What Is Mitochondrial Health — And Why It Matters After 40

Mitochondria are often described as the powerhouses of the cell — a phrase so common it has become almost meaningless. But the science behind mitochondrial function is genuinely remarkable, and the consequences of mitochondrial decline are increasingly recognised as central to how we age. Understanding what mitochondria do, why they deteriorate, and what can be done to support them is one of the most important questions in modern metabolic medicine.

What Mitochondria Actually Do

Every cell in the human body — with the exception of red blood cells — contains mitochondria. A typical liver cell contains between 1,000 and 2,000 of them; a heart muscle cell may contain up to 5,000. Their primary function is to convert nutrients into adenosine triphosphate (ATP), the molecule that powers virtually every biological process: muscle contraction, protein synthesis, nerve signalling, and immune response.

Beyond energy production, mitochondria regulate calcium signalling, control the intrinsic pathway of programmed cell death (apoptosis), produce heat, and play a central role in the cellular stress response. They are, in effect, the metabolic control centres of the cell.

Why Mitochondrial Function Declines With Age

Mitochondrial decline is one of the most well-documented features of biological aging. Several mechanisms drive this deterioration. First, mitochondrial DNA (mtDNA) accumulates mutations over time because, unlike nuclear DNA, it has limited repair capacity and sits in close proximity to the reactive oxygen species (ROS) generated during energy production. Second, the process of mitophagy — the cellular quality control mechanism that identifies and removes damaged mitochondria — becomes less efficient with age. Damaged mitochondria that would normally be cleared begin to accumulate, impairing the overall function of the mitochondrial network.

"Mitochondrial dysfunction is a hallmark of aging and is associated with a wide range of age-related conditions including reduced muscle strength, metabolic dysregulation, and impaired cognitive function." — López-Otín et al., Cell, 2023

A third factor is the decline in NAD+ levels that accompanies aging. NAD+ is an essential cofactor for mitochondrial energy metabolism, and its depletion impairs the efficiency of the electron transport chain — the core machinery of ATP production.

The Measurable Consequences

The practical consequences of mitochondrial decline are not abstract. Research consistently links reduced mitochondrial function to lower muscle strength and endurance, impaired glucose metabolism, increased fatigue, and slower recovery from physical exertion. A landmark study published in Nature Metabolism in 2022 demonstrated that supplementation with Urolithin A — a compound that activates mitophagy — improved muscle strength by 12% and endurance capacity in adults aged 40–64 compared to placebo over a four-month period.

What Can Be Done

The good news is that mitochondrial function is not fixed. Several lifestyle interventions have strong evidence for supporting mitochondrial health: aerobic exercise (particularly zone 2 training), resistance training, caloric restriction, and adequate sleep all stimulate mitochondrial biogenesis — the creation of new mitochondria. Nutritional strategies including adequate protein intake, omega-3 fatty acids, and specific micronutrients such as magnesium also play a supporting role.

At the supplementation level, compounds that activate mitophagy — particularly Urolithin A — have attracted significant clinical interest. Unlike many supplements, Urolithin A has been studied in randomised controlled trials with measurable endpoints, making it one of the more evidence-grounded options in this space.

A Note on Supplement Use

Supplements designed to support mitochondrial function should be understood as one component of a broader metabolic strategy — not a substitute for the lifestyle foundations. They are most relevant for adults who are already engaging in structured exercise and nutrition, and who want to add a targeted, evidence-informed layer of support. As with any supplement, individuals with existing health conditions or on prescription medication should consult their doctor before starting.