OBJECTIVES This study was intended to examine the seasonal differences in outdoor activity times and dietary vitamin D intakes, and explicates their relative impact on improving serum 25-(OH) vitamin D status among Korean young women. METHODS A cross-sectional study was conducted with 135 free-living women aged 19-39 years in Daegu-Kyungbook, Korea. We compared the results from 52 women for the summer and 83 women for the winter. Dietary intake of vitamin D was assessed by 24 hour recall method for non-consecutive three days as well as by food frequency method. Daily outdoor activity times were derived from 24 hour physical activity diary. RESULTS The average dietary intake of vitamin D of the participants by 24 hour recall method was 3.1 microg during the summer, 3.3 microg during the winter, showing no significant difference between the two seasons. Times spent on outdoor activities (p < 0.01) in the summer (= 23.8 +/- 23.6 min) were much longer than that in the winter (= 10.8 +/- 13.4 min). The serum 25-(OH) vitamin D levels of participants were 17.5 +/- 7.5 ng/mL in the summer and 13.4 +/- 4.3 ng/mL in the winter, showing that the latter was significantly lower than that of the former (p < 0.001). The serum 25-(OH) vitamin D levels of subjects were positively related to outdoor activities (r = 0.315, p < 0.05) during the summer, while related to dietary intake (r = 0.252, p < 0.05) during the winter. CONCLUSIONS In order to improve the current vitamin D status of Korean young women, nutrition education programs should focus on increasing more dietary intake especially during the winter, and performing more outdoor activities in other seasons.
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