The answer is simple: work on positive perceptions!
Positive perceptions of the mind enhance health by engaging immune functions, while inhibition of immune activities by negative perceptions can precipitate dis-ease. Those negative perceptions can also create debilitating, chronic psychological stress that has a profound and negative impact on gene function.
Research on mice has show, for example, that long-term exposure to stress hormones leaves a lasting mark on the genome and modulates the behavior of genes that control mood and behavior.
To see if stress might epigenetically influence genes involved in corticosterone (the rodent version of cortisol), for four weeks control mice drank plain water without this glucocorticoid hormone. Mice who received corticosterone displayed characteristics of anxiety in behavioral tests. Assessment of gene activity showed that these mice had a significant increase in Fkbp5, a protein whose human equivalent has been linked to mood disorders, including depression and bipolar disease. (Lee 2010)
Lee, R. S., K. L. Tamashiro, et al. (2010). “Chronic Corticosterone Exposure Increases Expression and Decreases Deoxyribonucleic Acid Methylation Fkbp5 in Mice.” Endocrinology 151 (9): 4332-4343.