Editorial Note
Issue 02 is about sleep — because you asked for it.
When we opened the poll at the end of Issue 01, "sleep optimization during weight loss" was the clear choice. The instinct is right. Sleep is often overlooked in discussions of metabolic health. A small crossover study found that shorter sleep changed what people lost while dieting, and a one-year trial found more weight regain in people who slept less than 6 hours a night. Both findings are limited, and neither shows that a supplement changes these outcomes.1,2
This issue looks at what a few studies show about sleep and weight loss, how some popular sleep supplements have been studied, and where the evidence is limited. We also look at what melatonin and magnesium can and cannot do for sleep. This issue is general information, not medical advice.
— The Kasivit Editorial Team
A small study on sleep and what people lose while dieting
In 2010, a small randomized crossover study at the University of Chicago followed ten overweight adults. Each person followed the same moderate calorie-restricted diet for 14 days on two occasions: once with 8.5 hours and once with 5.5 hours of nighttime sleep opportunity.1 The balance between fat and fat-free mass lost differed between the two conditions.
With 8.5 hours of sleep opportunity, participants lost 1.4 kg of fat; with 5.5 hours they lost 0.6 kg. Shortening sleep decreased the proportion of weight lost as fat by 55% and increased the loss of fat-free body mass by 60% (1.5 kg versus 2.4 kg).1 The authors note that the size and duration of the study were limited.
Participants also reported increased hunger when they slept less.1 A 2008 review describes lower leptin and higher ghrelin levels, which correlate with greater hunger, when sleep is restricted.3 One small study cannot show how these results apply to everyone, but together they suggest that getting enough sleep deserves attention during weight loss.
Nedeltcheva AV et al. Annals of Internal Medicine, 2010. 153(7):435–441.
A look at what small trials and meta-analyses show about magnesium and melatonin for sleep, including their limits and safety considerations.
Read the full article →GLP-1 medications reduce appetite, and eating less can make it harder to meet nutrient needs. A look at six nutrition areas, including magnesium and gut health, to discuss with your prescriber or dietitian.
Read the full article →Sleep and the immune system interact in several ways. A look at what research suggests about sleep loss and immune function.
Read the full article →In this double-blind trial, 46 older adults with primary insomnia received 500 mg of magnesium or placebo daily for 8 weeks. Compared with placebo, the magnesium group had longer sleep time (P = 0.002), better sleep efficiency (P = 0.03), shorter time to fall asleep (P = 0.02) and lower Insomnia Severity Index scores (P = 0.006), with higher blood melatonin (P = 0.007) and lower blood cortisol (P = 0.008). Early-morning awakening differed only marginally (P = 0.08), and the abstract reports no significant difference in total sleep time (P = 0.37). The abstract does not state which form of magnesium was used.4 A pooled analysis of three small trials in 151 older adults found sleep onset about 17 minutes faster than with placebo, but all trials were at moderate-to-high risk of bias and the evidence was rated low to very low quality.5
Researchers limited time in bed to 4 hours per night for 6 nights in 11 young men, then allowed 12 hours per night for 6 nights. After sleep restriction, evening cortisol concentrations were higher (P = 0.0001), glucose tolerance was lower (P < 0.02) and thyrotropin concentrations were lower (P < 0.01) than after recovery sleep.6 The study did not measure fat storage or muscle loss, and its sleep restriction was much more severe than 6 hours, so it cannot show that cortisol explains the body composition findings in the diet study above.
In two 52-week, double-blind, placebo-controlled trials in adults with obesity and moderate-to-severe obstructive sleep apnea, tirzepatide (10 mg or 15 mg, maximum tolerated dose) reduced the apnea-hypopnea index (AHI) by 20.0 events per hour more than placebo in trial 1 and 23.8 events per hour more in trial 2.7 Tirzepatide also reduced body weight. The most common side effects were gastrointestinal and mostly mild to moderate. Trial 1 enrolled people not using positive airway pressure (PAP) therapy and trial 2 enrolled people who were. The trials were funded by the manufacturer and tested tirzepatide, not semaglutide.
The cortisol-sleep-weight triangle: why the loop is self-reinforcing
Researchers have proposed a loop linking sleep, stress hormones and weight, but parts of it are better supported than others. In a small laboratory study, evening cortisol was higher in young men after six nights of restricted sleep.6 A 2008 review describes growth hormone release and cortisol suppression during slow-wave sleep, and links sleep loss with lower leptin, higher ghrelin and greater hunger.3 In the diet study above, shorter sleep shifted weight loss toward fat-free mass and away from fat,1 and in a one-year trial, short sleep was associated with more weight regain.2 We did not find studies in the sources reviewed here showing that lowering cortisol with supplements improves body composition.
Some people report changes in sleep during rapid weight loss, including with GLP-1 medicines. We did not find good-quality evidence on how common this is or why it happens. If sleep problems persist, mention them to your clinician. If you take insulin or other diabetes medicines, ask your prescriber about nighttime blood sugar before changing your diet or adding supplements.
Sleep habits are a common first step: a regular schedule, a dark and cool bedroom, and avoiding caffeine and other stimulants late in the day. Some people also try supplements such as magnesium; the evidence for these is limited, as summarized above. Persistent sleep trouble, or loud snoring with pauses in breathing, is worth discussing with a clinician.
A magnesium glycinate supplement. In one small study of healthy volunteers, about 4% of magnesium oxide was absorbed, while magnesium chloride, lactate and aspartate were better absorbed; we did not find head-to-head studies of glycinate for absorption or for sleep.8 Sleep trials of magnesium have been small and short (see above). The US tolerable upper intake level for supplemental magnesium in adults is 350 mg per day, set in 1997 because larger amounts can cause diarrhea; some researchers argue it should be re-evaluated.9 Check the label for the amount of elemental magnesium per serving and count magnesium from every supplement you take. People with reduced kidney function can accumulate magnesium: in one study of people taking daily magnesium oxide, high blood magnesium was linked to advanced chronic kidney disease and to dose.10 Ask a clinician first if you have kidney disease, take prescription medicines, or are pregnant or breastfeeding. Take as directed on the label.
Shop Magnesium Glycinate →
A multi-ingredient sleep formula. VitaNight combines magnesium with other ingredients; see the product page for the full ingredient list and amounts. It is a supplement, not a treatment for insomnia or any other condition. Ask a clinician or pharmacist before use if you take prescription medicines or other sleep aids or sedatives, are pregnant or breastfeeding, or have a medical condition.
Shop VitaNight →Ashwagandha extract was associated with a small improvement in sleep in a meta-analysis of 5 randomized trials (400 people). Effects were larger in adults diagnosed with insomnia, at doses of 600 mg per day or more, and over 8 weeks or longer. The authors note that data on serious adverse effects are limited and that more safety data are needed before long-term use can be judged.11 Cases of liver injury have been reported, usually appearing after weeks of use and often with jaundice and itching; a 2026 scoping review of 25 patients described one liver transplant and three deaths in people with pre-existing cirrhosis.12,13 Case reports also describe thyrotoxicosis after ashwagandha use.14,15 Ask a clinician before using ashwagandha if you have liver or thyroid disease, take prescription medicines, or are pregnant or breastfeeding. Stop use and seek medical advice if you develop yellow skin or eyes, dark urine or itching. PLOS ONE, 2021.
Short sleep was associated with weight regain after weight loss in a 1-year trial. In a randomized weight-maintenance study, 195 adults with obesity first lost 13.1 kg on a low-calorie diet. Those who slept less than 6 hours a night at the start of the maintenance phase regained 5.3 kg (P = .0008) and had less reduction in body fat percentage, compared with those who slept longer. This is an association; the study did not show that short sleep caused the regain.2 Sleep, 2023.
Growth hormone is released during slow-wave sleep, when cortisol is suppressed, according to a 2008 review. The review also links sleep loss with lower leptin, higher ghrelin and greater hunger, and suggests that sleep curtailment may be a modifiable risk factor for obesity and type 2 diabetes. It summarizes laboratory and population evidence rather than a single trial.3 Sleep Medicine, 2008.
Melatonin has modest effects on sleep. A meta-analysis of 19 randomized trials (1,683 people with primary sleep disorders) found that melatonin shortened the time to fall asleep by about 7 minutes, lengthened total sleep time by about 8 minutes, and modestly improved overall sleep quality.16 The abstract does not report results for slow-wave sleep, REM sleep or cortisol. PLOS ONE, 2013.
References: (1) Nedeltcheva AV, et al. Ann Intern Med. 2010;153:435-41. PubMed · DOI (2) Bogh AF, et al. Sleep. 2023;46:zsac295. PubMed · DOI (3) Van Cauter E, et al. Sleep Med. 2008;9 Suppl 1:S23-8. PubMed · DOI (4) Abbasi B, et al. J Res Med Sci. 2012;17:1161-9. PubMed (5) Mah J, Pitre T. BMC Complement Med Ther. 2021;21:125. PubMed · DOI (6) Spiegel K, et al. Lancet. 1999;354:1435-9. PubMed · DOI (7) Malhotra A, et al. N Engl J Med. 2024;391:1193-1205. PubMed · DOI (8) Firoz M, Graber M. Magnes Res. 2001;14:257-62. PubMed (9) Costello R, et al. Adv Nutr. 2023;14:973-982. PubMed · DOI (10) Mori H, et al. J Clin Biochem Nutr. 2019;65:76-81. PubMed · DOI (11) Cheah KL, et al. PLoS One. 2021;16:e0257843. PubMed · DOI (12) McIntyre D, et al. Cureus. 2026;18:e109764. PubMed · DOI (13) Björnsson HK, et al. Liver Int. 2020;40:825-829. PubMed · DOI (14) Kamal HI, et al. Cureus. 2022;14:e23494. PubMed · DOI (15) Hayashi M, et al. Cureus. 2024;16:e55352. PubMed · DOI (16) Ferracioli-Oda E, et al. PLoS One. 2013;8:e63773. PubMed · DOI (17) Min JS, et al. Drug Des Devel Ther. 2025;19:3509-3537. PubMed · DOI
This issue is general information, not medical advice, and is not intended to diagnose, treat, cure or prevent any condition. Individual responses to supplements vary. Talk to a doctor or pharmacist before using supplements if you take prescription medicines, are pregnant or breastfeeding, have kidney, liver or thyroid disease, or are giving a supplement to a child. GLP-1 medicines can change how some oral medicines are absorbed, so ask your prescriber or pharmacist about timing before adding supplements.17 Do not stop or change any prescribed medicine or treatment, including CPAP, without talking to your prescriber.
Each issue summarizes published research in plain language: what the studies found and where they are limited. No hype, no sponsored content.
- Deep dives into supplement science
- Summaries of published studies, with sources
- Label walk-throughs and cautions
- No ads. No affiliate links. Ever.
Free · Research summaries and occasional Kasivit news by email · Unsubscribe anytime