Figure 1 (A) Mean serum 25-hydroxyvitamin and (B) OICR-9429 concentration parathyroid hormone levels in female Soldiers pre- and post-basic combat training. Serum 25-hydroxyvitamin D, 25(OH)D; parathyroid hormone, PTH. n = 74; values are means ± SD. Asterisks (*) indicate significant differences (P < 0.05) from pre-values. Figure 2 (A) Boxplots of serum 25-hydroxyvitamin D and (B) parathyroid hormone levels in female Soldiers pre- and post-basic combat training by ethnicity. Serum

25-hydroxyvitamin D, 25(OH)D; parathyroid hormone, PTH; basic combat training, BCT. n = 74; non-Hispanic white, n = 39; non-Hispanic black, n = 24; Hispanic white, n = 11. Boxes represent the middle 50th percentile, and vertical lines extend to the 10th and 90th percentiles. Median values are marked by a line within each box. Values below the 10th percentile or above the 90th percentile are identified by solid circles (•). A two-factor repeated measures ANOVA with Bonferroni adjustments was utilized to determine the effects of time and ethnicity on 25(OH)D and PTH levels. Asterisks (*) indicate significant differences between mean values pre- and post-BCT within ethnicities (P < 0.05). adifferences between mean values of non-Hispanic SIS3 mouse whites and non-Hispanic blacks pre-BCT (P < 0.01); bdifferences

between mean values of non-Hispanic blacks and Hispanic whites pre-BCT (P < 0.05); cdifferences between mean values of all ethnic groups post-BCT (P < 0.05). Discussion Vitamin D is a critical nutrient for

active populations, as it contributes to effective bone remodeling and calcium homeostasis. The major finding of this pilot study is that vitamin D status in female Soldiers declines during military training in the summer and early autumn months in the Southeastern US. This finding was unanticipated, as we expected the vitamin D status of female Soldiers to remain static or increase due to sunlight exposure during BCT, as much of the training occurs outdoors during daylight hours. Although further research is required to elucidate the mechanism, we hypothesize that the type of clothing worn during BCT, coupled with potentially inadequate dietary vitamin D intake may contribute to the observed decline in vitamin D status. Recent studies have utilized 25(OH)D values of ≤75 nmol/L as an indicator of DZNeP mw suboptimal vitamin D status [8, 13, 14]. If this cutoff is applied to Glutamate dehydrogenase the data gleaned from the present study, 57% of subjects entered BCT with 25(OH)D levels <75 nmol/L, and 75% completed BCT below the cutoff value, indicating that the majority of Soldiers demonstrated suboptimal vitamin D status during BCT. Our findings demonstrate ethnic differences in vitamin D status. Similar to previous reports, 25(OH)D levels were lowest in non-Hispanic blacks and tended to be highest in non-Hispanic whites [15–17]. Furthermore, vitamin D status declined significantly in non-Hispanic and Hispanic whites, but not in non-Hispanic blacks.