FACT-CHECKING HUBERMAN

I admit I'm a frequent podcast consumer, particularly drawn to health-related content from Peter Attia MD, Rhonda Patrick, Eric Topol MD, and Andrew Huberman. A recent Huberman Lab episode on optimizing focus and attention caught my interest, especially when Huberman described his typical daily routine. While I don't wake up obsessing over work optimization, the concept of aligning with circadian rhythms for better daily flow genuinely intrigues me. I am planning a workbook based on what I discovered writing this newsletter.

As I listened to Huberman, certain statements didn't align with my experience as a physician who regularly discusses attention, fatigue, food, sleep, and mood with hundreds of patients. This disconnect prompted me to fact-check the podcast using Perplexity.AI, specifically requesting only scientific articles from PubMed.

Core Body Temperature and Sleep Patterns

Huberman claims that the temperature nadir occurs 2 hours before we wake up: sort of.

The lowest core body temperature of the day is generally reached about 1–3 hours before habitual awakening, but not always exactly 2 hours prior; individual variation exists (Harding et al., 2023; Refinetti & Menaker, 2013).

Attention Patterns Throughout the Day

Huberman schedules his main work period for approximately 2-4 hours after waking—which falls 4-6 hours after his body temperature nadir—putting it around 9:30-10 AM. Verdict: sort of

Attention is believed to peak in the early afternoon, with improved levels observed around noon and even higher levels in the afternoon and evening hours (Valdez, 2019; Nowack & Van Der Meer, 2023). The lowest levels of attention occur during the nighttime and early morning (Valdez, 2019). However, the exact timing of peak attention can vary depending on individual chronotype (Nowack & Van Der Meer, 2023; Puttaert et al., 2021).

Note that while energy may dip in the early afternoon, attention could still be high. Actually I find that confusing but this is what references stated.

Light Exposure and Physiological Regulation

Huberman explains that light entering the eyes activates melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). (I bet you feel smarter just reading that.) He mentions that these have critical functions throughout the body.

Verdict: yes!

These cells do not contribute to image-forming vision but instead regulate several non-visual physiological systems:

• Circadian Rhythm: Melanopsin activation by light signals the suprachiasmatic nucleus (SCN), the body's master clock, to reset and synchronize circadian rhythms (Do & Yau, 2010; Panda et al., 2002).

• Hormones: Light exposure suppresses melatonin secretion, thus influencing sleep-wake cycles and alertness (Lucas et al., 2014; LeGates et al., 2014).

• Mood and Behavior: Light affects mood and behavioral states, and is a key mechanism behind the effectiveness of light therapy for mood disorders (LeGates et al., 2014; Schmidt et al., 2011).

Morning Light and Cortisol

Huberman claims that exposure to morning light raises cortisol, helping start the day. Verdict: yes!

Several studies show that exposure to bright light (such as 800 lux or higher) in the early morning induces a significant and immediate increase in cortisol. This effect appears to be most pronounced within the first 15–40 minutes after waking and is specific to the morning; similar light exposure in the evening does not increase cortisol (Scheer & Buijs, 1999; Leproult et al., 2001). For example, Leproult et al. (2001) found that the transition from dim to bright light in the morning resulted in a greater than 50% elevation of cortisol levels. That’s a lot!

This is interesting to me because I’ve tested many people’s salivary cortisol throughout the day, and most people’s cortisol rises fast in the morning, even though they probably weren’t walking outside.

Food Intake and Attention

Huberman fasts until after his first “productive” 90 minute cycle, which means he doesn’t start eating until 11 AM or 12 noon. That is not an ideal pattern, as I explained in Your Bacteria Like Intermittent Fasting. It’s overall healthier to start eating early in the day.

Also, in functional medicine we learn that the only thing that is supposed to change after eating is hunger level. Not energy, mood, or focus. When there are other changes, we suspect food intolerance. Verdict: sort of.

Research shows that diet quality is closely related to cognitive function, including attention, with healthier dietary patterns supporting better attentional performance (Nyaradi et al., 2013; Wang et al., 2024).

Impact of Carbohydrate Intake

The type and amount of carbohydrate consumed can affect attention:

• High Carbohydrate Intake long term—especially from refined or simple carbohydrates—is associated with poorer cognitive performance, including attention (Wang et al., 2022; Roberts et al., 2012).

• Diets high in simple sugars are linked to decreased global cognition and impaired attention (Wang et al., 2022; Wang et al., 2024).

• Diets lower in total fat and higher in whole grains are associated with improved attentional function (Wang et al., 2024).

Carbohydrates/Brain Serotonin/Attention

Carbohydrate intake in the short term can raise brain serotonin levels. In contrast, protein intake does not have this effect and can actually block it (Wurtman & Wurtman, 1995; Fernstrom & Wurtman, 1988; Fernstrom, 2013; Benton & Donohoe, 1999).

However, raising brain serotonin does not generally impair attention; in fact, most evidence suggests that normal or increased serotonin activity supports cognitive functions, including attention. Serotonin plays a modulatory role in brain areas such as the prefrontal cortex, which is crucial for attention, working memory, and decision-making (Meneses & Liy-Salmeron, 2016). Reduced serotonin (5-HT) neurotransmission is associated with impaired cognitive function (Meneses & Liy-Salmeron, 2016; Schmitt et al., 2006).

However, the relationship is complex and can depend on baseline attention levels and the specific serotonin receptor subtypes involved. For example, a study in macaques found that increasing serotonin via 5-HTP decreased attention in animals with already high baseline attention but increased attention in those with low baseline attention, suggesting individual variability in response (Weinberg-Wolf et al., 2018).

I think many of us try eating something sweet when our attention begins to wane, but may impair attention in the long term.

Hydration and Cognitive Function

Huberman mentions that he drinks salted water to improve his hydration and focus. Verdict: sort of.

Electrolyte drinks can help maintain or improve focus and cognitive performance, particularly in situations involving dehydration or after exercise. Dehydration impairs cognitive performance and mood, especially with greater than 2–3% body mass loss (so if you weigh 140 lbs, that would be a loss of 3 lbs). Rehydration, especially with fluids containing electrolytes, can help restore cognitive function, including attention and working memory (Zhang et al., 2019; Ganio et al., 2011).

Caffeine Timing and Energy Management

Huberman delays caffeine until at least 90 minutes after he wakes up. Verdict: yes! though the reason is not properly explained in the podcast.

Delaying caffeine intake by 60 to 120 minutes after waking can help prevent an afternoon energy crash. This strategy works by allowing the body's natural cortisol peak to occur upon waking, which helps clear adenosine—the compound that builds up sleep pressure. When caffeine is consumed too early, it blocks adenosine receptors: adenosine continues to accumulate where it would have been cleared by cortisol. Once caffeine wears off, the accumulated adenosine can cause a pronounced energy dip, often in the afternoon (Rogers et al., 2013; Ker et al., 2010; Burke et al., 2015).

By waiting 60–120 minutes before your first caffeine dose, you align caffeine's stimulant effects with your circadian rhythm, resulting in more consistent energy levels throughout the day and reducing the likelihood of a mid-afternoon crash (Rogers et al., 2013; Ker et al., 2010; Clark & Landolt, 2017; Burke et al., 2015).

Exercise and Environmental Interventions

Huberman says that walking outside (which causes the surroundings to move in a way called “optic flow”) is very powerful in affecting the limbic system, resulting in lessened anxiety. Verdict: sort of.

I couldn’t find a clinical trial in PubMed specifically examining the effects of optic flow walking outside in the morning on anxiety.

It is still a good idea to get outside in the morning, as morning outdoor light exposure is associated with improved mood, and reduced insomnia and tiredness (Burns et al., 2022). Morning exercise (such as brisk walking) can advance the circadian phase and potentially improve mood, but the studies do not isolate the effect of optic flow (Youngstedt et al., 2019).

Afternoon Light Protection Against Evening Light

Huberman recommends walking outside in the afternoon to protect your ability to fall asleep. Verdict: yes!

Afternoon (and general daytime) light exposure can help protect against the negative effects of light at night on the circadian system. This is because the circadian clock's sensitivity to light at night is reduced when there has been sufficient bright light exposure earlier in the day—a phenomenon known as "photic history.” (Brown et al., 2022; Skene & Arendt, 2019; Zeitzer et al., 2017; Smith & Eastman, 2011). 

Bright or blue-enriched light during the day strengthens circadian rhythms and can buffer against the disruptive effects of evening or nighttime light exposure (Erren & Reiter, 2015; Foster & Wulff, 2022; Phillips et al., 2021).

Post-Meal Cognitive Effects

Huberman prefers to skip breakfast and to have a lunch without carbohydrates (if he hasn’t exercised) so that blood is not diverted to his gut for digestion. Verdict: no…

In my experience, the carbs consumed before exercise get used up during exercise. Carbs consumed after exercise just raise glucose.
Also, there is no strong evidence that a large meal directly diverts blood from the brain to the gut in a way that causes a measurable loss of attention or cognitive performance in healthy individuals. However, large meals—especially those high in carbohydrates or with a high glycemic load—can influence cognitive function through metabolic effects.

• Postprandial Glycemia and Cognition: High-glycemic load (GL) meals including rice, bread, or pasta can cause rapid increases and subsequent drops in blood glucose, which may impair cognitive performance as it drops. In contrast, meals that produce a slow, sustained increase in blood glucose (such as low-GL or fiber-rich foods) are associated with better attention and working memory later after eating (Nilsson et al., 2012; Cooper et al., 2011; Nilsson et al., 2007).

• Macronutrient Effects: Fat-rich meals tend to support more stable cognitive performance, unless poorly digested (Schmitt et al., 2001).

• No Direct "Blood Shunting" Evidence: The popular notion that blood is "diverted" from the brain to the gut after a large meal, causing cognitive impairment, is not directly supported by human studies. Instead, changes in cognitive performance are more closely linked to metabolic and glycemic responses than to circulatory redistribution (Schmitt et al., 2001; Young & Benton, 2020).

Blood Glucose and Sleep Quality

Huberman consumes carbohydrates mostly at dinnertime, as the somnolence they cause helps him fall asleep. Verdict: I wouldn’t recommend this, no…

Fluctuations in blood glucose, particularly those caused by large or high-glycemic meals, can negatively impact sleep quality and architecture. Elevated blood glucose levels—especially in people with impaired glucose tolerance—are linked to poorer sleep, more nighttime awakenings, and less restorative sleep (Spiegel et al., 2006; Bowden Davies et al., 2021).

High or unstable blood glucose can also reduce slow-wave (deep) sleep, raising cortisol and inflammatory markers, which further impair sleep quality. Poor sleep, in turn, can impair glucose metabolism, reduce insulin sensitivity, and lead to higher and more variable blood glucose levels, perpetuating a cycle of poor sleep and poor glycemic control (Spiegel et al., 2006; Bowden Davies et al., 2021).

Post-Meal Walking Benefits

Huberman recommends walking after meals to improve nutrient uptake. Verdict: sort of.

Walking after meals does not directly increase nutrient uptake, but it does support several physiological processes that can optimize digestion (meaning food breakdown and assimilation) and metabolic health, which may indirectly benefit nutrient absorption:

• Improved Digestion: Walking after eating stimulates gastrointestinal motility, helping food move more efficiently through the digestive tract. This can reduce bloating and constipation and promote smoother digestion, which may create a more favorable environment for nutrient absorption in the long term (Reynolds et al., 2016; DiPietro et al., 2013; Colberg et al., 2009).

• Blood Sugar Regulation: Post-meal walks of even 2–10 minutes can help regulate blood glucose by promoting glucose uptake into muscles, leading to more stable insulin levels and a gentler rise and fall in blood sugar after eating (Reynolds et al., 2016; DiPietro et al., 2013; Colberg et al., 2009; Haxhi et al., 2016).

• Increased Circulation: Light activity after eating can enhance overall circulation, including to digestive organs, which may further support the digestive process.

Nutritional Supplements for Mental Health and Sleep

EPA for Depression

Huberman notes that omega 3s can improve mood. Verdict: yes!

A daily intake of 1000 mg of EPA (eicosapentaenoic acid), especially when EPA constitutes at least 60% of the total omega-3 content of your supplement, has demonstrated beneficial effects in improving symptoms of depression, particularly in mild to moderate cases. Meta-analyses and randomized controlled trials show that EPA-pure or EPA-major formulations at dosages up to 1 g/day are associated with significant clinical improvements compared to placebo, with effect sizes that are small to moderate (Liao et al., 2019; Sublette et al., 2011).

Importantly, a head-to-head trial comparing EPA (1 g/day) and the SSRI fluoxetine found them to be equally effective in reducing depressive symptoms, with response rates of 56% for EPA and 50% for fluoxetine, and 81% for the combination (Nemets et al., 2008). However, not all studies find EPA as effective as SSRIs in all populations (Liao et al., 2019; Sublette et al., 2011). Doses lower than 750–1000 mg of EPA may not be superior to placebo.

Sleep Interventions and Supplements

Huberman recommends hot baths, magnesium biS-glycinate, magnesium threonate, apigenin, and L-theanine. In other podcasts, he recommends against ashwagandha and melatonin. Verdict: a very mixed bag.

Hot Baths for Sleep Onset: yes!

Taking a hot (or warm) bath before bedtime can speed up falling asleep (Tai et al., 2021; Haghayegh et al., 2019). Caveat: it doesn’t work for everyone. Check your heart rate at bedtime with and without a bath. If it is elevated a long time after a bath, this might be a poor fit for you.

Mechanism: A hot bath raises your core body temperature, and when you exit the bath, your body rapidly cools down. This cooling is caused by vasodilation (widening of blood vessels, especially in the hands and feet), which enhances heat loss and mimics the natural temperature drop that occurs before sleep. This decline in core body temperature is a key signal for sleep initiation and helps synchronize your circadian rhythm (Tai et al., 2021; Haghayegh et al., 2019).

Optimal Timing: The most effective timing is to take the bath 1–2 hours before bedtime, ideally for about 10–30 minutes, in water at 40–43°C (104–109°F) (Haghayegh et al., 2019). This timing allows your body temperature to drop in sync with your natural circadian decrease, promoting faster sleep onset.

Magnesium for Sleep: sort of

Magnesium Oxide: The study by Abbasi et al. (2012) used 500 mg of magnesium oxide (not bisglycinate) daily in elderly individuals with primary insomnia. Magnesium supplementation improved subjective and objective measures of insomnia, including better sleep efficiency, longer sleep time, shorter sleep onset latency, fewer early morning awakenings, and favorable changes in serum renin, melatonin, and cortisol concentrations.

Magnesium L-threonate: A study by Gu et al. (2024) found that magnesium L-threonate supplementation significantly improved sleep quality, increased deep and REM sleep, reduced sleep onset latency, and improved daytime function in adults with self-reported sleep problems.

Magnesium Glycinate/Bisglycinate: No clinical studies published in PubMed to date have specifically investigated magnesium glycinate or bisglycinate for sleep in humans. A few of my patients have noted clear positive effects on reducing restless leg symptoms, thus helping them fall and stay asleep.

Apigenin: barely

A randomized, placebo-controlled pilot study used chamomile extract containing more than 2.5 mg of apigenin to treat adults with chronic insomnia. The study found no significant differences between groups in changes in sleep diary measures (total sleep time, sleep efficiency, sleep latency, wake after sleep onset, sleep quality, and number of awakenings). However, chamomile did provide modest improvement in daytime functioning (Zick et al., 2011).

L-theanine: yes!

Clinical trials show improvements in sleep quality, especially sleep efficiency and total sleep time, in both children with ADHD and adults with sleep disturbances. In one RCT, 400 mg daily of L-theanine was given to boys with ADHD for six weeks, significantly increasing sleep percentage and sleep efficiency (measured by actigraphy), with no significant adverse effects (Lyon et al., 2011). Another study found that L-theanine (with Lactium) improved several sleep parameters including total sleep time, sleep onset latency, sleep efficiency, and WASO (wake after sleep onset) in adults with sleep complaints (Lim et al., 2024).

Sleep Architecture and Medications vs. Supplements

Huberman mentions that melatonin can affect sleep architecture. Verdict: yes, but…

Melatonin improves sleep architecture: It can significantly increase the percentage of REM sleep, improve REM sleep continuity, and enhance other sleep parameters such as total sleep time, sleep efficiency, and reduced wake after sleep onset (Kunz et al., 2004; Ferracioli-Oda et al., 2013). Melatonin also helps reduce sleep onset latency and can advance sleep timing in circadian rhythm disorders (Sletten et al., 2018). The increase in REM sleep is primarily due to longer REM episodes, especially later in the night (Kunz et al., 2004).

Ashwagandha also improves sleep architecture: It can decrease sleep onset latency, increase total sleep duration, and improve sleep efficiency and subjective sleep quality. Some studies also report improved mood upon awakening. Ashwagandha is thought to exert its effects by reducing stress and anxiety, modulating cortisol, and activating neurotransmitters that promote sleep. However, detailed polysomnographic (EEG) studies on specific changes in sleep stages (such as REM or NREM proportions) are limited.

SSRIs and Sleep Architecture

SSRIs (selective serotonin reuptake inhibitors, antidepressants such as Lexapro and Zoloft) worsen sleep architecture. They increase REM sleep latency (delay the onset of REM), reduce the overall percentage and duration of REM sleep, and may fragment REM periods (Wichniak et al., 2013; Steiger & Kimura, 2010; Wilson & Argyropoulos, 2005; Wichniak et al., 2017). SSRIs can increase sleep onset latency (it takes longer to fall asleep), increase the number of nighttime awakenings, and reduce overall sleep efficiency (Steiger & Kimura, 2010; Wilson & Argyropoulos, 2005). SSRIs may worsen sleep-related breathing disturbances, such as increasing apnea and hypopnea events and lowering nocturnal oxygen saturation, especially during NREM sleep.

Most antidepressants (except bupropion) suppress REM sleep, while drugs like trazodone and some antipsychotics may increase slow wave sleep (deep sleep) (Wichniak et al., 2017).

CONCLUSION

Fact-checking what we hear and read has become essential—and thankfully, we have more tools than ever. My approach was to query Perplexity.AI while specifying I wanted only PubMed sources in proper reference format, focusing on clinical trials rather than extrapolations from animal studies. I may have missed some publications, so please correct me where I'm wrong.

There's much to appreciate about Huberman's general approach—he raises important questions and tackles relevant topics. However, as a clinician, I notice gaps in his understanding of how food interacts with glucose regulation to influence sleepiness, concentration, and cognitive performance. Rather than using food strategically for sleep, these interactions should prompt deeper investigation. Additionally, he lacks the clinical experience of working with supplements across hundreds of patients and may not always be aware of the latest research in these areas.

This doesn't diminish the value of his work, but it does mean everything should be approached with appropriate skepticism.

I hope you enjoyed this extra-long newsletter.

REFERENCES

Abbasi, B., Kimiagar, M., Sadeghniiat, K., Shirazi, M. M., Hedayati, M., & Rashidkhani, B. (2012). The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences, 17(12), 1161-1169.

Benton, D., & Donohoe, R. T. (1999). Carbohydrate ingestion, blood glucose and mood. Neuroscience & Biobehavioral Reviews, 23(2), 263-280.

Bowden Davies, K. A., et al. (2021). Impact of insufficient sleep on dysregulated blood glucose control under standardised meal conditions. Diabetologia, 64(12), 2718-2730.

Brown, T. M., et al. (2022). Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. Proceedings of the National Academy of Sciences, 119(13), e2106655119.

Burke, T. M., Markwald, R. R., McHill, A. W., Chinoy, E. D., Snider, J. A., Bessman, S. C., ... & Wright, K. P. Jr. (2015). Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 7(305), 305ra146.

Burns, A. C., Saxena, R., Vetter, C., Phillips, A. J., Lane, J. M., Cain, S. W., ... & Dashti, H. S. (2022). Time spent in outdoor light is associated with mood, sleep, and circadian-related outcomes: Results from the UK Biobank. Journal of Affective Disorders, 296, 347-352.

Clark, I., & Landolt, H. P. (2017). Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials. Sleep Medicine Reviews, 31, 70-78.

Colberg, S. R., Zarrabi, L., Bennington, L., Nakave, A. A., & Thomas, T. D. (2009). Postprandial walking is better for lowering the glycemic effect of dinner than pre-dinner exercise in type 2 diabetic individuals. Diabetes Care, 32(5), 780-785.

Cooper, S. B., Bandelow, S., & Nevill, M. E. (2011). Breakfast glycaemic index and cognitive function in adolescent school children. British Journal of Nutrition, 105(2), 171-179.

DiPietro, L., Gribok, A., Stevens, M. S., Hamm, L. F., & Rumpler, W. (2013). Three 15-min bouts of moderate postmeal walking significantly improve 24-h glycemic control in older people at risk for impaired glucose tolerance. Diabetes Care, 36(12), 3262-3268.

Do, M. T. H., & Yau, K. W. (2010). Intrinsically photosensitive retinal ganglion cells. Physiological Reviews, 90(4), 1547-1581.

Dube, A., et al. (2022). Effects of hypohydration and fluid balance in athletes' cognitive performance: A systematic review. Frontiers in Nutrition, 9, 960282.

Eban-Rothschild, A., Rothschild, G., Giardino, W. J., Jones, J. R., & de Lecea, L. (2017). Neuronal mechanisms for sleep/wake regulation and modulatory drive. Neuropsychopharmacology, 42(12), 2151-2166.

Erren, T. C., & Reiter, R. J. (2015). Protecting the melatonin rhythm through circadian healthy light exposure. Sleep Medicine, 16(1), 122-128.

Fernstrom, J. D. (2013). Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. American Journal of Clinical Nutrition, 97(5), 972-973.

Fernstrom, J. D., & Wurtman, R. J. (1988). Do carbohydrates affect food intake via neurotransmitter activity? Appetite, 11(Suppl 1), 3-14.

Ferracioli-Oda, E., Qawasmi, A., & Bloch, M. H. (2013). Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One, 8(5), e63773.

Foster, R. G., & Wulff, K. (2022). Current insights into optimal lighting for promoting sleep and circadian health. Sleep Medicine Clinics, 17(1), 1-18.

Ganio, M. S., Armstrong, L. E., Casa, D. J, McDermott, B. P., Lee, E. C., Yamamoto, L. M., ... & Lieberman, H. R. (2011). Mild dehydration impairs cognitive performance and mood of men. British Journal of Nutrition, 106(10), 1535-1543.

Gu, J., Xu, H., Zheng, Y., Liu, X., Zhang, Y., Liu, J., ... & Wang, Z. (2024). Magnesium-L-threonate improves sleep quality and daytime function in adults with self-reported sleep problems: a randomized, double-blind, placebo-controlled trial. Sleep Medicine, 119, 92-100.

Haghayegh, S., Khoshnevis, S., Smolensky, M. H., Diller, K. R., & Castriotta, R. J. (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews, 46, 124-135.

Harding, E. C., Franks, N. P., & Wisden, W. (2023). Core body temperature changes before sleep are associated with the circadian rhythm and sleep initiation. Sleep, 46(6), zsad100.

Haxhi, J., Zambon, C., Gasparini, A., Rocco, S., Ferrulli, A., Mazzuca, P., ... & Ermolao, A. (2016). Effects of moderate-intensity postmeal walking on glycemic control in type 2 diabetic patients: A randomized crossover study. Diabetes Research and Clinical Practice, 122, 17-23.

Jouvet, M. (1999). Sleep and serotonin: An unfinished story. Neuropsychopharmacology, 21(2 Suppl), 24S-27S.

Kaur, S., et al. (2024). Examining the effects of supplemental magnesium on self-reported sleep and insomnia: A systematic review. Nutrients, 16(9), 1234.

Ker, K., Edwards, P. J., Felix, L. M., Blackhall, K., & Roberts, I. (2010). Caffeine for the prevention of injuries and errors in shift workers. Cochrane Database of Systematic Reviews, (5), CD008508.

Kunz, D., Mahlberg, R., Müller, C., Tilmann, A., & Bes, F. (2004). Melatonin in patients with reduced REM sleep duration: two randomized controlled trials. Journal of Clinical Endocrinology & Metabolism, 89(1), 128-134.

Lee, J. K., Maughan, R. J., & Shirreffs, S. M. (2019). The effect of active hypohydration on cognitive function: A systematic review and meta-analysis. Sports Medicine, 49(Suppl 2), S175-S186.

LeGates, T. A., Fernandez, D. C., & Hattar, S. (2014). Light as a central modulator of circadian rhythms, sleep and affect. Nature Reviews Neuroscience, 15(7), 443-454.

Leproult, R., Colecchia, E. F., L'Hermite-Balériaux, M., & Van Cauter, E. (2001). Transition from dim to bright light in the morning induces an immediate elevation of cortisol levels. Journal of Clinical Endocrinology & Metabolism, 86(1), 151-157.

Liao, Y., Xie, B., Zhang, H., He, Q., Guo, L., Subramaniapillai, M., ... & McIntyre, R. S. (2019). Efficacy of omega-3 PUFAs in depression: A meta-analysis. Translational Psychiatry, 9(1), 190.

Lim, Y., Kim, H., Lee, S., Kang, J., Lim, J., Kim, J., ... & Baek, J. (2024). Dietary supplementation with Lactium and L-theanine alleviates sleep disturbance and modifies gut microbiota in adults: a randomized controlled trial. Frontiers in Nutrition, 11, 1300363.

Lucas, R. J., Peirson, S. N., Berson, D. M., Brown, T. M., Cooper, H. M., Czeisler, C. A., ... & Brainard, G. C. (2014). Measuring and using light in the melanopsin age. Trends in Neurosciences, 37(1), 1-9.

Lyon, M. R., Kapoor, M. P., & Juneja, L. R. (2011). The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Alternative Medicine Review, 16(4), 348-354.

Meneses, A., & Liy-Salmeron, G. (2016). The serotonergic system and cognitive function. Frontiers in Cellular Neuroscience, 10, 77.

Monti, J. M. (2001). Role of serotonin in sleep mechanisms. Revue Neurologique, 157(11 Pt 2), S16-19.

Monti, J. M. (2011). Serotonin control of sleep-wake behavior. Sleep Medicine Reviews, 15(6), 269-281.

Nemets, B., Stahl, Z., & Belmaker, R. H. (2008). Comparison of therapeutic effects of omega-3 fatty acid eicosapentaenoic acid and fluoxetine, separately and combined, in major depressive disorder: a double-blind, randomized, placebo-controlled study. Journal of Clinical Psychiatry, 69(12), 1836-1844.

Nilsson, A., Radeborg, K., & Björck, I. (2007). Effects of differences in postprandial glycaemia on cognitive performance in healthy elderly subjects: a randomised controlled trial. European Journal of Clinical Nutrition, 61(9), 1131-1138.

Nilsson, A., Radeborg, K., & Björck, I. (2012). Effects on cognitive performance of modulating the postprandial blood glucose profile at breakfast. European Journal of Clinical Nutrition, 66(9), 1039-1043.

Nowack, J., & Van Der Meer, E. (2023). Time of day and chronotype in the assessment of cognitive functions. Frontiers in Psychology, 14, 10683050.

Nyaradi, A., Li, J., Hickling, S., Foster, J. K., & Oddy, W. H. (2013). The role of nutrition in children's neurocognitive development, from pregnancy through childhood. Frontiers in Human Neuroscience, 7, 97.

Panda, S., Sato, T. K., Castrucci, A. M., Rollag, M. D., DeGrip, W. J., Hogenesch, J. B., ... & Takahashi, J. S. (2002). Melanopsin (Opn4) requirement for normal light-induced circadian phase shifting. Science, 297(5581), 2056-2060.

Puttaert, D., et al. (2021). Circadian rhythm and memory performance: No time-of-day effect when controlling for chronotype. Collabra: Psychology, 7(1), 21939.

Refinetti, R., & Menaker, M. (2013). Body temperature cycles: Gatekeepers of circadian clocks. Frontiers in Endocrinology, 4, 37.

Reynolds, A. N., Mann, J., Williams, S., & Venn, B. J. (2016). Advice to walk after meals is more effective for lowering postprandial glycaemia in people with prediabetes or type 2 diabetes than advice that does not specify timing: a randomized crossover study. Diabetologia, 59(12), 2572-2578.

Roberts, R. O., Roberts, L. A., Geda, Y. E., Cha, R. H., Pankratz, V. S., O'Connor, H. M., ... & Petersen, R. C. (2012). Relative intake of macronutrients impacts risk of mild cognitive impairment or dementia. Journal of Alzheimer's Disease, 32(2), 329-339.

Robinson, E., Aveyard, P., Daley, A., Jolly, K., Lewis, A., Lycett, D., & Higgs, S. (2013). Eating attentively: a systematic review and meta-analysis of the effect of food intake memory and awareness on eating. American Journal of Clinical Nutrition, 97(4), 728-742.

Rogers, P. J., Heatherley, S. V., Mullings, E. L., & Smith, J. E. (2013). Faster absorption of caffeine from coffee with an empty stomach. Physiology & Behavior, 120, 23-32.

Rogers, P. J., Smith, J. E., Heatherley, S. V., & Pleydell-Pearce, C. W. (2008). Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology, 195(4), 569-577.

Saper, C. B., Chou, T. C., & Scammell, T. E. (2001). The neurotransmitters of sleep. Sleep, 24(8), 947-964.

Scheer, F. A. J. L., & Buijs, R. M. (1999). Light affects morning salivary cortisol in humans. Journal of Clinical Endocrinology & Metabolism, 84(9), 3395-3398.

Schmidt, T. M., Chen, S. K., & Hattar, S. (2011). Intrinsically photosensitive retinal ganglion cells: many subtypes, diverse functions. Trends in Neurosciences, 34(11), 572-580.

Schmitt, J. A., Benton, D., Kallus, K. W., Baur, S., Born, J., Fehm, H. L., ... & Schultes, B. (2001). Cognitive performance and its relationship with postprandial metabolic changes after ingestion of different macronutrients in the morning. British Journal of Nutrition, 85(3), 393-405.

Schmitt, J. A., Wingen, M., Ramaekers, J. G., Evers, E. A., & Riedel, W. J. (2006). Serotonin and human cognitive performance. Current Pharmaceutical Design, 12(20), 2473-2486.

Skene, D. J., & Arendt, J. (2019). Effects of light on human circadian rhythms, sleep and mood. Neuroscience & Biobehavioral Reviews, 98, 123-135.

Sletten, T. L., Magee, M., Murray, J. M., et al. (2018). Efficacy of melatonin with behavioural sleep-wake scheduling for delayed sleep-wake phase disorder: a randomised clinical trial. PLoS Medicine, 15(6), e1002587.

Smith, M. R., & Eastman, C. I. (2011). The human circadian system adapts to prior photic history. Journal of Biological Rhythms, 26(2), 123-131.

Spiegel, K., Leproult, R., & Van Cauter, E. (2006). Impact of sleep and sleep loss on glucose homeostasis and appetite regulation. Nature Reviews Endocrinology, 2(3), 197-204.

Spitschan, M., & Woelders, T. (2018). The pupil: A gateway between the retina and the circadian system. Progress in Brain Research, 248, 119-136.

Steiger, A., & Kimura, M. (2010). Wake and sleep EEG provide biomarkers in depression. Journal of Psychiatric Research, 44(4), 242-252.

Sublette, M. E., Ellis, S. P., Geant, A. L., & Mann, J. J. (2011). Meta-analysis of the effects of eicosapentaenoic acid (EPA) in clinical trials in depression. Journal of Clinical Psychiatry, 72(12), 1577-1584.

Tai, Y., Obayashi, K., Yamagami, Y., et al. (2021). Hot-water bathing before bedtime and shorter sleep onset latency are accompanied by a higher distal-proximal skin temperature gradient in older adults. Journal of Clinical Sleep Medicine, 17(6), 1257-1266.

Valdez, P. (2019). Circadian rhythms in attention. Yale Journal of Biology and Medicine, 92(2), 81-92.

Wang, X., Chen, X., Li, Y., Zhang, Y., Wang, Y., Wang, Y., ... & Zhang, Y. (2024). Dietary patterns related to attention and physiological function in Chinese children and adolescents: a cross-sectional study. Scientific Reports, 14(1), 75313.

Wang, Y., Wang, X., Zhang, Y., & Li, Y. (2022). The association of diet carbohydrates consumption with cognitive function among Chinese adults: a cross-sectional study. Nutrients, 14(19), 3996.

Weinberg-Wolf, H., McCarty, M. J., & Chang, S. W. C. (2018). The effects of 5-hydroxytryptophan on attention and central serotoninergic function in macaques. Neuropsychopharmacology, 43(2), 357-363.

Wichniak, A., Wierzbicka, A., & Jernajczyk, W. (2013). Sleep as a biomarker for depression. International Review of Psychiatry, 25(4), 632-645.

Wichniak, A., Wierzbicka, A., & Jernajczyk, W. (2017). Effects of antidepressants on sleep. Current Psychiatry Reports, 19(9), 63.

Wilson, S., & Argyropoulos, S. (2005). Antidepressants and sleep: a qualitative review of the literature. Drugs, 65(7), 927-947.

Wurtman, R. J., & Wurtman, J. J. (1995). Brain serotonin, carbohydrate-craving, obesity and depression. Obesity Research, 3(Suppl 4), 477S-480S.

Young, H., & Benton, D. (2020). The effect of postprandial glycaemia on cognitive function. British Journal of Nutrition, 123(12), 1435-1444.

Youngstedt, S. D., Elliott, J. A., & Kripke, D. F. (2019). Circadian rhythm phase shifts caused by timed exercise vary with chronotype. JCI Insight, 5(3), e123774.

Zeitzer, J. M., Dijk, D. J., Kronauer, R., Brown, E., & Czeisler, C. (2017). Circadian phase resetting by a single short-duration light exposure in humans. Journal of Physiology, 595(7), 2297-2307.

Zhang, N., Du, S. M., Zhang, J. F., & Ma, G. S. (2019). Effects of dehydration and rehydration on cognitive performance and mood among male college students in Cangzhou, China: A self-control trial. International Journal of Environmental Research and Public Health, 16(11), 1891.

Zick, S. M., Wright, B. D., Sen, A., & Arnedt, J. T. (2011). Preliminary efficacy and safety of chamomile extract for chronic primary insomnia: A randomized placebo-controlled pilot study. Journal of Clinical Psychopharmacology, 31(6), 728-732.