Vitamin D supplementation of initially vitamin D‐deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB/c dams were fed a vitamin D(3)‐supplemented (2280 IU/kg, VitD(+)) or nonsupplemented (0 IU/kg, VitD(−)) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD(−) diet were switched to a VitD(+) diet from 8 weeks of age (VitD(−/+)). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid (BALF) of VitD(−) mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D(3). There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD(+) mice compared to VitD(−) mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D(3)‐containing diet (VitD(−/+)). Reduced total IgM levels were detected in BALF and serum of VitD(−/+) mice compared to VitD(+) mice. Lung mRNA levels of the vitamin D receptor (VDR) were greatest in VitD(−/+) mice. Total IgG levels in BALF were greater in mice fed the vitamin D(3)‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D(3) suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.