Lower Vitamin D Levels Linked to Type 1 Diabetes

Nancy A. Melville

August 28, 2012

August 28, 2012 — Children with type 1 diabetes mellitus show lower levels of serum vitamin D than those without the disease, even in a subtropical region of Australia, where sunlight is in abundance, according to a study published online August 23 in Pediatric Diabetes.

Vitamin D, synthesized in the skin through ultraviolet B radiation, is considered to be particularly important in the inflammatory process of type 1 diabetes, helping to modify an immune response that destroys pancreatic islet cells.

Previous studies have shown low levels of 25-hydroxy vitamin D (25OHD), measured in serum as a marker of vitamin D status, among people with type 1 diabetes. However, most of those studies have been conducted at high latitudes in northern Europe, where sunlight exposure can be limited part of the year.

In their study, Ristan M. Greer, PhD, from Queensland Children's Medical Research Institute at the University of Queensland, Australia, sought to determine whether the same effect would be seen in a region where residents typically have much more sunlight exposure.

The researchers evaluated the serum 25OHD levels of 56 children with type 1 diabetes and 46 control participants without the disease, all of whom lived in Brisbane, Australia, located at 27.5°S latitude, where sunlight exposure is abundant.

The authors found serum 25OHD levels to be significantly lower in children with type 1 diabetes compared with children without diabetes (mean, 78.7 [95% confidence interval, 71.8 - 85.6] nmol/L vs 91.4 [95% confidence interval, 83.5 - 98.7] nmol/L, respectively; P = .02). These levels remained lower after adjustment for covariates, including mean ambient ultraviolet radiation index, as the majority of participants with type 1 diabetes had their vitamin D measured in the fall and winter, whereas the control patients were assessed in the spring and summer months.

Children with type 1 diabetes had lower self-reported levels of outdoor exposure and mean ultraviolet exposure; however, there were no significant differences between the 2 groups in terms of vitamin D receptor polymorphisms, which have been linked with autoantibodies and diabetes-related complications, according to the authors.

The children who had newly diagnosed type 1 diabetes (n = 14), defined as a duration of 30 days or less, had the lowest vitamin D levels, showing levels of 1,25-dihydroxy vitamin D (1,25(OH)2D), the active form of 25OHD, that were lower than those seen in the control patients (median, 89 [interquartile range, 68 - 122 pmol/L] vs 121 [interquartile range, 108 - 159] pmol/L, respectively; P = .03) or in children with established diabetes (median, 137 [interquartile range, 113 - 153] pmol/L; difference between those with newly diagnosed type 1 diabetes vs those with established diabetes P = .01).

The study showed no difference between the groups in terms of the proportion of children who were considered 25OHD deficient: 3 of the 46 children vs 5 of the 56 children with type 1 diabetes (P = .73).

"Our study shows that even at relatively low latitude in an environment of abundant [ultraviolet] exposure, paediatric patients with diabetes have low vitamin D compared to their peers, the effect being more marked in those newly diagnosed, but still present in those with established diabetes," the authors note.

Which Comes First: Diabetes or Low Vitamin D Levels?

The findings raise important questions about the precise role of vitamin D in type 1 diabetes, which could be better assessed with serum vitamin D measurements taken at serial intervals before the onset of diabetes, the authors assert.

"Such studies could establish whether low vitamin D is a consequence of diabetes, in which case steps must be taken to avoid consequences such as low bone density and susceptibility to other diseases in later life," they write.

"[A]lternately[, studies could determine] whether low vitamin D is a risk factor for diabetes, in which case preventive action could be taken for those at risk due to environment, family history, or genetic background," they conclude.

The study was funded by a grant from the Royal Children's Hospital Foundation, Queensland.

Pediatr Diabetes. Published online August 23, 2012. Abstract

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