Why You’re Tired All the Time — And What It Has to Do With Your Sex Life

There are few things more frustrating than feeling tired when you can’t quite explain why.

You slept. You had your coffee. You got through the day. And yet by evening, you feel like you’ve got nothing left in the tank.

Sometimes the reason is obvious. You didn’t sleep enough. You’ve been working too much. You’re under stress. You’ve been travelling or caring for someone or simply trying to keep up with everything life demands.

But sometimes fatigue becomes more persistent. You start noticing that the things that used to feel easy require more effort. Exercise feels harder. Concentration takes more work. You don’t have quite the same physical energy you used to.

And then there’s another change that people don’t always connect to the same problem:

Your sex drive isn’t quite what it used to be either.

It’s easy to treat these as completely separate issues. Fatigue belongs to the world of sleep, nutrition and general health. Libido belongs somewhere else entirely.

But sexual wellbeing is also a physical process. It involves the brain, nervous system, hormones, blood vessels, muscles and tissues—all of which require energy to function.

That brings us to something I find surprisingly fascinating:

the mitochondria inside your cells.

Mitochondria are often described as the “powerhouses” of our cells, which is a simplification—but a useful one.

Their best-known job is producing ATP, the molecule cells use to power many of their activities. Through a process called oxidative phosphorylation, mitochondria convert energy from the food we eat into a form our cells can use. But mitochondria do considerably more than produce energy. They are also involved in cellular signalling, calcium regulation, metabolism and the management of oxidative stress.¹

And here’s why that matters for how you feel.

Your body isn’t one big battery that gets switched on in the morning and gradually runs down throughout the day. Every cell is constantly carrying out processes that require energy. Your muscles need energy to contract. Your brain needs energy to maintain its signalling. Your heart needs energy to keep beating. Your cells need energy to repair themselves and maintain normal function.

So when we talk about “energy,” we’re talking about something much more fundamental than simply feeling sleepy.

We’re talking about cellular energy.

That doesn’t mean that feeling tired automatically means your mitochondria aren’t working properly. Fatigue is complicated, and there are countless possible contributors, including inadequate sleep, psychological stress, nutritional deficiencies, infections, medications, hormonal changes and chronic medical conditions.

But mitochondrial function is one part of the biology behind how our bodies produce and use energy—and researchers are increasingly interested in how mitochondrial function changes with ageing and across different stages of life.¹ ²

This is where the conversation becomes particularly interesting for women in their 40s and 50s.

Mitochondrial function changes with age, and mitochondrial dysfunction is considered one of the biological hallmarks associated with ageing. Researchers have also been studying the relationship between mitochondrial function and ovarian ageing.² ³

The ovaries are particularly interesting because oocytes contain exceptionally large numbers of mitochondria. Those mitochondria provide energy needed for processes including oocyte maturation and early embryonic development. Research suggests that age-related changes in mitochondrial function are associated with changes in oocyte quality, although the precise mechanisms are still being worked out.³ ⁴

This doesn’t mean that “bad mitochondria cause menopause.” They don’t.

Menopause is a complex biological transition involving changes in ovarian function, hormones and many other systems.

But it does show us something important: mitochondria aren’t just a niche topic in longevity research. They’re involved in fundamental aspects of reproductive and cellular biology.

And emerging research is beginning to look at mitochondrial function in the context of women’s health more broadly, including how sex hormones interact with mitochondrial biology. A recent review, for example, describes evidence that estrogen, progesterone and testosterone can influence mitochondrial processes including energy metabolism, oxidative phosphorylation and mitochondrial quality control.⁵

The science here is still developing, but it’s an interesting reminder that metabolism, hormones and cellular energy aren’t operating in separate compartments.

This is where I want to be careful.

There isn’t a simple scientific equation that says:

better mitochondria = higher libido.

And I wouldn’t trust anyone selling one.

Libido is influenced by an enormous number of factors. Hormones, relationships, stress, mental health, medications, sleep, pain, body image, physical health and sexual experiences can all play a role.

But sexual response itself is undeniably physical.

Arousal involves increased blood flow to genital tissues. Nerve pathways have to communicate between the brain and body. Pelvic muscles contract and relax. Vaginal tissues respond to hormonal and vascular changes. The brain is processing sensory information while coordinating a remarkably complex physiological response.

All of those processes require energy.

That doesn’t mean mitochondrial function determines whether you’re in the mood for sex. Desire is not an ATP problem.

What it does mean is that sexual wellbeing happens inside the same body that is managing everything else.

And when that body is chronically depleted, it isn’t unreasonable to ask whether your overall energy and wellbeing could be influencing how you experience sex.

Think about what happens when you’re exhausted.

You come home after a long day and the idea of cooking feels like work. Exercise gets pushed to tomorrow. You don’t want to socialise. You want to lie down and switch your brain off.

Sex can end up in the same category.

It’s not necessarily that you have suddenly stopped finding your partner attractive or that something is “wrong” with your libido. Sometimes you simply don’t have much physical or mental capacity left.

Research into female sexual dysfunction consistently points to the fact that sexual wellbeing is multifactorial. Fatigue, psychological distress, relationship factors, medications, hormonal changes and physical health can all influence sexual function.⁶

This is particularly relevant because women often experience several of these factors at once.

You may be sleeping badly because you’re stressed. You’re stressed because work is demanding. You’re exercising less because you’re tired. Your mood is affected because you’re not feeling like yourself. Your sex drive drops. Then you start worrying about your sex drive, which adds another layer of stress.

It becomes difficult to identify a single cause because there often isn’t one.

And that’s why I think the conversation around energy is more useful than simply asking, “How do I increase my libido?”

Sometimes the better question is:

“Why don’t I have the energy I used to?”

I’m not suggesting that a change in libido is a diagnostic test for mitochondrial dysfunction.

It isn’t.

But I do think changes in sexual wellbeing can sometimes be useful information about the broader state of your health.

If you’ve noticed that you’re more tired, less physically resilient, struggling to concentrate, sleeping poorly and also feeling less interested in sex, it’s worth looking at the whole picture rather than treating libido as an isolated problem.

That might mean asking about your sleep.

Looking at your stress levels.

Considering whether your diet is giving you enough energy and nutrients.

Thinking about how much you’re moving.

Reviewing medications.

Paying attention to hormonal changes.

And, if fatigue is persistent or significant, talking to a healthcare professional rather than assuming you simply need to “push through.”

Because fatigue isn’t a personality trait.

And neither is a low libido.

They’re signals worth paying attention to.

This is the most encouraging find.

Your mitochondria aren’t static.

They respond to the environment they’re in. Physical activity, nutrition, sleep and metabolic health can all influence mitochondrial function and adaptation. Exercise in particular is one of the most consistently studied ways of stimulating mitochondrial adaptations in skeletal muscle.⁷

That doesn’t mean you need to start taking a shelf full of “mitochondrial support” supplements.

In fact, I’d be sceptical of any product promising to “supercharge” your mitochondria.

The science is much less glamorous—and much more useful.

Your cells respond to the fundamentals.

Movement.

Adequate nutrition.

Sleep.

Recovery.

Metabolic health.

And managing the chronic stress that keeps your body in a constant state of demand.

Which brings us to the practical question:

What can we actually do to support healthy mitochondrial function—and potentially improve the foundations of our energy and wellbeing?

If mitochondria are involved in how our cells produce and use energy, the obvious question is: can we actually do anything to support them?

The answer is yes—but probably not in the way the wellness industry would have you believe.

There is no single food, supplement or morning routine that can suddenly “boost your mitochondria.” The strongest evidence points back to some of the least exciting things in health: regular physical activity, adequate nutrition, sufficient sleep and overall metabolic health. Exercise in particular produces adaptations across multiple tissues and metabolic systems, including changes in skeletal muscle mitochondrial function.¹³ ¹⁴

And honestly, I find that reassuring.

Because these aren’t glamorous interventions. They’re the things we’ve been told to do for decades. The difference is that we’re increasingly understanding some of the cellular biology behind why they matter.

If there is one lifestyle intervention with particularly strong evidence for mitochondrial adaptation, it’s exercise.

When you exercise, your muscles need more energy. In response, they adapt. Exercise training can increase mitochondrial content and alter mitochondrial respiratory function in skeletal muscle, making the muscle better equipped to meet energy demands.¹³ ¹⁴

You don’t need to become an endurance athlete for this to matter.

Walking, cycling, swimming, dancing, running and strength training all have different benefits. The important part is finding forms of movement you can actually sustain.

And there’s an interesting connection here to sexual wellbeing.

Exercise isn’t a treatment for low libido in the simplistic sense, but it can influence several of the systems involved in sexual function, including cardiovascular health, mood, physical fitness and blood flow. Research has found associations between physical activity and aspects of female sexual function, although the evidence base is still developing.¹⁵

A recent systematic review and meta-analysis also found that exercise interventions were associated with improvements across several domains of female sexual function, including desire, arousal, lubrication, orgasm and satisfaction. However, the authors noted that the overall certainty of evidence was low because of substantial variation between studies.¹⁶

So you don’t have to exercise because you’re trying to improve your sex life.

You can exercise because you’re supporting the systems that support almost everything else.

Your heart. Your muscles. Your brain. Your metabolism.

And potentially your sexual health too.

For women going through menopause, there is some additional evidence worth paying attention to. A systematic review of exercise interventions in peri- and postmenopausal women found some positive effects on sexual function, particularly from pelvic-floor and mind-body interventions, although results varied depending on the type of exercise.¹⁷

The takeaway isn’t that a particular workout will fix your libido.

It’s that movement is one of the few interventions that benefits so many of the biological systems involved in energy and sexual health at the same time.

This one gets overlooked in conversations about energy.

We’re surrounded by advice about eating less, cutting carbohydrates, fasting longer and controlling calories. Some of these approaches can be useful in specific circumstances, but there is a difference between creating a sustainable dietary pattern and chronically under-fuelling your body.

Your cells need energy and nutrients to function. Mitochondria don’t operate independently of the rest of your metabolism; they are part of a much larger system that depends on the availability and processing of nutrients.

That doesn’t mean you need a “mitochondrial diet.”

You don’t.

You need adequate energy, sufficient protein, a varied diet and enough essential vitamins and minerals to meet your body’s needs.

And this is where nutrition advice can become unnecessarily complicated.

If persistent fatigue is part of the picture, it’s much more useful to investigate whether there is an underlying reason for it than to immediately assume you need another supplement.

A deficiency. Poor sleep. An underlying medical condition. Medication effects. Chronic stress. Or something else that actually needs addressing.

We often talk about sleep as though it’s simply the time when you stop doing things.

Biologically, a lot is happening while you’re asleep.

Sleep is involved in metabolic regulation, brain function, immune processes and cellular maintenance. Emerging research is also exploring the relationship between sleep deprivation, oxidative stress and mitochondrial function. A recent review describes evidence linking insufficient sleep with impaired mitochondrial function and altered cellular energy production, although much of the mechanistic evidence comes from laboratory and disease models rather than studies of healthy humans.¹⁸

And if you’ve ever had several nights of poor sleep, you don’t need a scientific paper to tell you what that feels like.

You’re slower. Exercise feels harder. Concentration takes more effort. Your mood can change.

And sex may be one of the first things that gets pushed aside.

There is actually human research connecting these two things.

Research in women has found an association between poorer sleep quality and greater odds of female sexual dysfunction.¹⁹ Another study found that longer sleep duration was associated with greater next-day sexual desire and a greater likelihood of sexual activity, although the relationship between sleep and sexual function is complex.²⁰

That nuance matters.

So if you’re trying to understand why your energy—and perhaps your libido—has changed, sleep deserves more attention than it usually gets.

Not because getting eight hours will magically fix your sex life.

But because sleep is part of the biological foundation on which both energy and sexual wellbeing depend.

There is another piece of this conversation that is harder to quantify: chronic stress.

Acute stress is useful. Your body is designed to respond to a challenge by increasing alertness and mobilising energy.

The problem is when the stress response becomes your default setting.

Mitochondria aren’t just passive energy factories. They also participate in cellular signalling and stress responses, which is why researchers have become interested in the relationship between psychological stress and mitochondrial function.²¹

But this is an area where it’s particularly important not to overstate the evidence.

Research has identified links between psychological stress and changes in mitochondrial biology, but much of the mechanistic evidence remains preliminary and comes from experimental models. More research is needed to understand exactly how these processes translate into human health.²¹

So I wouldn’t tell you that a stressful month has somehow “damaged your mitochondria.”

The biology is considerably more complicated than that.

But it does reinforce something we already know from experience: chronic stress can affect how the body functions, and the effects aren’t confined to your mood.

And there’s a very practical consequence for sex.

When you’re constantly mentally “on,” relaxation becomes difficult. If your brain is still running through tomorrow’s meeting, your inbox, your finances or your family responsibilities, it can be difficult to shift into a state where pleasure feels accessible.

This isn’t about telling women to “relax more”—which is rarely helpful advice.

It’s about recognising that stress is a physiological state, not simply an emotion.

And sometimes creating space for pleasure is itself a way of stepping out of that state.

This is where I would exercise the most caution.

There are plenty of supplements marketed for mitochondrial health: CoQ10, NAD precursors, alpha-lipoic acid, PQQ, acetyl-L-carnitine and others.

Some have legitimate biological mechanisms behind them. Some have been studied in specific diseases or populations. A few have interesting early research.

But that’s very different from saying that everyone needs them.

CoQ10, for example, is involved in mitochondrial energy production and antioxidant processes. It is biologically plausible as a way of supporting energy metabolism, which is why it has been studied extensively.

But supplementation doesn’t automatically translate into more energy or better physical performance. The clinical evidence is mixed, and effects can vary substantially depending on the population and outcome being studied.²²

That’s a useful distinction.

A supplement can change a biological marker without necessarily producing a meaningful improvement in how you feel or function.

NAD is another fascinating area.

NAD is involved in redox reactions and energy metabolism, and researchers are investigating whether increasing NAD availability could have therapeutic applications.²³ But much of the excitement around NAD-boosting compounds comes from mechanistic, animal and early translational research.

That’s a long way from proving that taking an NAD supplement will give a healthy person more energy or a higher libido.

This is one of my favourite places to apply a simple rule:

Interesting science is not the same thing as a proven intervention.

If you’re considering a supplement because you’re persistently exhausted, it’s much more useful to first ask whether there’s an underlying reason for that fatigue.

A deficiency. A sleep disorder. A medication effect. A hormonal change. An infection. A metabolic condition.

Or something else that actually needs addressing.

Given how popular red light therapy has become, this is probably the point where someone will ask about it.

There is legitimate research into photobiomodulation and mitochondrial biology. Certain wavelengths of red or near-infrared light can interact with cellular components, and mitochondria—particularly cytochrome c oxidase—have been proposed as an important site of interaction. Researchers have investigated potential effects on mitochondrial signalling, cellular energy pathways and oxidative stress.²⁴

It’s an interesting field.

But once again, there’s a significant gap between “this has a plausible biological mechanism” and “this will improve your energy, slow ageing or increase your libido.”

The latter claims require clinical evidence.

So if you’re seeing a red-light device promising to “supercharge your mitochondria,” I’d treat that language with the same healthy scepticism I’d apply to any other wellness claim.

The science is interesting enough without making it bigger than it is.

The more I read about mitochondrial health, the less interested I become in the idea of “optimising” mitochondria.

Instead, I think about creating the conditions in which the body’s energy systems can function well.

Move regularly.

Build and maintain muscle.

Eat enough and eat a varied diet.

Get adequate protein and micronutrients.

Prioritise sleep.

Look after cardiovascular and metabolic health.

Find ways to manage chronic stress.

And investigate persistent fatigue rather than simply accepting it.

None of this is particularly revolutionary.

But perhaps that’s the point.

The body doesn’t necessarily need another hack.

It needs the fundamentals to work reasonably well, consistently, over time.

This brings us back to where we started.

If you’re exhausted all the time, it’s entirely understandable that sex might become less appealing.

That doesn’t mean your libido is broken.

It doesn’t necessarily mean your hormones are “off.”

And it certainly doesn’t mean you need to force yourself to be more sexual.

Sometimes the first step is simply understanding what your body is asking for.

Maybe it’s sleep.

Maybe it’s movement.

Maybe it’s better nutrition.

Maybe it’s addressing a health issue.

Maybe it’s managing stress.

Maybe it’s spending a little more time doing things that make you feel present in your body.

And sometimes, the answer will be much more specific and require medical attention.

The important thing is to stop thinking of sexual wellness as something that exists separately from the rest of your health.

Your ability to experience pleasure is happening inside the same body that is carrying you through your workday, processing stress, regulating hormones, maintaining muscle and producing energy.

That’s why I find the mitochondria conversation so interesting.

Not because I think we should all start obsessing over our mitochondria.

But because it gives us another way of understanding something we’ve all experienced:

When your body has no energy left, it’s hard to feel fully alive in any part of it—including your sex life.

And perhaps the most useful takeaway isn’t to find a way to “boost” your cellular energy.

It’s to start asking why yours feels depleted in the first place.

Because sometimes, the best thing you can do for your sex life has very little to do with sex.

It starts with taking better care of the body that experiences it.

Share

¹. Hawley JA, et al. Integrative biology of exercise. Cell. 2021;184(5):1285–1303.

². Hood DA, Memme JM, Oliveira AN, Triolo M. Maintenance of skeletal muscle mitochondria in health, exercise, and aging. Annual Review of Physiology. 2019;81:19–41.

³. Granata C, Jamnick NA, Bishop DJ. Training-induced changes in mitochondrial content and respiratory function in human skeletal muscle. Sports Medicine. 2018;48:1809–1828.

⁴. Stanton AM, Handy AB, Meston CM. Sexual function in women with exercise and physical activity. Relevant clinical literature on exercise and female sexual function.

⁵. Silveira AB, et al. Physical activity and exercise for erectile dysfunction: systematic review and meta-analysis. Journal of Sexual Medicine.

⁶. NIH Office of Dietary Supplements. Dietary Supplement Fact Sheets. Information on micronutrients involved in energy metabolism, including B vitamins, iron and magnesium.

⁷. Zhao M, Abbasi AA, Li P, Lu P. Mitochondrial dysfunction in sleep deprivation. Metabolic Brain Disease. 2026;41(1):90. doi:10.1007/s11011-026-01853-5.

⁸. Martínez Vázquez S, Hernández Martínez A, Peinado Molina RA, Martínez Galiano JM. Association between sexual function in women and sleep quality. Frontiers in Medicine. 2023;10:1196540. doi:10.3389/fmed.2023.1196540. PMID: 37636576; PMCID: PMC10457145.

⁹. Picard M, McEwen BS. Psychological stress and mitochondria: a conceptual framework. Psychosomatic Medicine. 2018;80(2):126–140.

¹⁰. Hernández-Camacho JD, et al. Coenzyme Q10 supplementation in aging and disease. Frontiers in Physiology. 2018;9:44.

¹¹. Rajman L, Chwalek K, Sinclair DA. Therapeutic potential of NAD-boosting molecules: the in vivo evidence. Cell Metabolism. 2018;27(3):529–547.

¹². Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophysics. 2017;4(3):337–361.

¹³. Hawley JA, Hargreaves M, Joyner MJ, Zierath JR. Integrative biology of exercise. Cell. 2014;159(4):738–749. doi:10.1016/j.cell.2014.10.029.

¹⁴. Lundby C, Jacobs RA. Adaptations of skeletal muscle mitochondria to exercise training. Experimental Physiology. 2016;101(1):17–22. doi:10.1113/EP085319.

¹⁵. Stanton AM, Handy AB, Meston CM. The Effects of Exercise on Sexual Function in Women. Sexual Medicine Reviews. 2018;6(4):548–557. doi:10.1016/j.sxmr.2018.02.004.

¹⁶. Ruiz-Pérez I, Ruiz-Rios M, et al. Systematic review and meta-analysis on the beneficial effect of exercise on sexual dysfunction in women. Journal of Sexual Medicine. 2026.

¹⁷. Cabral PU, et al. Effects of Physical Exercise on Sexual Function and Quality of Sexual Life Related to Menopausal Symptoms in Peri- and Postmenopausal Women: A Systematic Review. International Journal of Environmental Research and Public Health. 2020;17(8):2680. doi:10.3390/ijerph17082680.

¹⁸. Zhao M, Abbasi AA, Li P, Lu P. Mitochondrial dysfunction in sleep deprivation. Metabolic Brain Disease. 2026;41(1):90. doi:10.1007/s11011-026-01853-5.

¹⁹. Kling JM, Kapoor E, Mara K, Faubion SS. Associations of sleep and female sexual function: good sleep quality matters. Menopause. 2021;28(6):619–625. doi:10.1097/GME.0000000000001744.

²⁰. Kalmbach DA, Arnedt JT, Pillai V, Ciesla JA. The impact of sleep on female sexual response and behavior: a pilot study. Journal of Sexual Medicine. 2015;12(5):1221–1232. doi:10.1111/jsm.12858.

²¹. Picard M, McEwen BS. Psychological Stress and Mitochondria: A Systematic Review. Psychosomatic Medicine. 2018;80(2):141–153. doi:10.1097/PSY.0000000000000545.

²². Deng H, Song T, Yin M, et al. Coenzyme Q10 supplementation increases blood concentrations but shows limited and inconsistent effects on exercise performance: a systematic review and meta-analysis. British Journal of Nutrition. 2025. doi:10.1017/S0007114525106211.

²³. Rajman L, Chwalek K, Sinclair DA. Therapeutic Potential of NAD-Boosting Molecules: The In Vivo Evidence. Cell Metabolism. 2018;27(3):529–547. doi:10.1016/j.cmet.2018.02.011.

²⁴. Hamblin MR. Mechanisms and Mitochondrial Redox Signaling in Photobiomodulation. Photochemistry and Photobiology. 2018;94(2):199–212. doi:10.1111/php.12864.