A study led by researchers from the University of California, San Diego School of Medicine has found a correlation between vitamin D3 serum levels and subsequent incidence of Type 1 diabetes. The six-year study of blood levels of nearly 2,000 individuals suggests a preventive role for vitamin D3 in this disease. The research appears the December issue of Diabetologia, a publication of the European Association for the Study of Diabetes (EASD).
"Previous studies proposed the existence of an association between vitamin D deficiency and risk of and Type 1 diabetes, but this is the first time that the theory has been tested in a way that provides the dose-response relationship," said Cedric Garland, DrPH, FACE, professor in UCSD's Department of Family and Preventive Medicine.
This study used samples from millions of blood serum specimens frozen by the Department of Defense Serum Registry for disease surveillance. The researchers thawed and analyzed 1000 samples of serum from healthy people who later developed type 1 diabetes and 1000 healthy controls whose blood was drawn on or near the same date but who did not develop type 1 diabetes. By comparing the serum concentrations of the predominant circulating form of vitamin D - 25-hydroxyvitamin D (25(OH)D) - investigators were able to determine the optimal serum level needed to lower an individual's risk of developing type 1 diabetes.
Based mainly on results of this study, Garland estimates that the level of 25(OH)D needed to prevent half the cases of type 1 diabetes is 50 ng/ml. A consensus of all available data indicates no known risk associated with this dosage.
"While there are a few conditions that influence vitamin D metabolism, for most people, 4000 IU per day of vitamin D3 will be needed to achieve the effective levels," Garland suggested. He urges interested patients to ask their health care provider to measure their serum 25(OH)D before increasing vitamin D3 intake.
"This beneficial effect is present at these intakes only for vitamin D3," cautioned Garland. "Reliance should not be placed on different forms of vitamin D and mega doses should be avoided, as most of the benefits for prevention of disease are for doses less than 10,000 IU/day."
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Link Between Vitamin D Deficiency And Type 1 Diabetes
Increased Risk For Diabetes When Obesity And Low Vitamin D Are Present
"Vitamin D insufficiency and obesity are individual risk factors for insulin resistance and diabetes," said lead author Shaum Kabadi, a doctoral candidate in epidemiology at Drexel. "Our results suggest that the combination of these two factors increases the odds of insulin resistance to an even greater degree than would have been expected based on their individual contributions."
In the study, obese individuals who had healthy levels of vitamin D had insulin resistance almost 20 times more often than the overall study population. But in obese individuals whose serum vitamin D was low, insulin resistance was much higher: about 32 times more common than the average.
Senior author Dr. Longjian Liu, an associate professor in the School of Public Health, noted, "It's not clear whether obesity itself causes a low vitamin D level or if it's the other way around."
Vitamin D is stored in adipose fat tissues, making it unavailable for the body to use; as a result, people who are overweight are already more likely to have low levels of serum vitamin D. Vitamin D deficiency is associated with multiple health conditions including diabetes, cardiovascular diseases including stroke, depression, dementia and other conditions.
Kabadi, Liu and co-author Dr. Brian Lee, an assistant professor in the School of Public Health, analyzed data on serum vitamin D levels and indicators of insulin resistance and diabetes from 5,806 respondents to a major national health survey, the National Health and Nutrition Examination Survey (NHANES). This was the first study of the association between vitamin D and diabetes risk for obese patients using a large, nationally representative sample of adults. The survey reported data from individuals at a single point in time and was therefore unable to determine whether there is a cause-and-effect relationship among vitamin D, obesity and insulin resistance.
Further studies could indicate whether vitamin D supplements are effective at reducing the risk of insulin resistance and diabetes in obese individuals. If so, the authors noted that it would be an inexpensive and practical prevention strategy compared to the difficulty involved in healthy weight loss.
Liu said that vitamin D supplements may be useful for people who are overweight or obese to help control diabetes, but he cautioned that too much vitamin D can cause side effects such as weakness and fatigue. In addition, vitamin D deficiency is just one of many known risk factors associated with insulin resistance and diabetes. "Therefore, to control diabetes, we need to have comprehensive prevention strategies. For example, physical activity may be the most cost-effective way to control weight and subsequently to control conditions including diabetes and heart disease," Liu said.
