Life extension refers to an increase in maximum or average lifespan, especially in humans, by slowing own or reversing the processes of aging. Average lifespan is determined by vulnerability to accidents and age-related afflictions such as cancer or cardiovascular disease. Extension of average lifespan can be achieved by good diet, exercise and avoidance of hazards such as smoking and excessive eating of sugar-containing foods. Maximum lifespan is determined by the rate of aging for a species inherent in its genes and probably by certain environmental factors. Currently, the only widely recognized method of extending maximum lifespan is calorie restriction. Theoretically, extension of maximum lifespan could be achieved by reducing the rate of aging damage, by periodic replacement of damaged tissues, or by molecular repair or rejuvenation of deteriorated cells and tissues.