What are mitochondria, and can you make them younger or more energetic?
Regular exercise is by far the best-supported means of keeping mitochondria healthy; NAD+ supplements sound appealing but have not yet been sufficiently proven in humans.
Mitochondria are small structures found in almost every cell of your body. They convert nutrients into ATP, the fuel that powers virtually everything inside the cell: muscle contraction, cell division, brain function. But they do more than supply energy. They respond to stress, send signals to other tissues, and play a role in ageing and disease. When they function poorly, the consequences are felt throughout the entire body.
Exercise is the most powerful tool we know of for improving mitochondria. Physical exertion activates a switch inside the cell that drives the production of new mitochondria in muscles. That same switch also helps clear away damaged mitochondria. This effect has been demonstrated in humans, although the precise mechanism has not yet been fully mapped. Fasting and short-term energy deficit work via a similar pathway: they activate a protein that prompts the cell to carry out quality control on its mitochondria.
NAD+ is a molecule that mitochondria need in order to function properly. As you age, the amount of NAD+ in your cells declines, and this is associated with reduced mitochondrial activity. Supplements that are supposed to raise NAD+ are being studied extensively, but whether they actually achieve that effect in humans and translate into more energy or slower ageing has not yet been adequately demonstrated by the current body of research.
Hereditary conditions in which the DNA of the mitochondria themselves is damaged can lead to serious disease. These conditions are clinically very diverse and difficult to treat, although promising therapeutic developments are under way. This is distinct from the gradual mitochondrial decline that comes with normal ageing, which is something that lifestyle choices can meaningfully influence.
Cells can also exchange mitochondria through small connecting tubes. This phenomenon was only recently discovered and is studied mainly in cancer research. Whether it tells us anything about healthy ageing remains unknown for now.
Claims about basic function and hereditary diseases are well supported. The effects of exercise on mitochondrial quality have been demonstrated in humans, but the precise mechanisms come largely from animal and cell studies. The role of NAD+ supplements in humans has not yet been convincingly demonstrated in the available abstracts. Mitochondrial transfer between cells is an early-stage area of research.