What is the relationship between genetic variation and human health?

Genetic variation is highly related to human health. For example, some tumors have a family history, as well as diabetes, hypertension and mental illness, all of which have great genetic factors. However, if we pay attention to avoid them the day after tomorrow, one generation will not get sick again, and the next generation will become less likely to get sick. This is genetic variation, which is good or bad for people's health.