Fatigue: What Causes It And How Do You Get Your Energy Back?
Feeling constantly tired has become an everyday experience for many people. It can show up in different ways, from a general sense of low energy to an overwhelming exhaustion that disrupts daily life. In fact, fatigue is one of the most common reasons people seek medical advice. But what’s behind this growing sense of tiredness?
In this article, we’ll take a closer look at some of the factors that can sap our energy. From sleep habits and nutrition to hormonal changes, underlying health issues, and even environmental factors such as mold, there are many possible contributors. Understanding what’s at the root of your fatigue can be the first step toward feeling better.
What Causes Fatigue?
Fatigue isn’t the same for everyone, so the first step is to understand what it feels like for you. Did your tiredness creep in gradually, or did it follow an illness such as COVID-19? Does it feel like a mild, day-to-day weariness where you have to push yourself through tasks? Or is it a deep, bone-level exhaustion that threatens your ability to work or care for yourself? Some people even experience extreme fatigue that makes exercise or simple activities impossible without hours or days of recovery.
When your mind and body aren’t functioning as they should, it’s important to work with a qualified health professional. If you’re ordering lab tests or trying nutritional supplements on your own, be sure to share those results with your provider so they can see the full picture.
In some cases, it can be helpful to consult a functional medicine physician. Traditional medical settings are often designed to rule out a limited range of conditions and may not leave much time for exploring more complex or less obvious causes of fatigue. Functional practitioners typically look more broadly, which can be valuable if fatigue is your main concern.
Because tiredness can arise from many different factors, your healthcare provider may consider a wide range of possibilities, including:
Poor Sleep
High-Stress Lifestyle
History of Critical Illness or COVID-19
Heavy Metal Toxicity
Nutritional Deficiencies
Chronic Fatigue Syndrome or Fibromyalgia
Thyroid Dysfunction
Mold Toxicity
Identifying which factors are affecting you can be the first step toward regaining your energy and improving your quality of life.
Sleep And Fatigue
There are several issues that need to be ruled out or treated:
Sleep Apnea: Have someone watch you while you sleep to find out if you stop breathing while you sleep. It is very common to have sleep apnea cause disruptions in deep sleep without ever being aware that you are waking continuously overnight. It is particularly common for those carrying extra weight, and facial bone structure also plays a large part.
Caffeine: Caffeine can stay in your system much longer than many people realize. Even 12 hours after a cup of coffee, roughly a quarter of the caffeine you consumed may still be active in your body. This lingering effect can interfere with deep, restorative sleep, leaving you less refreshed the next day and potentially creating a cycle of tiredness and more caffeine use. [PMC6230475]
Alcohol: Alcohol has its own impact on sleep. While it may initially feel calming, it disrupts REM sleep, the stage associated with dreaming and mental restoration. Once the sedative effect wears off, your nervous system can rebound with increased activity, which further disturbs sleep quality. [PMC4666864]
Daily Stress and Chronic Fatigue
We are living especially stressful lives in the modern world. When stress is chronic, it can cause disruption in the circadian rhythm and adrenal hormones. The result is low cortisol in the morning when it should be high to wake us up and get us moving followed by high cortisol at night that leaves us too stressed to fall asleep.
Testing For Cortisol Levels
A Salivary Cortisol Test (affiliate link) can help you and your physician decide if this type of stress hormone disruption is involved in your fatigue symptoms. This lab can be ordered in the NutriScape Lab Shop.
Nutritional Deficiencies That Cause Fatigue
Deficiencies of B12 and Iron immediately come to mind as classic causes of fatigue. However, many vitamin and mineral deficiencies can be responsible for generalized fatigue. Many times the specific deficiency can’t be identified because there are no reliable or affordable tests available. We’ll list these energy-related nutrients along with affiliate links to lab testing when available:
Here is a list of nutritional deficiencies that can cause fatigue:
Iron deficiency (anemia): Clinicians sometimes reference that fatigue may be present with ferritin levels below about 50, but ask your physician about this because iron supplementation is thought to increase the risk of certain other health problems.
Vitamin B12 deficiency: Clinicians often reference that fatigue can be a problem if levels drop below 550 –/ml.
Tests for various nutrient deficiencies and many other nutrition-related problems can be ordered online through the NutriScape Lab Shop (affiliate link).
Testing For Anemia
The Anemia Panel (affiliate link) from Access Medical Labs tests for Ferritin, Total Iron Binding Capacity, Iron, Folate, B12, and Reticulocyte Count.
Testing For Vitamin D Deficiency
Vitamin D dosages should be adjusted based on your blood level with many clinicians recommending an optimal Vitamin D level of 50-80 ng/ml. Vitamin D Labs (affiliate link) can be ordered in the NutriScape Lab Shop.
Comprehensive Nutritional Testing
Comprehensive nutrient testing is an option for those who want to know their status for almost ALL of the nutrients that can cause fatigue. These tests are often not covered by health insurance but can be covered by health savings accounts. There are many good tests out there, many of which require a good deal of clinical skill to appropriately interpret. The clarity of the reports for the NutrEval FMV and Metabolomix+ tests below set them apart.
NutrEval FMV Comprehensive Nutrient Metabolism Testing (affiliate link) gives exquisite insight into your nutritional status, oxidative stress, and detoxification ability. It covers testing for Antioxidants, B Vitamins, Digestive Support, Essential Fatty Acids, Minerals, Metabolic Analysis Profile, Amino Acids Analysis, Essential & Metabolic Fatty Acids Analysis, Elemental Analysis, and Oxidative Stress. An excellent report is generated that can help guide treatment of any concerns brought out by the test.
Genova Diagnostics also offers the Metabolomix+ (affiliate link), which is a urine test. It differs slightly from the NutrEval, in that it does not provide information on omega balance. Please note that the report you receive will not have the omega balance section shown in the sample report will not be included in the test.
History of Critical Illness
After a serious illness, many people face a long and often frustrating recovery marked by deep, lingering fatigue. This exhaustion is not simply about “feeling tired.” It is closely tied to the body’s inflammatory response and the way critical illness disrupts normal cellular metabolism. When the body is fighting a major infection or injury, it releases large amounts of cytokines and other inflammatory molecules. While these substances are essential for healing, they can also damage cells and throw normal energy production off balance. [PMID: 34363641]
During this heightened state of inflammation, the body needs enormous amounts of energy, but its ability to produce that energy is often reduced. The tiny powerhouses inside cells, the mitochondria, can become damaged and less able to generate adenosine triphosphate (ATP), the molecule that fuels nearly every process in the body. The result is a mismatch between what the body demands and what it can deliver.
Critical illness also alters how the body handles nutrients. Insulin resistance can develop, protein stores are broken down to supply energy, and lean body mass may be lost. This combination of factors intensifies weakness and fatigue.
Because so much attention in critical care is focused on lifesaving technologies and medications, the role of nutrition in recovery can sometimes be overlooked. Yet simple, targeted nutrient support aimed at calming inflammation and supporting cellular metabolism can make a real difference.
Supplements containing antioxidants, omega-3 fatty acids, and amino acids such as arginine and glutamine may help modulate inflammation and support mitochondrial repair. Vitamins and minerals that act as essential cofactors in energy-producing reactions, like B vitamins, magnesium, and coenzyme Q10, can also play an important role in restoring healthy metabolism. By addressing these underlying disturbances, targeted nutrition can help reduce post-illness fatigue and support a more complete recovery, improving both strength and quality of life after a critical illness.
Post-COVID Fatigue
Long COVID patients frequently report persistent fatigue, a condition that has puzzled scientists and doctors alike. To understand this, several theories have been put forward, each looking at different aspects of the body’s response to the initial infection and its aftermath.
One prominent theory focuses on the immune system’s continued activation. Even after the virus is no longer detectable, the immune system may still act as if it’s fighting off an invader. This state of heightened alert can lead to systemic inflammation, a condition known to cause profound tiredness and exhaustion. Essentially, the body’s defense mechanisms, which are designed to protect against illness, may inadvertently contribute to the sensation of fatigue by overworking the system. [PMC9403611]
Another area of interest is the impact of COVID-19 on mitochondria, the components within cells responsible for generating energy. If the virus damages these mitochondria, it could lead to a significant decrease in energy production, leaving patients feeling constantly drained. This theory suggests that the virus might cause long-term changes to cellular structures, affecting their ability to function normally.
The autonomic nervous system, which regulates involuntary functions such as heart rate and blood pressure, might also be disrupted. This dysregulation can affect energy management within the body, making it difficult for patients to maintain stable energy levels. Symptoms such as rapid heartbeat, dizziness, and fluctuations in blood pressure can all contribute to the overall feeling of fatigue.
Moreover, the possibility of dormant viruses becoming reactivated due to the body’s weakened state post-COVID-19 adds another layer of complexity. These latent viruses can place additional stress on the immune system, further depleting the body’s energy reserves.
Lung damage, a common complication in more severe COVID-19 cases, can lead to persistent hypoxia, where the body’s tissues do not receive enough oxygen. This lack of oxygen can significantly impact the body’s energy levels, as oxygen is crucial for energy production in cells.
Psychological factors play a significant role as well. The experience of going through a severe illness like COVID-19 can lead to stress, anxiety, and depression, all of which can exacerbate physical symptoms of fatigue. The mental toll of recovering from such a condition, along with the social and economic impacts, can contribute to the persistent tiredness reported by long COVID patients.
Heavy metals, such as lead, mercury, arsenic, and cadmium, can enter the body through contaminated food, water, industrial exposure, or even certain medications and supplements. Once inside the body, these toxic elements can disrupt biochemical and physiological processes, leading to a range of health issues, including fatigue. [NBK560920]
One reason heavy metals may contribute to fatigue is their ability to interfere with mitochondrial function. Mitochondria are the cell’s powerhouses, responsible for producing energy in the form of ATP (adenosine triphosphate). Heavy metals can damage mitochondrial DNA and impair the enzymes involved in energy production, leading to decreased energy output which causes fatigue.
Heavy metals can also disrupt the balance of essential minerals in the body by competing for absorption sites and interfering with their biological functions. For example, lead can displace calcium, affecting muscle and nerve function. Cadmium can interfere with zinc, which is a crucial element for immune system health and other metabolic processes. This disruption in mineral balance can further contribute to a feeling of tiredness and lack of energy.
Heavy metals also have a profound impact on the immune system. They can trigger an inflammatory response, leading to chronic inflammation, which is energetically demanding and can deplete the body’s resources, causing fatigue. Furthermore, the immune system’s attempt to fight off the toxic effects of heavy metals can divert energy away from other functions, exacerbating the feeling of tiredness.
Moreover, the neurological effects of heavy metal toxicity, including cognitive impairment and mood disturbances, can also contribute to the sensation of fatigue. These metals can affect neurotransmitter synthesis and function, leading to changes in sleep patterns, anxiety, and depression, all of which are closely linked to increased fatigue.
Testing For Heavy Metals
In the NutriScape Lab Shop, Access Medical Labs offers the Heavy Metals, 21 Toxic, Urine (24-hour) (affiliate link). This test measures the levels of 21 different toxic metals in your urine. It can help identify if you have been exposed to heavy metals that might be causing your fatigue.
Thyroid-Related Fatigue: Hypothyroidism and Hashimoto’s Thyroiditis
The thyroid gland plays a crucial role in regulating the body’s metabolism through the production of thyroid hormones. When it doesn’t produce enough of these hormones, a condition known as hypothyroidism, people experience significant fatigue among other symptoms. This type of fatigue is not just the typical tiredness felt after a long day; it can be a profound lack of energy that can severely impact daily functioning and quality of life. Symptoms of hypothyroidism also include weight gain, cold intolerance, dry skin, hair loss, constipation, depression, slowed heart rate, and muscle weakness.
Incidence of Hypothyroidism
In the United States, it’s estimated that about 4.6% of the population has hypothyroidism, being more common in women and older adults. [PMC6822815] However, the incidence of undiagnosed hypothyroidism is also significant. Studies suggest that up to 60% of those with thyroid disease don’t know they have it.
Hashimoto’s Thyroiditis and Hypothyroidism
A vast majority of people with hypothyroidism, probably 80-90%, are caused by Hashimoto’s thyroiditis, an autoimmune disorder where the immune system attacks the thyroid gland. This attack leads to inflammation and damage to the thyroid, gradually impairing its ability to produce hormones. The progression of Hashimoto’s can vary; some people may experience periods of thyrotoxicosis (higher than normal thyroid hormone levels) early in the disease, but most will eventually develop hypothyroidism as the gland’s function continues to decline.
Diagnosing hypothyroidism involves evaluating symptoms and conducting blood tests to measure levels of Thyroid Stimulating Hormone (TSH) and thyroxine. TSH levels are usually elevated in hypothyroidism as the pituitary gland tries to stimulate more hormone production from the thyroid. Many physicians rely on TSH alone to screen for thyroid dysfunction with the rationale that this is all they need in order to decide on a prescription. This can be problematic because TSH only tells how much the pituitary gland is signaling the thyroid to work. A person can have normal TSH levels but still have symptoms due to abnormal levels of Free T4 or Free T3.
Measuring thyroid antibody levels offers more insight into the autoimmune drivers of thyroid function. Free Thyroxine (T4) and Free Triiodothyronine (T3) levels provide insight into the actual hormones available for the body’s use. Thyroglobulin Antibodies (TgAb) and Thyroid Peroxidase Antibodies (TPOAb) tests are essential for identifying autoimmune thyroid disease (Hashimoto’s thyroiditis) where the immune system mistakenly attacks the thyroid gland. These antibodies can be present even before the TSH level becomes abnormal, allowing for earlier intervention.
Also, measuring Total T4 and Total T3 can help in understanding the overall thyroid hormone production, but these tests include both bound and free hormones, with only the free hormones being biologically active. Together, these tests offer a more nuanced view of thyroid function and autoimmune activity. Knowing about the autoimmune activity in your body can allow you to begin appropriate treatment like a gluten-free diet which can help slow down the progression of this and possibly other autoimmune diseases. Read more about hypothyroid in our article: Thyroid Support: Top Supplements You Should Know About.
Labs For Thyroid Function
In the NutriScape Lab Shop, BostonHeart Diagnostics offers a Thyroid Panel (affiliate link) that includes Free and total T4, Free and total T3, Thyroglobulin Antibodies, Thyroid Peroxidase Antibodies, and TSH.
For those who have also been having difficulty with weight gain, ZRT Laboratory offers the Weight Management + Thyroid, which includes Vitamin D, Cortisol, DHEA-S, Estradiol, Fasting Insulin, Free T4, Free T3, Hemoglobin A1C, Progesterone/E2 Ratio, Progesterone, Testosterone, Thyroid Peroxidase Antibodies, TSH.
If it turns out any of these numbers are out of range, you’ll want to share them right away with your physician. Since thyroid labs are so involved, you may want to check out the book by Datis Karrazian titled, “Why Do I Still Have Thyroid Symptoms? When My Lab Tests Are Normal”. (Affiliate link)
Chronic Fatigue Syndrome or Fibromyalgia
One of the biggest problems for people with chronic fatigue syndrome and fibromyalgia has been the inability to prove that there is anything wrong. For many years, physicians assigned chronic fatigue symptoms to psychological causes and sent CFS patients to psychiatrists. In 2016, research was published describing lab markers for CFS that are about 95% reliable. [PMC5027464] Unfortunately, these are not a part of the labs that are normally available through your physician.
How CFS Might Begin
Researchers have been trying for some time to figure out how CFS begins and a model has been presented to understand chronic fatigue syndrome (CFS). This model suggests that harmful molecules produced after an infection can cause long-term inflammation and stress, especially in individuals already genetically susceptible to these responses.
This ongoing inflammation and stress can lead to a series of problems. One issue is an increase in gut permeability, which allows normally beneficial gut bacteria to move into the bloodstream. This can disturb the nervous system, resulting in brain inflammation and changes in brain function.
In response to these stress levels, the body may slow down certain immune and metabolic processes. The impact of this response could be weaker mitochondria (cellular power generators), a less responsive immune system, and cells entering a sort of ‘sleep’ mode. The model also includes a process known as endotoxin tolerance, which occurs when the body’s cells stop responding to certain bacterial toxins.
Finally, the model suggests that the immune and metabolic abnormalities seen in CFS could be explained by this concept of endotoxin tolerance. [PMC6428797]
Mold Toxicity As A Cause of Extreme Fatigue
Molds can thrive in damp and poorly ventilated environments and release spores and mycotoxins into the air. These substances can be inhaled or come into contact with the skin, leading to a range of health problems, including allergic reactions, respiratory issues, and neurological symptoms and profound fatigue.
A particularly concerning aspect of mold exposure is the genetic susceptibility that makes about a quarter of the population more vulnerable to its adverse effects. Research indicates that approximately 25% [*] of people have a genetic predisposition that impairs their ability to effectively eliminate mycotoxins from their bodies. This genetic variation affects the immune system’s response to mold, leading to a chronic inflammatory state causes fatigue. People with this susceptibility may experience more severe and persistent symptoms when exposed to mold, including heightened fatigue, cognitive difficulties, and a range of systemic issues.
Some publicatiovehemently insist that mold toxicity does not exist because there are no consistent biomarkers or disease definition. [PMID: 28299723] These physicians will likely send their patients to psychiatrists for treatment as has so often been the case in the past with fibromyalgia and other physical diseases without biomarkers. However, for those who have been working with patients thought to have mold toxicity many solid theories are proposed [*] for mechanisms by which mold can cause disease. [PMC8619365]
The relationship between mold exposure and chronic fatigue underscores the importance of environmental health in our overall well-being. For those genetically predisposed to mold sensitivity, exposure can trigger an immune response that leads to chronic inflammation and oxidative stress, mechanisms closely linked to the development of fatigue. This inflammation can disrupt the body’s energy production processes and hormonal balance, further contributing to the sensation of exhaustion.
Addressing mold exposure, especially for those with genetic susceptibility, involves identifying and eliminating mold sources in living and working environments. It also highlights the need for increased awareness and testing for mold sensitivity, particularly for individuals experiencing unexplained chronic fatigue. By acknowledging the role of mold and genetic factors in health, we can better understand and address the multifaceted nature of chronic fatigue, paving the way for more targeted and effective interventions.
A study looked at patients diagnosed with chronic fatigue syndrome (CFS) who were evaluated for the presence of mold toxins in their urine. They found that 93% out of 112 patients tested positive for at least one mycotoxin. More than 90% of these patients had been exposed to water damaged buildings. [PMC3705282]
Testing For Mold Toxicity
In the NutriScape Lab Shop, there are two urine tests for mycotoxins. There are probably countless other mycotoxins that could cause issues that have not yet been discovered.
The MycoTOX (affiliate link) from Mosaic Diagnostics tests for:
Fatigue that sticks around despite lifestyle changes and medical checks can leave people feeling stuck and frustrated. One often-overlooked answer is undermethylation, a subtle metabolic pattern that can quietly drain energy lower mood and reduce stress resilience. The article Undermethylation: A Little‑Recognized Driver of Longstanding Fatigue explains how this biochemical issue can hide in plain sight, why lab testing matters, and how careful supplement support with nutrients like TMG, methionine, and key cofactors can help restore balance. Some common signs that may point to undermethylation include:
Chronic fatigue that doesn’t improve with rest
Low motivation or persistent low mood
High histamine symptoms (congestion, hives, allergies)
Obsessive or perfectionistic thinking
High functioning
Sensitivity to stress or poor stress recovery
Often begins in the teen years
Often improves with SSRIs
Ironically, while methylated B vitamins are often recommended to support methylation, they can sometimes make symptoms worse for people who are truly undermethylated. This can happen if used in high doses of methylated folate is used without testing. Understanding these patterns helps people get to the root of fatigue and avoid feeling worse from well‑meaning guesswork.
Food First!
Although this article discusses supplements in detail, don’t forget that we are absolutely committed to the “Food First” approach to nutrition. When it comes to your health, the totality of your eating habits far surpasses the impact of individual nutrients or any single supplement you consume. Even though this article doesn’t delve into the broader picture of your overall diet, it’s crucial to keep this element at the forefront of our minds. Food is one of the “Pillars of Health”. Your food needs to provide all the vitamins, minerals, fiber, and phytochemicals to nourish your body systems down to the cellular level.
Food choices, rather than supplements, are the most critical factors for a healthy gut microbiome. These trillions of tiny inhabitants in your gut affect your brain waves; they orchestrate your immune system. They possess the power to create molecules that can switch genes on or off and are even capable of synthesizing neurotransmitters. Opting for organic foods and steering clear of plastic packaging (including those labeled BPA-free) is a smart move to limit toxin exposure. The sum of all these parts leads to a powerful conclusion: the ultimate key to your health lies in the quality and balance of the food you consume. Supplements are secondary.
To Sum It Up
Solving fatigue means getting a handle on what might be causing it. For this, you will need to be working with a functional physician who can help with nailing down the diagnosis. Fatigue can be caused by anything from sleep disorders and nutritional deficiencies to chronic infections, hormonal imbalances, and environmental factors like mold exposure. It is signal that tells us something is amiss. The genetic predisposition of a significant portion of the population to certain conditions, such as mold sensitivity, adds another layer of complexity, highlighting the importance of personalized approaches in both diagnosis and treatment.
Recognizing the broad range of potential causes is crucial for effectively addressing fatigue. It encourages a comprehensive evaluation of an person’s lifestyle, environment, and health status. As scientists continue to explore the intricacies of fatigue, it becomes increasingly clear that its resolution lies in understanding the unique interplay of factors affecting each person, requiring holistic and patient-centered care in the journey toward wellness.
This Article is Not a Substitute for Medical Advice
This information is provided for educational purposes only and is not a substitute for medical advice. Supplement Sciences does not provide medical care and cannot ensure the safety or effectiveness of any product for your personal use. Always consult your physician before starting any supplement, especially if you are pregnant, breastfeeding, or managing a serious health condition such as cancer, liver disease, or kidney disease. Dietary supplements are not designed to diagnose, treat, cure, or prevent any disease.
* These statements have not been evaluated by the Food and Drug Administration.
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