Enhance Your Learning Speed & Health Using Neuroscience Based Protocols | Dr. Poppy Crum

Heating the sleep environment toward the end of the night increases REM sleep, whereas cooling it at the beginning of the night increases deep sleep.

"I was told that heating your sleep environment toward the end of the night increases your REM sleep dramatically, whereas cooling it at the beginning of the night increases your deep sleep." (said at 1:09:11)

The claim pairs a partially supported concept with an exaggerated assertion. Controlled studies show that facilitating body cooling (e.g., via high heat capacity mattresses or lowering ambient temperature) can moderately increase slow-wave sleep (N3 / deep sleep), reflecting the body's natural circadian core body temperature decline. However, heating the sleep environment does not produce 'dramatic' increases in REM sleep; excessive or elevated nocturnal heat generally fragments sleep architecture and suppresses REM sleep, although mild thermal adjustments that parallel circadian rewarming can assist sleep termination. The magnitude ('dramatically') and specific heating mechanism for boosting REM are overstated.

• partial: Enhanced conductive body heat loss during sleep increases slow-wave sleep and calms the he… (Scientific reports 2024) · cited 26x in the literature

  "The main findings were an increase in nocturnal sleep stage N3 (7.5 ± 21.6 min/7.5 h, mean ± SD; p = 0.0038) and a decrease in heart rate (- 2.36 ± 1.08 bpm, mean ± SD; p < 0.0001); sleep stage REM did not change (p = 0.3564). Subjects with a greater degree of body cooling exhibited a significant increase in nocturnal N3 and a decrease in REM sleep, mainly in the second part of the night." (abstract, results)

  pubmedfull study (doi)
• contradicts: Nocturnal heat impairs sleep architecture and autonomic activity in young men, with BMI-de… (Sleep medicine 2026)

  "Exposure to 30°C reduced total sleep time, sleep efficiency, and overnight cardiac parasympathetic activity in both groups. Sleep architecture showed BMI-dependent effects: individuals with NW exhibited heat-sensitive reductions in average slow-wave sleep (SWS) period duration and increased N1%" (abstract, results)

  pubmedfull study (doi)

Diabetes can be detected from acoustic voice analysis due to spectral sound changes associated with dehydration.

"diabetes, heart disease both show up in voice. Diabetes shows up because uh you can pick up on uh dehydration uh in the in the voice. Uh you much again, I'm I'm a sound person in my heart, in my past, and if you look at the spectrum of sound, you're going to see changes that show up. You know, there are very consistent things in a voice that show up with dehydration in the spectral, you know, salience" (said at 1:58:20)

While emerging research explores machine learning algorithms using acoustic voice features (such as fundamental frequency, pitch variation, jitter, and shimmer) to predict type 2 diabetes, claims that diabetes can be reliably detected from voice through dehydration-related spectral changes are overstated. A 2024 systematic review and meta-analysis of acoustic and aerodynamic measures in type 2 diabetes found no statistically significant difference in fundamental frequency, jitter, shimmer, or noise-to-harmonic ratio between diabetic patients and controls. Pilot studies using smartphone audio have shown modest predictive ability (e.g., 70-75% accuracy when combined with age and BMI) or minor intra-individual pitch shifts with acute glucose changes, but these remain experimental vocal biomarkers rather than established diagnostic tools driven by clear spectral markers of dehydration.

• contradicts: Effect of Diabetes Mellitus Type 2 on Voice: A Systematic Review and Meta-Analysis. (Folia phoniatrica et logopaedica : official organ of the International Association of Logopedics and Phoniatrics (IALP) 2024) · cited 8x in the literature

  "There was also no significant difference in any of the acoustic and aerodynamic measures between patients with type 2 diabetes and controls. These findings can be ascribed to the high resilience of the laryngeal muscles to the adverse effect of systemic diseases. There is no consensus in the literature that the prevalence of voice symptoms in diabetic patients is significantly higher than that reported in healthy subjects." (abstract, results, passage verified)

  pubmedfull study (doi)
• context: Linear effects of glucose levels on voice fundamental frequency in type 2 diabetes and ind… (Scientific reports 2024) · cited 9x in the literature

  "Glucose levels and fundamental frequency (F0) had a significant positive association within an individual, and a 1 mg/dL increase in CGM recorded glucose corresponded to a 0.02 Hz increase in F0 (CI 0.01-0.03 Hz, P < 0.001)." (abstract, results)

  pubmedfull study (doi)
• partial: Acoustic Analysis and Prediction of Type 2 Diabetes Mellitus Using Smartphone-Recorded Voi… (Mayo Clinic proceedings. Digital health 2023) · cited 35x in the literature

  "Significant differences were found between voice recordings of nondiabetic and T2DM men and women, both in the entire dataset and in an age-matched and body mass index (BMI [calculated as the weight in kilograms divided by the height in meters squared])-matched sample... Incorporating these features with age and BMI, the optimal prediction models achieved accuracies of 0.75±0.22 for women and 0.70±0.10 for men through 5-fold cross-validation" (abstract, results, passage verified)

  pubmedfull study (doi)