Vitamin D levels in subjects with and without type 1 diabetes residing in a solar rich environment

Abstract

Objective: Previous studies, largely in northern Europe, have suggested an association between type 1 diabetes and reduced serum 25-hydroxy(OH) vitamin D levels, a concept we tested in individuals residing in a solar-rich region (Florida).

Research design and methods: Serum samples from 415 individuals residing in Florida were cross-sectionally analyzed: 153 control subjects, 46 new-onset type 1 diabetic patients, 110 established type 1 diabetic patients (samples >or=5 months from diagnosis), and 106 first-degree relatives of the diabetic patients.

Results: In this study, 25-OH vitamin D levels (median, range, interquartile range [IQR]) were similar among control subjects (20.1, below detection [bd]-163.5, 13.0-37.4 ng/ml), new-onset type 1 diabetic patients (21.2, bd-48.6, 12.2-30.2 ng/ml), established type 1 diabetic patients (23.2, bd-263.8, 13.8-33.9 ng/ml), and first-degree relatives (22.2, bd-59.9, 12.7-33.1 ng/ml) (P = 0.87). Mean 25-OH vitamin D levels were less than the optimal World Health Organization level of 30 ng/ml in all study groups.

Conclusions: Reduced serum 25-OH vitamin D levels were not specifically associated with type 1 diabetes. The uniform suboptimal 225-OH vitamin D levels, despite residence in a zone with abundant sunshine, support additional dietary vitamin D fortification practices.

Figure 1

25-OH vitamin D levels in cohorts based on parameters of disease, age, or estimated solar exposure. For disease status (A), values are presented as a function of study group with definitions of insufficiency (orange line) and deficiency (red line) provided. With respect to age (B), values for all study participants independent of cohort are shown with the definitions of insufficiency and deficiency as defined in A along with age correlation (blue line). C: Estimated average UVB exposure for the entire study population is presented. UVI climatological data were obtained from the National Weather Service (NWS) and U.S. Environmental Protection Agency (EPA) Web sites (http://www.cpc.ncep.noaa.gov and http://www.epa.gov) to determine relative UV exposure. Based on data for the previous 5 years, for the proximate city of Jacksonville, Florida, we established the mean UV exposure for each month: January, 3.215; February, 4.08; March, 5.96; April, 7.68; May, 8.238; June, 8.578; July, 8.976; August, 8.254; September, 6.902; October, 5.11; November, 3.694; and December, 2.79. The numbers correspond to the UVI scale (1–11+) developed by the NWS and EPA and implemented by the World Health Organization. The samples were grouped according to month drawn and placed into one of four possible 3-month blocks, each block formed on the basis of similar UVB indexes. The 25-OH vitamin D levels (reported as median, range, IQR) for the November/December/January group of 112 samples (20.7, bd–263.8, 12.7–33.6 ng/ml) with an average estimated UV exposure of 3.23. The October/February/March group of 113 samples (20.8, bd–146.8, 12.7–31.5 ng/ml) with an average estimated UV exposure of 5.05. The September/April/May group of 84 samples (19.3, bd–163.5, 14.0–36.9 ng/ml) with an average estimated UV exposure of 7.61. The June/July/August group of 106 samples (23.9, bd–82.9, 13.4–35.6 ng/ml) with an average estimated UV exposure of 8.60.