Vitamin D Status in Japanese Young Women in 2016-2017 and 2020: Seasonal Variation and the Effect of Lifestyle Including Changes Caused by the COVID-19 Pandemic.

Avoidance of sunlight and self-restraint due to the COVID-19 pandemic may contribute to reduced vitamin D status. This study provides comparable data on vitamin D status in Japanese young women and assesses the effect of lifestyle, including changes caused by the COVID-19 pandemic, on vitamin D status. In study 1, 39 young healthy Japanese women aged 21-25 y were recruited from May 2016-June 2017. Serum 25-hydroxyvitamin D (25OHD) concentration and diet and lifestyle information were obtained from participants each month (n=124). In study 2, using the same parameters as study 1, young women aged 21-23 y (n=10) were recruited in September 2020. In the results of study 1, we found the frequencies of vitamin D deficiency (25OHD<20 ng/mL) in spring, summer, fall, and winter were 90.5%, 62.5%, 81.5%, and 91.3%, respectively. The substantial difference of serum 25OHD concentration was obtained in spring (Δ3.6 ng/mL) and summer (Δ5.1 ng/mL) depending on the frequency of sunscreen use (0-2 d/wk, 3-7 d/wk). In study 2, serum 25OHD concentration in September 2020 was extremely lower than in September 2016 (13.2 ng/mL vs. 21.7 ng/mL). The number of days spent outside in 2020 decreased drastically compared with 2019. In conclusion, vitamin D deficiency was highly common in Japanese women in their early 20s, and frequent sunscreen use contributed to low vitamin D status. Moreover, because the decrease in days outside due to the COVID-19 pandemic obviously resulted in a decline in vitamin D status, both appropriate sunbathing and increased dietary vitamin D intake are recommended to young women.

Association between 25-hydroxyvitamin D levels and COVID-19 severity.

BACKGROUND AND AIMS: Despite reports on the impact of vitamin D status on coronavirus disease 2019 (COVID-19) severity, the association between low vitamin D status and severe COVID-19 remains unclear. Moreover, researchers have not determined the aforementioned association in Japanese patients. This study aimed to investigate the association between 25-hydroxyvitamin D [25(OH)D] levels and COVID-19 severity in Japanese patients. METHODS: This retrospective observational study included 117 consecutive patients with COVID-19 admitted to the Kobe City Medical Center General Hospital between October 01, 2020, and January 31, 2021. We measured the serum 25(OH)D levels using blood specimens collected within 5 days of hospital admission using liquid chromatography-tandem mass spectrometry. RESULTS: There were 21 (17.9%), 73 (62.4%), 19 (16.2%) and 4 (3.4%) patients with severe deficiency (<10 ng/mL), deficiency (10-<20 ng/mL), insufficiency (20-<30 ng/mL), and sufficiency (≥30 ng/mL) of vitamin D, respectively. In univariate logistic regression analyses, lower serum 25(OH)D levels [odds ratio (OR) 1.18 per 1 ng/mL decrease, 95% confidence interval (CI) 1.04-1.33, p = 0.007] were significantly associated with invasive mechanical ventilation (IMV) or death. In a multivariate logistic regression analysis, low serum 25(OH)D levels [OR 1.22 per 1 ng/mL decrease, 95% CI 1.06-1.40, p = 0.005] were significantly associated with IMV or death. The cut-off value of serum 25(OH)D levels was 10.4 ng/mL, calculated by the receiver operating characteristic curve to detect the requirement for IMV or death. CONCLUSIONS: To the best of our knowledge, this is the first study to assess the association between vitamin D status and COVID-19 severity in Japanese patients. Low serum 25(OH)D level was detected as an independent risk factor for severe COVID-19 among Japanese patients.