Are low sun exposure and/or vitamin D risk factors for type 1 diabetes?

Abstract

The global variation in type 1 diabetes (T1D) incidence rates is one of the most significant observed for any non-communicable disease. Geographical patterns in incidence suggest that low sun exposure may contribute to the wide disparity, with incidence rates generally increasing with distance from the Equator. T1D development is associated with hyperactivity of the adaptive immune system leading to autoimmune destruction of insulin-secreting pancreatic β cells. Both exposure to ultraviolet radiation (UVR) and vitamin D, with their known immunosuppressive effects, have the potential to delay or inhibit the disease. Efforts to confirm the role of UVR by vitamin D dependent and independent pathways in the pathogenesis of T1D have been challenged by inconsistent results among studies. Human observational studies and animal and in vitro experiments indicate that at least some of the benefits of sun exposure come from improved vitamin D status. There is no evidence of benefit for T1D risk of vitamin D supplementation during pregnancy at current recommended levels (400 IU per day); but some evidence supports that higher sun exposure and/or vitamin D sufficiency in pregnancy, or supplementation in early life, decreases T1D risk. Further research is required to confirm an association between UVR exposure and T1D and clarify the mechanisms involved.

Low Sun Exposure and Vitamin D Deficiency as Risk Factors for Inflammatory Bowel Disease, With a Focus on Childhood Onset

“…The variability in results is similar for ulcerative colitis: Most studies show no evidence of a season‐of‐birth effect (Table ), but others show an excess of ulcerative colitis births in spring , summer or winter . The data are much less consistent than for another autoimmune disease, multiple sclerosis , but similar to that for type 1 diabetes . On the basis of the reviewed studies, there is little evidence to support any season (or month)‐of‐birth effect on the risk of Crohn's disease or ulcerative colitis.…”

Higher ultraviolet radiation during early life is associated with lower risk of childhood type 1 diabetes among boys

“…Prior studies have shown that higher 25(OH)D levels in the third trimester, but not in the first or second trimesters, were associated with reduced risk of type 1 diabetes in offspring 15 , 30 – 32 . Of note, however, is current evidence that suggests maternal intake of vitamin D-only supplements during pregnancy at current recommended levels (400 IU) does not reduce risk of islet autoimmunity (IA) or type 1 diabetes among offspring (see 3 for review). It is possible that the current recommended dose is not high enough to provide protection or that the benefits of vitamin D supplementation are limited to those for whom insufficiency is corrected or nuanced to particular VDR polymorphisms 33 .…”

“…This is further supported by worldwide reports of a reduced proportion of children with high-risk HLA genotypes presenting with type 1 diabetes 2 . Seasonal variation in type 1 diabetes incidence (see 3 for review) and higher incidence 4 , 5 and prevalence 6 of type 1 diabetes with higher latitude support an environmental trigger 7 . One candidate environmental factor that varies by both season and latitude is ultraviolet radiation (UVR).…”

“…For example, low sun exposure is now widely accepted as a risk factor for multiple sclerosis 11 , and recent studies have shown inverse associations between UVR exposure and risk of eczema 12 and paediatric inflammatory bowel disease 13 . Previous studies suggest that there may be an optimal exposure window to reduce type 1 diabetes risk, prior to the development of diabetes-related autoantibodies, such as the last few months of gestation 14 , 15 or in the first year of life 3 , 16 – 18 at the time of both beta cell proliferation and maturation of the immune system, allowing for persistent protection. No studies have examined long-term individual-level data on UVR and development of type 1 diabetes.…”

<p>Comorbidities in multiple sclerosis—a plea for interdisciplinary collaboration to improve the quality of life of MS patients</p>

“…A greater distance from the equator (higher latitudes) and the number of months with little sunshine increases the vitamin D deficiency. Other factors such as race, ethnicity (Blacks, Hispanics, Whites), genetic susceptibility, climatic variation, sun-seeking behaviors and clothing habits play a role 108. There are differences between White patients, Blacks or Hispanics of a Mexican background.…”