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Sun May Prevent Type 1 Diabetes

Jun 24, 2008
 

Lack of exposure to the sun could play a role in development of type 1 diabetes and that vitamin D supplementation in early childhood may offer protection against the development of type 1 diabetes. The rate of type 1 diabetes was higher in countries at higher latitudes (r2=0.25, P0.001), where solar irradiation per square meter per day is lower, reported Cedric F. Garland, Dr.P.H., of the University of California San Diego, and colleagues online in Diabetologia.

After adjusting for cloud cover and per capita healthcare expenditures, the researchers also found that ultraviolet B irradiance was negatively correlated with rates of type 1 diabetes (r2=-0.42, P0.05). "This natural experiment found that 25% of the variation in incidence rates [for type 1 diabetes] among regions of the world can be accounted for on the basis of latitude, and that 42% can be accounted for on the basis of solar UVB irradiance and percentage cloud cover, the main atmospheric determinants of vitamin D biosynthesis," the researchers wrote.

They recommended a combination of brief daily exposure to sunlight and dietary vitamin D for all young children, particularly those living in northerly climes.

This study is the latest publication by Dr. Garland at the University of California San Diego, to link sun exposure and vitamin D to a major disease.

The new study is their first to connect sun exposure to a non-malignant disease. Dr. Garland and colleagues said it was prompted by a series of national analyses indicating that, for example, rates of type 1 diabetes are 370 times higher in Finland than in China.

"The pattern follows a latitudinal gradient that is the inverse of the global distribution of ultraviolet B irradiance," they explained. Additionally, several earlier studies had found higher incidence of type 1 diabetes in children with low dietary intake of vitamin D.

The Diabetologia report describes a systematic analysis of type 1 diabetes rates from 51 regions of the world from 1990 through 1994, originally collected by the Diabetes Mondial Project Group.

They confirmed that per capita health expenditures were positively correlated with diabetes rates (P=0.004), but that local UVB irradiance remained a significant predictor of diabetes rates in multivariate analysis.

They cited limitations to their analysis including lack of data on dietary vitamin D intake and on typical attire, which may affect actual skin exposure to sunlight.

It’s also possible, they noted, that UVB exposure prevents type 1 diabetes by mechanisms unrelated to vitamin D. Some studies have suggested that the disease is caused by viral pathogens such as Coxsackie virus, which can be killed on surfaces by exposure to sunlight.

Nevertheless, Dr. Garland and colleagues suggested that children older than one year who live in high latitudes should take 25 to 50 mcg of dietary vitamin D3 daily, especially in winter.

The researchers defined high latitudes as beyond the 30th parallels, which covers the entire United States except for Hawaii, south Texas, and the Florida peninsula.

They added that being outdoors in sunlight for a few minutes a day can substitute for some but not all the recommended dietary vitamin D intake.

"Further epidemiological studies would be desirable on the effect of serum 25(OH)D [vitamin D’s active metabolite] levels and oral intake of vitamin D on incidence of type 1 diabetes," the researchers said.

"In the meantime, public health action seems warranted based on evidence gathered to date from many studies."
A meta-analysis of earlier studies of vitamin D and type 1 diabetes, published in the June issue of Archives of Disease in Childhood by researchers in England, led its authors to offer a similar recommendation.

"Vitamin D supplementation in early childhood may offer protection against the development of type 1 diabetes," wrote Christos Zipitis, M.D., of the Stockport NHS Trust, and colleagues after reviewing five observational studies of vitamin D intake and rates of type 1 diabetes.

Practice Pearls:

  • Explain to interested patients that the study found lack of exposure to sunlight may be related to development of type 1 diabetes.
  • Note that the researchers recommended that young children receive brief daily exposure to sunlight, as well as dietary vitamin D for those living in high latitudes, including most of the U.S.
  • Point out that the proposed preventive effect on type 1 diabetes has not been confirmed in a prospective trial and these studies cannot prove causality of the association.

Diabetologia:Mohr S, et al "The association between ultraviolet B irradiance, vitamin D status and incidence rates of type 1 diabetes in 51 regions worldwide" Diabetologia 2008; DOI: 10.1007/s00125-008-1061-5

Archives of Disease in Childhood: Zipitis C, et al "Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and meta-analysis" Archives of Disease in Childhood 2008; 93: 512-17.

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DID YOU KNOW:
High Postprandial Levels Independently Associated With Mortality:Results of a new study show which information from oral glucose tolerance tests can be used independently predict mortality.The most significant independent risk factor for mortality was the higher 120-minute glucose.  When examined separately, the 100-minute and 120-minute glucose measures were also independent predictors of mortality, as were the fasting and 100-minute insulin levels. However, when examined together, the higher 120-minute glucose level was the only significant independent risk factor for mortality. These findings suggest the value of using the OGTT in clinical practice, according to the researchers. See this weeks’ Item # 7
Diabetes Care. 2008;31:1026-1030.

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