Impact of Chronic Cold Water Immersion and Vitamin D3 Supplementation on the Hippocampal Metabolism and Oxidative Stress in Rats

Chronic cold exposure is a stressor that may adversely affect the hippocampal structure and cognitive function. Critical for memory formation and learning processes, the hippocampus is particularly susceptible to hypothalamic–pituitary–adrenal (HPA) axis activity and elevated glucocorticoid levels. Vitamin D plays a complex role in regulating mitochondrial function and may provide neuroprotection. This study aimed to investigate the effects of chronic cold exposure on proteins associated with signaling pathways, mitochondrial function, and oxidative stress in the hippocampus of rats and to evaluate the neuroprotective potential of vitamin D3 supplementation. Male Wistar rats (n = 26) were assigned to four groups: control (CON; n = 4), sham stress (WW; n = 6), chronic cold water immersion (CCWI) (CW group; n = 8), and CCWI with 600 IU/kg/day vitamin D3 (VD3) supplementation (CW + D group; n = 8). Exposure to CCWI significantly reduced the hippocampal mass of rats, an effect not reversed by vitamin D3 supplementation. However, vitamin D3 improved mitochondrial function and exhibited antioxidant effects, partially reducing markers of protein and lipid free radicals damage in neural tissue. Our findings demonstrate the antioxidant properties of VD3 and its potential role in mitigating hippocampal damage during prolonged cold exposure, although its neuroprotective effects remain limited.