Relationship between skin color, sun exposure, UV protection, fish intake and serum levels of vitamin D in Japanese older adults

Abstract

Purpose This paper aims to observe the possible relationship between skin color, sun exposure level, UV protection and food intake and serum levels of 25(OH) D in Japanese older adults. Design/methodology/approach Elderly (n = 131; 65-93 years old), followed by the Tokyo Metropolitan Institute of Gerontology in the Kusatsu (36°N) received a self-applicable questionnaire about the quantity and quality of the daily sun exposure and behavior to avoid the sun. A color analyzer measured each red (R), green (G) and blue (B) component of skin color, and dietary vitamin D was estimated by food frequency questionnaire. Serum 25(OH) D levels were collected and categorized as sufficiency (>30 ng/mL), insufficiency (between 20 and 30 ng/mL) and deficiency (<20 ng/mL). Findings High proportion of participants had insufficiency (53 per cent) and deficiency (25 per cent) levels of 25(OH) D. Insufficiency levels were more prevalent in women (57 per cent, p = 0.048) and in participants that use gloves (49 per cent, p = 0.054) and sunscreen on face (76 per cent, p = 0.003) as a sun protection way. Participants with sufficiency levels of 25(OH) D presented lower values of R (p = 0.067), G (p = 0. 007) and B (p = 0.001) of skin color (what is meaning darker skin) and a higher fish intake (12 times per week). Research limitations/implications The study is a cross-sectional design and brings a potential for measurement error in the recorded subjective variables. There is a memory bias in self-reported sun exposure and food consumption; however, in the multivariate analysis, it was demonstrated a significant association. Second, although the authors have sought to evaluate a number of variables that could affect the skin’s ability to synthesize vitamin D, there are many other factors that may affect this ability that could not be accounted for. Another limitation was the assessment of self-reported ultraviolet exposure data rather than direct measurement of exposure. Practical implications It was also concluded that darker skin color (a surrogate of longer-term sun exposure) participants had a lower prevalence of vitamin D insufficiency in this ethnic homogeneous population. When accessing patients’ skin color, the clinician must account for his or her ethnicity. Social implications Governments should regulate supplementation or food fortification with vitamin D, with special focus in countries with geographical location of insufficient solar radiation for skin synthesis of this vitamin. With this, it becomes a priority that a safe sun exposure ensures the sufficient serum levels of 25 (OH) D without the use of supplements. Originality/value This report was the first to analyze skin color components associated to vitamin D levels, finding that blue and green colors were significant. The clinical implication of this find is yet to understand. It was also concluded that darker skin color (a surrogate of longer-term sun exposure) participants had a lower prevalence of vitamin D insufficiency in this ethnic homogeneous population. When accessing patients’ skin color, the clinician must account for his or her ethnicity.