewellyn DJ, Lang IA, Langa KM, et al. Vitamin D and Risk of Cognitive Decline in Elderly Persons Arch Intern Med. 2010;170(13):1135-1141.

8. Annweiler C, Allali G, Allain P, et al. Vitamin D and cognitive performance in adults: a systematic review. Eur J Neurol. 2009 Oct;16(10):1083-9.

9. EurekAlert! Low vitamin D levels associated with more asthma symptoms and medication use.

Jancin B. Vitamin D Tied to Airway Hyperresponsiveness. Family Practice News. May 1, 2010.

10. Sutherland ER, Goleva E, Jackson LP, et al. Vitamin D levels, lung function, and steroid response in adult asthma. Am J Respir Crit Care Med. 2010 Apr 1;181(7):699-704.

11. Brehm JM, Celedón JC, Soto-Quiros ME, et al. Serum vitamin D levels and markers of severity of childhood asthma in Costa Rica. Am J Respir Crit Care Med. 2009 May 1;179(9):765-71.

12. Litonjua AA. Childhood asthma may be a consequence of vitamin D deficiency. Curr Opin Allergy Clin Immunol. 2009 Jun;9(3):202-7.

13. Washington University School of Medicine (2009, August 25). Why Low Vitamin D Raises Heart Disease Risks In Diabetics. ScienceDaily. Retrieved July 28, 2010, from /releases/2009/08/090821211007.htm

14. Jancin B. CAD Events Less Likely With Normal Vitamin D. Family Practice News, May 15, 2010.


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Comments (10) Read through and enter the discussion with the form at the end
Tally - August 3, 2010 4:09 PM

The July/August 2010 issue of Nutrition Action Healthletter (Center for Science in the Public Interest) reported studies in which those with the highest blood levels of Vitamin D (40 ng/mL or more) were approximately twice as likely to be diagnosed with pancreatic cancer as those with lower levels. They recommend keeping levels around 30 ng/mL (700-1000 IU/day) until more studies are completed.
Since I respect you both, it's hard to know what to believe on this subject. Thank you for any clarification.

Beth - August 3, 2010 8:23 PM

@Tally, the Vitamin D Council discusses this (I know, they're obviously in favor of Vitamin D!) here:

I also would be very interested in a clarification on this! Thank you.

Deana Ferreri, Ph.D. - August 4, 2010 10:49 AM

Tally and Beth,

As mentioned in the research paper from the American Journal of Epidemiology reported on by CSPI, statistically significant reductions in risk of colorectal cancer have been found with increasing 25(OH)D. There is also some evidence that vitamin D may be protective against breast, prostate, and endometrial cancers (more info here: #library/vitamin_D_the_right_stuff.aspx).
The paper in the American Journal of Epidemiology analyzed studies on rarer cancer sites, and did find an increase in risk for pancreatic cancer for subjects with 25(OH)D greater than 40ng/ml (no effect was found for the other sites investigated.) Please note that in the study that contributed the largest number of pancreatic cancer cases to this study (which found increased risk only above 65ng/ml 25(OH)D), all of the subjects were smokers, and increasing 25(OH)D levels were associated with serum retinol (vitamin A) and fish intake (not vitamin D supplementation). The authors note that contaminants found in vitamin D-rich fish have been associated with pancreatic cancer. The bottom line is that the association and the reasons for it are not very clear, and there are factors other than vitamin D itself to be considered.

Beth - August 4, 2010 3:30 PM

So, is the risk then associated only with retinol/vitamin D-rich fish? (And smoking, of course?)

I'm asking because I was taking Vitamin D to prevent flu during pregnancy, and my level went from 38-62. I still occasionally take 1000IU (when I haven't had much sun in a while). There is pancreatic cancer in my family (though, both family members smoked). (There is also breast cancer in the family; it would be incongruous and unfair that a hormone/vitamin could protect against some cancers/diseases, and make one more susceptible to others!)

Deana Ferreri, Ph.D. - August 4, 2010 5:16 PM

It's not clear yet based on the research done so far - we cannot be sure whether the vitamin D, vitamin A, contaminants in fish, or some other factor was the cause of the increased pancreatic cancer risk. Vitamin D seems unlikely, since it seems to have a protective effect against other cancers.

Thomas Johnson - August 6, 2010 1:33 PM

Earlier this year Dr. John McDougall referenced "a landmark editorial published in the March 2, 2010 issue of the Annals of Internal Medicine which concluded ..that the evidence for widespread use of high-dose vitamin D supplementation in the general population remains insufficient." Dr. McDougall's analysis of this and the recent literature on Vitamin D led him to conclude that "Vitamin D Pills Are of Little or No Benefit and Some Harm. So What do we Do Now?" See www, for more details. Could you comment on the validity of this advice and this conclusion? Thank you!

Michael - August 6, 2010 3:35 PM

I can only speak from personal experience, but supplementing with Vitamin D has helped me tremendously as far as reducing fatigue and improved my resistance to sinus infections. As far as getting Vitamin D from the sun, I haven't had much luck increasing my levels with that method. They make it sound like a few minutes a day is all you need but I regularly exercised outside cycling and walking in Atlanta and devloped a deficiency. I am light-skinned and have Scottish ancestry, so I think if it were really so easy, I wouldn't have had a problem.

Deana Ferreri, Ph.D. - August 10, 2010 9:02 AM


Dr. Fuhrman thoroughly addresses these issues in his newsletter on Vitamin D (available to his members) but essentially current evidence at this time does not support the view espoused-- that most people should eschew supplements and struggle to achieve Vitamin D adequacy with sunshine or sunlamps, under some theory that skin-derived Vitamin D is superior to oral consumed via supplements.

In our current world, sufficient sun exposure is only available to a small percentage of the population and a safe amount of sun exposure is simply not adequate for many people to maintain sufficient vitamin D levels. Studies on individuals with high sun exposure still report a high prevalence of vitamin D insufficiency. A study of young adults in Honolulu, Hawaii who averaged 22 hours of unprotected sun exposure per week found that 51% of these subjects had insufficient blood vitamin D levels (reference below). Tanning beds are a concentrated source of UV radiation known to increase skin cancer risk.

Furthermore there is no solid evidence that vitamin D supplementation has been associated with a host of adverse effects as claimed, and scaring people against Vitamin D supplementation could result in significant pathology, including cancer. There is no controversy here. Observational studies have made it clear that vitamin D insufficiency is associated with risk for a great number of disease states. A sufficient blood level of vitamin D has been established by scientists, and there is no reason for anyone to remain deficient. The high prevalence of vitamin D insufficiency and deficiency in heart attack sufferers and the association between deficiency and death from heart attack and stroke cannot be ignored.

A few hand-picked studies with flaws (one comparing D supplement to hormones) and those that use exceptionally (dangerously) high levels of supplemental D do not make a legitimate argument against supplementing appropriately to assure level are in the ideal range.

Before deciding whether sun exposure can provide you with enough vitamin D, get a blood test. This will tell you whether you need to supplement – most people do. The biggest problem will arise if a person thinks they do not need to get their blood tested, assuming that the sun they get is sufficient and unknowingly remain Vitamin D deficient. We see this all the time in Dr. Fuhrman’s office.

Finally, McDougall correctly states that vitamin D toxicity is known only to occur in those who take 10,000 IU or more daily for an extended period of time. Dr. Fuhrman recommends approximately 2000 IU for most people, and that supplementation be guided by blood 25(OH)D levels. In light of recent research, the Institute of Medicine is in the process of reevaluating its recommendations, and will likely raise the tolerable upper limit. Current scientific consensus tells us that 2000 IU is safe for most people, and that vitamin D sufficiency is essential for our health.

Binkley N, Novotny R, Krueger D, et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007 Jun;92(6):2130-5.

StephenMarkTurner - August 10, 2010 12:21 PM

Over the years it seems Dr John McDougall has believed that most nutrients that are often found in animal foods are unnecessary for humans in anything but small amounts. Examples are protein, zinc, vitamin B12, long chain w3 fats, and vitamin D.

I am certainly not qualified to rebut Dr McD, but I can't help but get the feeling that he starts with the axiom that a starchy vegan diet is perfectly healthy, and makes all his conclusions from there.

Regards, Steve

Andy @ diabetic tips - September 14, 2010 3:22 AM

Really interesting information. The whole issue with vitamin D has been talked about for some time. It does need to be looked at from different sources though. Otherwise the information can be biased.

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