Serum 25OHD, Skin Phototype and Sun Index from Adolescence to Old Age: Data from a Large Sample of Individuals with High Rates of Sun Exposure Living in the Tropics

Presentation Number: SAT 332
Date of Presentation: April 2nd, 2016

Francisco Farias Bandeira*1, Leonardo Bandeira2, Aline Correia1, Cyntia Lucena1 and Maria Paula Bandeira3
1Division of Endocrinology, Diabetes and Bone Diseases, Agamenon Magalhaes Hospital, Univertsity of Pernambuco Medical School, Recife PE, Brazil, 2Columbia University, College of Physicians and Surgeons, New York, NY, 3Instituto de Medicina Integral de Pernambuco, Recife PE, Brazil

Abstract

Introduction: The main source of vitamin D in humans is the cutaneous synthesis induced by ultraviolet (UV) irradiation but two factors limit the regular or repeated exposure to sun light, especially in areas with its abundance such as the tropics: the increased risk of skin cancer and the progressive pigmentation of the skin which creates a natural barrier to the UV action.  

Objective:To evaluate the relationship of serum 25OHD levels with sun exposure and skin phototype in 986 individuals living in the city of Recife, Brazil (8° S).

Methods:Sun index (hours of sun exposure per week multiplied by the fraction of body surface area exposed) and skin phototype (Fitzpatrick’s classification) were evaluated and serum 25OHD and PTH were measured. Subjects with regular sunscreen use and vitamin D supplementation were excluded.

Results:Mean age was 53.15±18.08 (range from 13 to 82) years; 55.4% male; 60.6% had a skin phototype between III-IV; Mean serum PTH was 40.70±29.99 pg/ml and 25OHD 26.06 ±10.37 ng/ml. Prevalence of vitamin D deficiency was 72% (25OHD < 30 ng/ml) and 28.5% had serum 25OHD < 20 ng/ml.  These subjects were older than those with 25OHD above 30 ng/ml (60.47±15.42 vs 57.40±17.91 years old, p = 0.036), had lower sun index (4.39±4.11 vs 5.80±5.58, p = 0.006) and had lower serum PTH (50.95±33.29 vs 36.45±26.31 pg/ml, p<0.001). Mean 25OHD levels among those with sun index of 0 - > 7 ranged from 25.30±8.45 to 27.85±10.86 ng/ml (p = 0.012) and between those of skin types I-VI ranged from 20.11±8.36 to 26.57±11.05 ng/ml (p = 0.158). Prevalence of vitamin D deficiency among individuals with sun index between 0 - > 7 ranged from 29.5% to 21.3% (25OHD <20 ng/ml) and from 71.2 to 67.9% (25OHD < 30 ng/ml); and among those with skin phototype between I-VI ranged from 55.6% to 23.9% (25OHD <20 ng/ml) and from 88.9 to 65.7% (25OHD < 30 ng/ml). From 92 subjects between 13 and 16 years of age, 53.2% had serum 25OHD < 30 ng/ml and 18% < 20 ng/ml. In these early-adolescents, there were significant differences between subjects with 25OHD < 20 ng/ml compared to those with 25OHD > 30 ng/ml in sun index (3.5 vs 9.0; p= 0.005), highly pigmented skins (24.5 vs 43.4%, p=0.01) and the frequency of regular outside recreation activities (22.5 vs 46.5%, p=0.015).

Conclusion: Higher sun exposure rates led to more tanned skins but also, less vitamin D deficiency. However, most individuals with very high rates of sun exposure in daily life had serum 25OHD below 30 ng/ml, suggesting that skin tanning limits the progressive rise in serum 25OHD towards optimal concentrations.

 

Nothing to Disclose: FFB, LB, AC, CL, MPB