Association of 25-Hydroxyvitamin D3 Levels in Adult New Zealanders with Ethnicity, Skin Color and Self-Reported Skin Sensitivity to Sun Exposure

The study aim was to determine the contribution of ethnicity, objectively measured skin color and skin reaction-to-sun exposure to variations in 25-hydroxyvitamin D-3 [25(OH)D-3]. A multiethnic sample (European, Maori, Pacific and Asian) of 503 adult volunteers aged 18-85 years, recruited from Auckland and Dunedin in New Zealand, answered a questionnaire on sun exposure and self-defined ethnicity. Skin color was measured using a spectrophotometer and the Individual Typology Angle (ITA) calculated. A blood sample was collected 4 weeks later to measure 25(OH)D-3. 25(OH)D-3 was associated with ethnicity, but not self-reported skin reaction-to-sun exposure. Amongst the ethnic groups, Asians had the lowest mean 25(OH)D level (37.0 nmol L-1) and Europeans with lighter colored skin had the highest (57.9 nmol L-1). An association also was seen between 25(OH)D-3 and skin color, with an increase of 2-3 nmol L-1 per 10 degrees increase in ITA value, indicating higher 25(OH)D-3 with lighter skin color; but much of this association disappeared after adjusting for ethnicity. In contrast, ethnicity remained associated with 25(OH)D-3 after adjusting for ITA skin color and skin reaction-to-sun exposure. These results indicate that self-defined ethnicity was a major determinant of variations in serum 25(OH)D-3, while objective measures of skin color explained relatively little additional variation.