That is called epigenetics and is controlled by environmental factors such a temperature, solar radiation exposure or food or lack of food.

FORBES: Is Ethical Human Genetic Enhancement Possible?

The genetic answer to chronic age-related disease, which predominates in long-living populations, is encoded in the epigenome involved in receiving signals from environmental factors such as food, food deprivation, solar radiation and temperature.

FORBES: Why You Should Fear Giant Databases With Your DNA