Can cold exposure improve immune function?

Cold exposure can indeed affect immune function. According to Andrew Huberman, repeated cold exposure over a period of six weeks, approximately three times a week, can lead to trends toward increases in immune system markers, including plasma concentrations of interleukin 6 and total numbers of various T lymphocytes and B lymphocytes. However, he notes that these effects are trends rather than statistically significant changes, and there is no direct evidence of how these trends may translate to actual resistance against specific viruses or bacteria 1.

Moreover, cold exposure can increase the levels of epinephrine and norepinephrine, which can have pro-immune effects in promoting the activation of immune cells and molecules. However, if these two molecules are elevated chronically, and especially if they are elevated late in the day over many days, they can lead to reductions in the number and efficiency of immune cells 2.

In another instance, deliberate cold exposure has been linked to lower inflammation in the body, which could have potential implications for preventing lifestyle diseases including certain mental illnesses like depression and anxiety 3.

It's also important to note Dr. Huberman's caution against using deliberate cold exposure if feeling ill, as there's no clear evidence to suggest that it would be beneficial and it may even be contraindicated when sick 4.

Always consider the context and potential risks, and consult a healthcare professional for personal medical advice.