D Is for Diabetes
Low vitamin D levels linked to increased risk of disease
By A. Paul Chous, MA, OD, FAAO
Vitamin D regulates levels of calcium and phosphorus necessary for the strength and growth of bones. In addition, it influences the expression of many genes that influence health and disease. A variety of evidence is accumulating that shows a majority of Americans have low vitamin D levels and that this may increase our risk of several serious medical conditions, including cancer, cardiovascular disease, multiple sclerosis, and diabetes. Here, I'd like to explain a bit of the science behind vitamin D, particularly as it relates to the risk of developing both type 1 diabetes and type 2 diabetes, as well as serious diabetes-related complications, including eye disease.
Vitamin D acts like a hormone at the cellular level, decreasing production of inflammatory proteins while increasing anti-inflammatory proteins, regulating immune system function, lowering blood pressure, improving insulin sensitivity, and preventing the deposition of calcium that makes up the majority of atherosclerotic plaques within our arteries. Therefore, it is not surprising that low vitamin D levels are associated with inflammatory, autoimmune diseases (e.g. type 1 diabetes and multiple sclerosis), high blood pressure, insulin resistance and type 2 diabetes , and cardiovascular disease like heart attack and stroke. Even more striking is the link between several types of cancer (especially breast and colon) and low vitamin D levels; one epidemiologic study suggests that every 10 ng/ml increase in blood levels of vitamin D reduces the risk of all cancers by 35% (see figure below, reprinted with permission by GrassrootsHealth.)
Humans are able to synthesize vitamin D when our skin is exposed to sunlight, specifically ultraviolet B radiation (UVB). Once exposed to UVB, precursors to vitamin D stored in our skin are released into the blood stream where they are converted by the liver and kidneys into biologically active forms that regulate a number of metabolic processes within our bodies' cells. About 90% of our blood concentrations of active vitamin D are derived from sun exposure, with the balance coming from dietary sources; In fact, the incidence of type 1 diabetes has been shown to increase the farther people live from the equator with decreasing UVB exposure and vitamin D levels. Similarly, people who work indoors, wear clothing that covers up exposed skin, and/or consume diets with inadequate levels of vitamin D are at higher risk for deficiency.
All percentages reference a common baseline of 25 ng/ml as shown on the chart. %'s reflect the disease prevention % at the beginning and ending of available data. Example: Breast cancer incidence is reduced by 30% when the serum level is 34 ng/ml vs the baseline of 25 ng/ml. There is an 83% reduction in incidence when the serum level is 50 ng/ml vs the baseline of 25 ng/ml. The x's in the bars indicate ‘reasonable extrapolations' from the data but are beyond existing data.
All Cancers: Lappe JM, et al. Am J Clin Nutr. 2007;85:1586-91. Breast: Garland CF, Gorham ED, Mohr SB, Grant WB, Garland FC. Breast cancer risk according to serum 25-Hydroxyvitamin D: Meta-analysis of Dose-Response (abstract).American Association for Cancer Research Annual Meeting, 2008. Reference serum 25(OH)D was 5 ng/ml. Garland, CF, et al. Amer Assoc Cancer Research Annual Mtg, April 2008,. Colon: Gorham ED, et al. Am J Prev Med. 2007;32:210-6. Diabetes: Hyppnen E, et al. Lancet 2001;358:1500-3. Endometrium: Mohr SB, et al. Prev Med. 2007;45:323-4. Falls: Broe KE, et al. J Am Geriatr Soc. 2007;55:234-9. Fractures: Bischoff-Ferrari HA, et al. JAMA. 2005;293:2257-64. Heart Attack: Giovannucci et al. Arch Intern Med/Vol 168 (No 11) June 9, 2008. Multiple Sclerosis: Munger KL, et al. JAMA. 2006;296:2832-8. Non-Hodgkin's Lymphoma: Purdue MP, et al. Cancer Causes Control. 2007;18:989-99. Ovary: Tworoger SS, et al. Cancer Epidemiol Biomarkers Prev. 2007;16:783-8. Renal: Mohr SB, et al. Int J Cancer. 2006;119:2705-9. Rickets: Arnaud SB, Copyright GrassrootsHealth, 10/16/08 www.grassrootshealth.org.
D-action, a consortium of researchers and physicians concerned about the health effects of widespread vitamin D deficiency in our country, recommends blood levels of 25-hyxdroxyvitamin D (the biologically active form) between 40 and 60 nanograms per milliliter (ng/ml). Research shows an average vitamin D level in the U.S. population of 30 ng/ml, with up to 70% of people having levels below 30 ng/ml and even lower levels in women, the elderly, overweight and obese persons, patients with kidney disease, and those with diabetes. It is particularly important, I believe, to note the association between diabetes and cancer, cardiovascular disease, Alzheimer's disease, and other conditions with respect to underlying low levels of vitamin D; whether or not low D levels cause or contribute to these disorders, or are merely a marker for them remains an open question, but the scientific evidence is compelling. In terms of eye disease, vitamin D deficiency appears to be associated with both an increased risk of diabetic retinopathy and age-related macular degeneration, two of the leading causes of permanent vision loss in the US.
As mentioned already, the primary source of vitamin D is sunlight exposure on bare skin (without sun screen), especially during hours of peak UVB radiation (11 AM – 1 PM); a mere 15-20 minutes of exposure during summer months generates up to 10,000 IU of 25-hydroxyvitamin D, which can be stored in the liver for future use. It is important to note that people with darkly pigmented skin require more sun exposure (up to 10 times more) to achieve the same effect. For people living in environments with less sun exposure, dietary or supplemental vitamin D may be extremely important. Foods rich in vitamin D include cold water, fatty fish, soy beans, eggs, and fortified milk. Unfortunately, milk is typically fortified with vitamin D2, a biologically less active form. In addition, 90% of African-Americans are lactose intolerant, making milk consumption impractical for achieving adequate levels of vitamin D in this population.
Vitamin D3 supplements are a very inexpensive way to achieve adequate blood concentrations of 25-hydroxyvitamin D. Many scientists now recommend a minimum of 1000-2000 IU of vitamin D3 per day for adults, with higher dosages for people of color, those living in the Northern U.S., people who spend most daylight hours indoors, the elderly, and those with deficiency proven by laboratory testing. Anecdotally, I have consistently found low vitamin D levels in my patients with diabetes, and somewhat lower levels in my patients with diabetic retinopathy. Typically, every 1000 IU increase in vitamin D3 will raise blood levels about 10 ng/ml over several months. People with diabetes who are concerned about their vitamin D status – and every one of us should be – can request an inexpensive blood test from their physicians or go to www.grassrootshealth.org to order a simple, at-home blood test to determine their levels and check the effectiveness of any supplement regimen. Their website is also full of great information on vitamin D and health, including a terrific video presentation on prevention of (type 1) diabetes.
For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
Read more about Dr. Chous here.
Visit Dr. Chous' website here.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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