Researchers assed people’s emotional styles for two weeks then exposed them to the common cold virus. Those with a positive emotional style showed more resistance to the virus and fewer symptoms int he weeks following exposure.

Cohen S, Doyle WJ, Turner RB, Alper CM, Skoner DP. Emotional style and susceptibility to the common cold. Psychosom Med. 2003 Jul-Aug;65(4):652-7. doi: 10.1097/01.psy.0000077508.57784.da. PMID: 12883117.