Persistent tiredness (fatigue that survives a good night’s sleep and a quiet weekend) usually reflects change across oxygen transport, thyroid and metabolic pace, sleep, inflammatory load and nutrient absorption.
Tiredness won’t tell you which of these is behind it, and routine results often read as normal. A vivaINSIGHT test narrows it down. One at-home collection reads your gut microbiome, metabolites and lifestyle to show where your biology has drifted furthest from optimal.
Your first result is a baseline snapshot of your Biological Drift. Make a change, such as steadier meals or a regular bedtime, then test again to see whether your markers are moving the right way.
Persistent tiredness is a symptom, not a diagnosis. It tends to appear when several systems drift from their own baseline at once: most often iron status, thyroid function, glucose handling, inflammation and sleep quality. Some of these you can measure at home; others are GP blood tests.
Energy is not one thing. It is oxygen reaching tissue, fuel arriving steadily, mitochondria having what they need, and a nervous system that switches off at night when you rest.
Haemoglobin carries oxygen; iron builds haemoglobin and feeds the enzymes that generate cellular energy. Iron deficiency can be present without anaemia (haemoglobin inside the reference range while ferritin sits low), which is why fatigue is often missed on a standard full blood count.[1][2][3]
When insulin sensitivity falls, energy delivery can become less steady. In adults with insulin resistance, glucose fluctuations have been associated with poorer cognitive performance. Fasting insulin is a GP blood test; vivaINSIGHT reads your carbohydrate and energy metabolism.[5][10]
Hours in bed are not the same as restorative sleep. One week of restricted sleep reduced insulin sensitivity in healthy men, and irregular sleep timing is associated with poorer health outcomes independent of duration."wired but tired" pattern where you cannot get going and cannot switch off.[5][6]
Fatigue is one of the most consistently reported symptoms of low-grade systemic inflammation. Inflammatory signalling also suppresses iron availability, which is why hs-CRP is worth reading next to ferritin rather than on its own.[7][8]
Thyroid hormone sets the rate at which every cell works. Reduced function is a recognised cause of tiredness, cold intolerance and slowed thinking. TSH can drift toward the top of its reference range for years before anyone calls it abnormal.[4]
You absorb what your gut lets you absorb. Barrier integrity and microbial composition influence iron and B-vitamin uptake, and some gut bacteria synthesise B vitamins directly. Reduced diversity is also associated with higher inflammatory load, which closes the loop.[9]
Biological Drift is the gradual, usually invisible shift in your biology away from your own baseline over time.
Biological Drift usually happens inside normal reference ranges, which is why results can read as fine while you feel the change.
The systems are also linked: one week of short sleep lowers insulin sensitivity, and inflammatory signalling is one of the mechanisms studied in fatigue.[5][7]
One test shows where you are today. A subsequent test shows which way you are moving.
DRIFT TIMELINE
Biological Age50
76 / 100
81 / 100
64 / 100
70 / 100
64 / 100
WHAT YOU'D NOTICE
Tiredness becomes the default rather than the exception. You sleep the hours and wake unrestored. This is often when people ask for tests and are told everything is normal.
Illustrative direction of change drawn from published research, shown as vivaINSIGHT scores out of 100 against your own baseline. Not patient data, and not a prediction for any individual.
There is no single tiredness test, because tiredness is a symptom rather than a disease. Reading three layers together makes contributors visible as a pattern.
vivaINSIGHT is tri-layer: two lab-tested molecular layers (microbiome and metabolites) plus a structured lifestyle assessment, all from home.
Markers are scored against ideal ranges rather than the broad "not yet abnormal" reference band, then cross-referenced across layers. The pattern determines the sequence of actions.
All three layers captured on the same day, so the picture is internally consistent.
Our algorithms weight the markers furthest from optimal and read them across layers.
A nutrition plan and supplement recommendations tied to your markers, highest-leverage change first.
vivaBALANCE 360 tests in month 1, month 4 and month 10. Track the impact of your changes from test to test.
The systems behind this symptom change slowly and usually without obvious signs. Slow changes are often missed which is why testing and tracking over time is important.
Associations described in published literature. Testing identifies and tracks markers; it does not diagnose, treat, cure or prevent any disease.
One at-home collection. Three layers. A plan built on your own numbers. With vivaBALANCE 360 you test in month 1, month 4 and month 10, so you can see whether it worked.
Written by the vivaLAB science team. Clinically reviewed by Dr Andrew O'Brien, PhD, MBA, Executive Chairman, Co-Founder, vivaLAB. Last reviewed 28 September 2026. Next review March 2027.
Tiredness that is sudden, severe, or accompanied by unexplained weight loss, breathlessness at rest, chest pain or bleeding should be discussed with your GP promptly rather than investigated at home.
Persistent tiredness is usually multi-causal. The most commonly measured contributors are iron and oxygen transport, thyroid function, unstable glucose regulation, systemic inflammation, disrupted sleep and stress-axis signalling, and nutrient absorption. Because several can be present at once, testing across layers is more informative than a single blood test.
Your GP can test full blood count, ferritin and iron studies, vitamin B12 and folate, TSH with free T4, hs-CRP, HbA1c, fasting glucose and insulin, and vitamin D. vivaLAB does not collect blood; vivaINSIGHT adds your gut microbiome, metabolites and lifestyle, and reading them together is what makes the pattern visible.
Iron deficiency can be present without anaemia. Haemoglobin can sit inside the reference range while ferritin is low, and low iron stores affect oxygen transport and cellular energy production. Ferritin and transferrin saturation give a fuller picture than haemoglobin alone.
Thyroid hormone sets metabolic pace, and reduced thyroid function is a recognised cause of tiredness, cold intolerance and slowed thinking. TSH can drift toward the upper end of the reference range for years before it is flagged, which is why it is worth reading alongside inflammatory and nutrient markers rather than in isolation.
Biological drift is the gradual, usually invisible shift in your biology away from your own baseline over time. It usually happens inside normal reference ranges, which is why standard results can read as fine. One test gives you a baseline; a second shows the direction of change. Third and subsequent test allow you to forecast potential change.
Timeframes vary by person and by contributor. Iron stores in particular take months to rebuild. It's important to continue to test over this period and measure against your baseline.
No. vivaLAB's vivaINSIGHT Test uses at-home stool and urine collection: metagenomic sequencing of your gut microbiome (vivaBIOME), a urine-based assessment of cellular biochemistry (vivaMETABOLITE) and a lifestyle assessment. Blood markers and hormones are tests to discuss with your GP. vivaLAB is planning to introduce saliva and blood test options in the future.
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Every numbered claim on this page links to a record in PubMed, the US National Library of Medicine’s index of biomedical literature.
Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ, 2003. PMID 12763985
Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. 2018. PMID 29626044
Clinical evaluation of iron treatment efficiency among non-anemic but iron-deficient female blood donors: a randomized controlled trial. 2012. PMID 22272750
Hypothyroidism. 2017. PMID 28336049
Sleep restriction for 1 week reduces insulin sensitivity in healthy men. Diabetes, 2010. PMID 20585000
Sleep regularity is a stronger predictor of mortality risk than sleep duration: a prospective cohort study. Sleep, 2024. PMID 37738616
A systematic review of biological mechanisms of fatigue in chronic illness. 2018. PMID 29540066
Chronic fatigue syndrome and circulating cytokines: a systematic review. 2015. PMID 26148446
Short chain fatty acids: microbial metabolites for gut-brain axis signalling. 2022. PMID 35066114
Impact of blood glucose on cognitive function in insulin resistance: novel insights from ambulatory assessment. 2024. PMID 39261457
