Vitamin D Status Relates to Skin Colors at Sunlight Exposure Areas Stronger Than Non-Sunlight Exposure Areas in Non-Black Population

Presentation Number: SAT 335
Date of Presentation: April 2nd, 2016

Nipith Charoenngam*1, Rachawit Sethpakdee2 and Sutin Sriussadaporn3
1Faculty of Medicine Siriraj Hospital Mahidol University, Bangkok, Thailand, 2Faculty of Medicine Siriraj Hospital Mahidol University, 3Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand

Abstract

Repeated sunlight exposure (SE) results in increased skin vitamin D (D) synthesis and darkening of skin color at SE areas (1, 2). Therefore, skin colors at SE and non-SE areas might differently reflect the amount of SE and D status. This study aimed to examine the relationships among skin colors at SE and non-SE areas, amount of SE, and D status in non-black population such as Thais. Subjects were assessed for serum 25-OHD, daily SE time (DSET), and skin colors at outer (OA) and inner (IA) aspects of arms representing SE and non-SE areas, respectively using von Luschan skin color tiles (VLSC) of which the color score ranging from lightest of 1 to darkest of 36 (3). The VLSC of <21, 21-<25, and >=25 was classified as light (LB), medium (MB), and dark (DB) brown skin colors, respectively.  Subjects who had D supplement or conditions known to affect D metabolism were excluded. Serum 25-OHD levels of <25 ng/dl were defined as D insufficiency (DI).  Data were expressed as mean ± SD (range) or percentage. There were 386 cases (129 men and 257 women) with the age of 63.9 ± 11.1 (26-91) y.  Serum 25-OHD was 25.1 ± 9.9 (3.0-70.0) ng/ml. DSET was 62.8 ± 86.9 (0 – 630) min/d. VLSC of OA was 23.0 ± 1.7 (19-27) with LB in 30 cases (7.8%), MB in 287 (74.4%), and DB in 69 (17.9%). VLSC of IA was 21.6 ± 1.7 (18-27) with LB in 136 cases (35.2%), MB in 241 (62.4%), and DB in 9 (2.3%). There were differences between VLSC of OA and IA (p <0.0001). There were positive correlations between DSET and 25-OHD (R = 0.24, p <0.0001), DSET and VLSC of OA (R = 0.21, p <0.0001), DSET and VLSC of IA (R = 0.19, p <0.005), 25-OHD and VLSC of OA (R = 0.26, p <0.0001), 25-OHD and VLSC of IA (R = 0.17, p <0.001), and VLSC of OA and IA (R = 0.70, p <0.0001).  There were differences in 25-OHD and prevalence of DI among subjects with LB, MB, and DB of OA (18.3 ± 8.4 ng/dl, 80.0% vs. 24.8 ± 9.7 ng/dl, 55.7% vs. 28.9 ± 10.1 ng/dl, 36.2%) (p <0.05). DSET in subjects with LB, MB, and DB of OA were 34.5 ± 28.4, 56.7 ± 76.1, and 103.8 ± 128.8 min/d, respectively, with significant differences between, LB vs. DB (p <0.0005), MB vs. DB (p <0.0001), but not LB vs. MB.  There were significant differences in DSET but not in 25-OHD and prevalence of DI among subjects with LB, MB, and DB of IA (47.8 ± 67.1 vs. 69.4 ± 90.0 vs. 138.3 ± 197.2 min/d) (p <0.05).  Multiple logistic regression showed that the independent factors associated with sufficient D status were male sex (OR = 2.5, 95% CI = 1.58 – 3.94), MB at OA (OR = 2.9, 1.13 – 7.52), DB at OA (OR = 5.6, 1.94 – 16.14), DSET of 10-<30 min/d (OR = 2.4, 1.20 – 4.69), DSET of 30-<120 min/d (OR = 2.6, 1.42 – 4.76), DSET of >120 min/d (OR = 3.3, 1.50 - 7.09). In conclusions, in non-black population, serum 25-OHD, D status and skin colors at SE areas independently relate to amount of SE in dose dependent manners. The relationships are stronger at SE areas than non-SE areas.  D status can be simply predicted by assessment of amount of SE and skin colors at SE areas of upper arm and forearm using von Luschan skin color tiles.

 

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