|Vitamin D Update: Diabetes, Cognitive Decline, Asthma, and Heart Attack
Vitamin D is continuing to make news. Although previously well-known for its effects on calcium absorption and therefore bone health, vitamin D has now 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 recent 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
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 In recent study in Italy, 25(OH)D levels and cognitive function were tested at baseline, and then follow-up cognitive tests were performed at three year intervals to quantify any decline in cognitive ability. This study found that the risk of significant cognitive decline was 60% higher in those who were deficient in vitamin D compared to those with sufficient levels.7 Although previous studies have been inconclusive8, this new data supports a role for vitamin D in maintaining brain health in older adults.
Two recent 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 are currently conducting 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
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 newly published 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.
1Hypponen E. Vitamin D and increasing incidence of type 1 diabetes-evidence for an association? Diabetes Obes Metab. 2010 Sep;12(9):737-43.
2University 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 http://www.sciencedaily.com /releases/2010/07/100715172042.htm
3Pittas 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.
4The Endocrine Society (2010, June 21). Poor control of diabetes may be linked to low vitamin D. ScienceDaily. Retrieved July 28, 2010, from http://www.sciencedaily.com /releases/2010/06/100621091209.htm
5Zipitis 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.
6McCann JC, Ames BN. Is there convincing biological or behavioral evidence
linking vitamin D deficiency to brain dysfunction? FASEB J. 2008
7Llewellyn 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.
8Annweiler 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.
9EurekAlert! Low vitamin D levels associated with more asthma symptoms and medication use. http://www.eurekalert.org/pub_releases/2010-04/njma-lvd041510.php#
Jancin B. Vitamin D Tied to Airway Hyperresponsiveness. Family Practice News. May 1, 2010.
10Sutherland 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.
11Brehm JM, Celedon 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.
12Litonjua AA. Childhood asthma may be a consequence of vitamin D deficiency. Curr Opin Allergy Clin Immunol. 2009 Jun;9(3):202-7.
12Washington University School of Medicine (2009, August 25). Why Low Vitamin D Raises Heart Disease Risks In Diabetics. ScienceDaily. Retrieved July 28, 2010, from http://www.sciencedaily.com /releases/2009/08/090821211007.htm
14Jancin B. CAD Events Less Likely With Normal Vitamin D. Family Practice News, May 15, 2010.