The human body and all living creatures for that matter have a biological clock entranced and synchronized by day and night (light and dark) cycles, what is called the 24-hour circadian rhythm. As humans age their inability to maintain synchronous sleep/wake cycles shortens lifespan. It is no surprise then to learn that with advancing age those individuals who retain uninterrupted nighttime sleep cycles tend to live longer.
Likewise, exposure of animals to artificially short or long light/dark cycles shortens their lifespan.
Just about everything that is taking place physiologically in the human body is staged and timed by the day/night cycle and if it gets out of sync there is a physiologic penalty to be paid.
Researchers write that "resetting the biological clock" can restore wellbeing and prolong lifespan.
The body's rhythmic activity is controlled in the brain
The loss of ability to maintain so-called circadian (24-hour) rhythms is accompanied by a reduction in the size of the suprachiasmatic nucleus (SCN), a pair of neuron clusters within the hypothalamus of the brain that directly receives light input from the retina of the human eye. Transplantation of young for old SCN in aged animals prolongs the lifespan of laboratory animals.
Changes with advancing age in the SCN are largely controlled by epigenetics, the modifiable dynamic aspect (protein making) of genes rather than the inherited structure of genes (order of nucleotides on the DNA ladder) called mutations. This means aging is modifiable.
Diet and biological rhythm
The health and longevity of modern human populations is complicated by high-fat, high-sugar/carbohydrate diets and light pollution, which throw our biological clock out of whack.
The diet also influences the SCN. For example, infusion of glucose sugar alters the activity of genes in the SCN. Caffeine affects circadian rhythms. The red wine molecule resveratrol also alters clock gene rhythms.
Prolonged periods of non-eating are also beneficial. Intermittent every-other-day fasting extends the life of laboratory animals.
Calorie restriction, circadian (24-hour day-night) rhythms and lifespan are interrelated. Calorie restriction resets the biological day/night (circadian) clock.
Calorie restriction (food deprivation, 30-40% less calories, but not starvation) activates the sirtuin1 survival gene during the day.
Calorie restriction (fasting) increases longevity via regulation of the day/night rhythm. Caloric restriction in aged animals increases longevity, improves memory/thinking, and reduces markers and the onset of brain disease. Relatively brief periods of calorie restriction are sufficient to increase sirtuin1 gene protein levels in the hippocampus. Calorie restriction can entrain (synchronize) the SCN.
There are two central dietary components that block the starvation signal whose removal results in lifespan extension: amino acids and glucose (sugar).