Melatonin Test

Your body runs on a 24-hour clock, and melatonin is the signal that keeps it synchronized. Every night, a tiny gland deep in your brain begins releasing this hormone into your bloodstream as darkness falls, telling your cells it is time to shift into repair, recovery, and sleep mode. When that signal weakens or shifts out of rhythm, the consequences reach far beyond a bad night's rest.

A blood melatonin test captures a snapshot of this nightly surge. Because melatonin (N-acetyl-5-methoxytryptamine) follows a dramatic daily cycle, with levels climbing after dark, peaking between 2 and 4 AM, and dropping back to near zero during daylight, when your blood is drawn matters as much as what the number says. This test can reveal whether your circadian signal is strong, blunted, or mistimed, giving you a window into a system that influences everything from sleep quality to metabolic health and cancer risk.

How Melatonin Works

Melatonin is built from tryptophan, the same amino acid found in protein-rich foods. In the pineal gland, a pea-sized structure near the center of the brain, tryptophan is first converted to serotonin, then to melatonin through a chain of four chemical reactions. The slowest and most controlling step in this process, governed by an enzyme called AANAT, is switched on by darkness and switched off by light. This is why even brief bright light exposure at night can suppress melatonin production within minutes.

Once released, melatonin acts through two types of receptors (MT1 and MT2) found throughout the body, from the brain's master clock (the suprachiasmatic nucleus) to the heart, pancreas, immune cells, and bones. It also works independently of receptors as a direct antioxidant, neutralizing damaging molecules called free radicals, particularly inside mitochondria, the energy-producing compartments of your cells.

The pineal gland produces only about 5% of total melatonin in the body. The rest is made locally in tissues like the gut, retina, immune cells, and liver, where it acts as an on-site protector rather than a circulating hormone. This locally produced melatonin does not enter the bloodstream and does not follow a day-night rhythm, which means a blood test specifically reflects the pineal gland's circadian output.

The Age-Related Decline

Melatonin production peaks in early childhood and declines steadily from there. In children aged 1 to 3, nighttime levels average around 325 to 330 pg/mL. By the late teens, that number drops to roughly 63 pg/mL. Young adults typically peak around 100 pg/mL at night, and by ages 70 to 90, nighttime levels average just 29 to 35 pg/mL. Daytime levels remain consistently low across all ages, typically below 10 pg/mL.

This progressive decline contributes to the circadian disruption, sleep fragmentation, and increased inflammation that characterize aging. Whether maintaining higher melatonin levels through supplementation can slow these processes remains an active area of research, but the association between low melatonin and accelerated aging biology is consistent across multiple studies.

Type 2 Diabetes Risk

The link between melatonin and blood sugar regulation is one of the most studied connections. People with type 2 diabetes consistently show lower nighttime melatonin levels than those without the disease. In a prospective study, individuals with the lowest melatonin secretion were about 50% more likely to develop type 2 diabetes over follow-up (HR 1.51 for the lowest versus the combined second through fifth quintiles), even after adjusting for other risk factors.

Genetic variants in melatonin receptors also increase diabetes risk, reinforcing the idea that this is a causal pathway, not just an association. Meta-analyses of randomized trials in people with existing type 2 diabetes show that melatonin supplementation lowers fasting blood glucose by about 4.6 to 12.7 mg/dL and reduces fasting insulin by roughly 2.3 µIU/mL, with the strongest effects seen at doses above 6 mg/day taken for more than 12 weeks.

One important nuance: immediate-release melatonin taken at the wrong time can actually impair glucose tolerance in the short term. This means the timing and formulation of melatonin supplementation matter for metabolic effects, and a blood test showing your baseline level can help guide whether and how supplementation makes sense.

Cardiovascular Disease

Reduced melatonin levels are consistently found in people with metabolic syndrome and cardiovascular disease. However, the largest prospective study to date, pooling over 159,000 U.S. adults followed for up to 23 years, found that regular melatonin supplement use was not significantly associated with cardiovascular disease risk in the general population (HR 0.94, 95% CI 0.83 to 1.06).

An intriguing exception appeared in women with more than five years of rotating night shift work. In that subgroup, melatonin supplement use appeared to attenuate the elevated cardiovascular risk associated with shift work (interaction p = 0.013), though the individual subgroup comparison did not reach statistical significance on its own (HR 0.91, 95% CI 0.67 to 1.24). This suggests melatonin supplementation may be most protective when the circadian system is under the greatest stress, but the finding needs confirmation.

Cancer Associations

Epidemiological studies consistently link lower melatonin levels and circadian disruption (especially from night shift work) to higher cancer risk, particularly for breast and prostate cancer. A separate Japanese cohort study of over 29,000 adults found that the highest dietary melatonin intake was associated with 10% lower total mortality and 15% lower cardiovascular mortality over 16 years.

When melatonin is added to standard cancer treatment, some randomized trials report improved 1-year survival (roughly twice as likely to survive compared to standard treatment alone, though this evidence comes largely from a single research group and is rated low certainty). A Cochrane review concluded that melatonin may have little to no effect on quality of life in cancer, and that survival data need confirmation from independent trials before drawing firm conclusions.

Sleep and Circadian Rhythm Disorders

Melatonin is the gold-standard biomarker for assessing circadian phase. The dim light melatonin onset, or DLMO, which marks the time your melatonin begins rising in the evening, has a sensitivity of 90.3% and specificity of 84.0% for diagnosing delayed sleep phase syndrome. This makes it more accurate than sleep diaries or questionnaires for distinguishing true circadian misalignment from behavioral sleep problems.

Only about 57% of people clinically diagnosed with delayed sleep phase disorder actually show a delayed DLMO. The remaining 43% have normal circadian timing but behavioral patterns that mimic a circadian disorder. This distinction matters because the treatment approach differs entirely: circadian-based therapies like timed light exposure and melatonin work for the first group but not the second.

Neurodegenerative Disease

Consistently reduced circulating melatonin is found in Alzheimer's disease, Parkinson's disease, and other dementias. Whether this decline drives neurodegeneration or simply reflects it remains unclear, but the association is strong enough that melatonin status may serve as an early signal of brain health changes, particularly when combined with other markers of cognitive function.

Reference Ranges

There are no universally standardized clinical reference ranges for blood melatonin, which places this marker in the emerging category where published values exist but consensus cutpoints are still being refined. The ranges below come from published research and are heavily dependent on the time of day the sample is collected and the age of the person being tested.

These values come from research-grade assays. Many commercial immunoassays lack adequate validation and can produce unrealistically high daytime readings. Mass spectrometry methods are considered the gold standard and can detect levels below 1 pg/mL. If your lab uses an immunoassay, results may not be directly comparable to the ranges above. Always compare your results within the same lab over time for the most meaningful trend.

Tracking Your Trend

A single melatonin measurement tells you relatively little on its own. The within-person variation is about 12 to 15% for 24-hour urine collections of the main melatonin metabolite (6-sulfatoxymelatonin) and as high as 39% for daytime blood measurements. Serum melatonin measured at the same time of day correlates reasonably well year to year (correlation of 0.87 at one year, 0.70 at five years), which means serial measurements do track real biological changes, but you need to be consistent about collection timing.

Get a baseline test, drawn at a consistent time (ideally during your expected peak, which for most people is between midnight and 4 AM, or alternatively as a first-morning urine collection of the metabolite). If you start an intervention like melatonin supplementation, timed light therapy, or a shift in your sleep schedule, retest in 3 to 6 months using the same method and timing. Then monitor at least annually. The trajectory matters far more than any single number, especially with a marker that varies this much day to day.

When Results Can Be Misleading

The most common reason for an unreliable melatonin reading is wrong timing. Melatonin follows a roughly 6-fold swing between day and night in young adults, so a sample drawn a few hours too early or late can miss the peak entirely. Any light exposure above about 200 lux during the collection period (equivalent to a dim indoor room) can suppress your level dose-dependently, with near-complete suppression above 600 lux.

Beta-blockers are the biggest medication confounder. Atenolol and propranolol can suppress nighttime melatonin by 80 to 86% through direct inhibition of the nerve signals that trigger pineal production. This does not mean these drugs are harming your circadian system permanently; it means your test result will look dramatically lower than your true baseline while you are taking them. Carvedilol, interestingly, does not suppress melatonin. NSAIDs like ibuprofen and indomethacin also suppress melatonin production, though the magnitude is less well quantified.

Other factors that can distort a reading: recent surgery (which can delay melatonin onset by 1 to 2 hours and alter the amplitude for at least two nights), BMI above 30 (associated with about 18% lower levels), chronic kidney disease (which blunts rhythmicity), heavy smoking (which is associated with significantly lower levels), and season (levels tend to be higher in winter than summer). High-intensity evening exercise can raise melatonin by nearly 50% acutely and shift the next evening's onset by 1 to 2 hours, so avoid intense workouts in the evening before a test.