There are just numerous examples for this. I am in the field

of dermatopathology (skin pathology), and also had some limited experience in clinical dermatology.

Skin cancers like melanoma, and non-melanoma skin cancers, such as squamous cell carcinoma are directly related to sun exposure, particularly UVB. If you claim that if one's mind is healthy, and one does't need to worry about skin cancer as long as his/her mind is healthy, then you are doing a great harm to the people because the key issue here is to avoid too much sun exposure, nothing to do with if you are happy or sad.