3 / How to Rebuild Your Energy After 45

By now, we have done two important things. We have stopped treating fatigue as simply “a menopause symptom,” and we have looked for the more obvious drains on energy, including poor sleep, iron loss, inadequate nutrition, metabolic problems, excessive stress, alcohol, medication and too much or too little activity.

The next question is different: how do we actually build a body that produces and uses energy well?

This is where mitochondria, muscle, glucose, oxygen, thyroid hormones, nutrition and recovery come together. It may sound complicated, but the practical strategy is surprisingly clear.

First, understand where your energy actually comes from

Every cell needs energy to function. Much of that usable energy is stored in a molecule called ATP, or adenosine triphosphate. Your mitochondria produce most ATP through a process called oxidative phosphorylation, using energy derived from carbohydrates and fats. Oxygen plays a crucial role in this process, acting as the final electron acceptor in the mitochondrial electron transport chain.

Cellular energy therefore depends on several systems working together: adequate fuel, oxygen delivery, functioning mitochondria, appropriate thyroid signalling and the vitamins and minerals required by metabolic enzymes. This is one reason fatigue rarely has one universal solution.

The goal is not simply to “boost your mitochondria.” It is to make sure the entire energy-producing system has what it needs to function properly.

Build mitochondrial capacity through movement

Mitochondria are remarkably adaptable. Regular exercise stimulates mitochondrial biogenesis, the process through which cells increase their mitochondrial machinery. Aerobic training also improves the ability of skeletal muscle to use oxygen and produce ATP efficiently. This is one reason regular movement can eventually give you greater energy capacity rather than simply using up the energy you already have.

If you are currently exhausted and unfit, however, an extreme exercise programme is not the place to begin. Start with walking and gradually increase duration and intensity. As your capacity improves, include cardiovascular exercise that genuinely challenges your heart and lungs. You do not need to destroy yourself in a workout. You need to give your body a repeated, manageable signal to adapt.

Build muscle because muscle changes how you use fuel

Muscle is not simply something that makes us stronger. It is one of our most important metabolic tissues and a major site of glucose disposal. During muscle contraction, glucose uptake can increase through mechanisms that do not depend entirely on insulin, while regular resistance training can improve insulin sensitivity over time.

This becomes increasingly important after 45 because muscle mass and strength tend to decline with ageing unless we actively protect them. Once fatigue is reasonably controlled, aim for two to three resistance-training sessions each week, progressively challenging the major muscle groups.

This is not primarily about burning calories. More capable muscle means better glucose handling, greater physical capacity and everyday tasks requiring a smaller proportion of your available strength. That is an important part of what rebuilding energy capacity actually means.

Improve metabolic flexibility

A metabolically healthy body can use both carbohydrate and fat as fuel and shift between them according to demand. You do not need to eliminate carbohydrates or remain in ketosis to achieve this. Insulin sensitivity, physical activity, muscle mass, overall energy balance and diet quality all influence how effectively your body handles fuel.

Build meals around adequate protein, fibre-rich plants, appropriate whole-food carbohydrates and healthy fats, while reducing the constant exposure to refined carbohydrates and ultra-processed foods that provide plenty of energy but relatively little nutritional value. Movement matters too. A short walk after meals can help skeletal muscle dispose of glucose, resistance training improves glucose handling over time, and aerobic exercise increases the muscle's oxidative capacity.

Metabolic flexibility is built through physiology, not through a single food rule.

Stop under-fuelling your body

You cannot manufacture ATP from good intentions. If you chronically consume less energy than your body requires while simultaneously expecting it to work, exercise and recover, something eventually gives. This is particularly relevant when women respond to midlife weight gain with increasingly aggressive calorie restriction.

Protein helps preserve muscle and provides amino acids needed throughout the body. Carbohydrate supplies readily available glucose and replenishes glycogen, particularly around more demanding exercise. Dietary fat provides essential fatty acids, supports cell membranes and supplies another major energy source. Micronutrients matter too because energy metabolism depends on numerous vitamin and mineral cofactors.

The solution is not overeating. It is adequate nourishment rather than chronic depletion.

Make sure oxygen can reach your cells

Even perfectly functioning mitochondria cannot produce energy efficiently if oxygen delivery is compromised. Haemoglobin inside red blood cells carries oxygen from the lungs to tissues, and iron is an essential component of haemoglobin. This is one reason iron deficiency and anaemia can cause profound fatigue and reduced exercise capacity.

Iron also participates directly in mitochondrial enzymes and the electron transport chain, so its role extends beyond haemoglobin. If heavy perimenopausal bleeding has depleted iron stores, no amount of “mitochondrial support” compensates for failing to identify and correct the underlying problem.

Iron should not be taken blindly. Test first, treat documented deficiency appropriately and investigate why it developed.

Thyroid hormones help set the metabolic pace

Thyroid hormones influence energy expenditure and mitochondrial function throughout the body. In hypothyroidism, insufficient thyroid hormone action slows numerous metabolic processes and can contribute to fatigue, cold intolerance, constipation, cognitive slowing, changes in weight and reduced physical capacity.

Persistent fatigue accompanied by compatible symptoms therefore deserves proper thyroid assessment rather than automatically being labelled menopause. But the opposite mistake is also common. Feeling tired does not automatically mean your thyroid needs “support,” and taking thyroid hormones when thyroid function is normal is not an energy strategy.

Again, identify the bottleneck before trying to treat it.

Correct nutrient deficiencies, not theoretical ones

Several micronutrients participate directly in cellular energy production. Iron is involved in oxygen transport and mitochondrial electron transfer. Vitamin B12 and folate are required for normal red blood cell formation and other cellular processes. Magnesium participates in hundreds of enzymatic reactions, while several B vitamins act as cofactors in pathways that convert food into usable cellular energy.

That does not mean that taking more of every nutrient creates more energy. A deficiency can impair normal physiology, so correcting it can make an enormous difference. Once requirements are met, however, increasingly high doses do not simply force cells to manufacture additional ATP.

This is why I prefer targeted correction of genuine deficiencies over enormous “energy” supplement stacks.

Protect your circadian rhythm

Human energy and alertness are not constant throughout the day. Our physiology follows circadian rhythms coordinated by the brain's central clock and clocks within peripheral tissues, and light is one of the strongest signals regulating this system.

Getting outdoor light after waking helps reinforce the biological distinction between day and night. Regular sleep and wake times, daytime physical activity and reducing excessive bright light late at night can also support circadian organisation. This matters because the circadian system influences far more than sleepiness. It interacts with metabolism, hormone secretion, body temperature and alertness.

If your days are spent indoors under artificial light and your nights staring into bright screens, your biology receives a rather confused message about what time it is. You do not need a circadian supplement. Start with daylight.

Build recovery into the system

Adaptation requires both stimulus and recovery. Exercise creates physiological stress; during recovery, the body repairs tissue and adapts to that challenge. The same principle applies more broadly. When every part of the day is demanding and recovery is consistently inadequate, it becomes harder to build physical capacity.

Sleep is the obvious foundation, but recovery also means allowing genuinely lower-demand periods between physical and psychological stressors. This becomes particularly important when increasing exercise. More training is not automatically better. The appropriate dose is the amount from which your body can recover and adapt.

What about mitochondrial supplements?

This is an area where marketing frequently gets ahead of physiology. Coenzyme Q10, creatine, magnesium, B vitamins, NAD-related products and numerous antioxidants are marketed as mitochondrial or energy supplements. Some have legitimate biological roles and some have evidence for particular populations or clinical situations, but that does not mean every tired woman after 45 needs them.

Creatine is particularly interesting because it supports rapid ATP regeneration through the phosphocreatine system and has evidence for supporting strength and lean mass when combined with resistance training, including in older adults. But even creatine does not replace sleep, adequate nutrition, physical training or treatment of an underlying medical problem.

Before spending hundreds on mitochondrial supplements, make sure the fundamental machinery has what it needs.

The energy-building hierarchy

If you want to rebuild energy after 45, the order matters. First, remove the drains: address disrupted sleep, iron deficiency, under-eating, excessive alcohol, overtraining or another identifiable problem. Then provide the raw materials: eat enough protein and overall energy, include appropriate carbohydrates and fats, and correct genuine nutrient deficiencies.

Next, build the machinery through regular walking, progressive resistance training and cardiovascular fitness. At the same time, protect sleep, circadian rhythm and recovery so your body can actually adapt to what you are asking it to do. If your energy still does not improve, investigate further rather than continuing to add supplements to unexplained fatigue.

You do not need seventeen energy hacks. You need to identify where the system is struggling and work from there.

Which biomarkers should you check to rebuild energy after 45?

If fatigue persists despite addressing the foundations, testing should be guided by symptoms and medical history. I commonly consider a full blood count and ferritin, with fuller iron studies when indicated; TSH and free T4 for thyroid function; fasting glucose and HbA1c, with fasting insulin where useful; and vitamin B12, folate and vitamin D according to symptoms and individual risk. Depending on the clinical picture, renal function, liver function and electrolytes may also be appropriate.

And remember what we established at the beginning of this series: if you are spending enough time in bed but consistently waking exhausted, particularly with snoring, gasping, morning headaches or significant daytime sleepiness, the investigation may need to involve sleep, not another blood test.

Your next step

At this point, you understand what fatigue can mean, where to start and how to rebuild the systems responsible for producing and using energy. There is one important piece left: what should we actually investigate when fatigue does not improve?

In the final article, we will look at the blood tests that can help uncover iron deficiency, anaemia, thyroid dysfunction, metabolic problems and nutrient deficiencies, what those results can tell us and, importantly, when normal blood tests mean we need to look somewhere else.

Next: Fatigue Blood Tests: What Is Actually Worth Checking?

You can also explore more articles, free and paid resources, my book and programmes in the Energy & Fatigue section of Feel Good Menopause.